May 21, 1996 - of a pesticide-susceptible laboratory strain of the tufted apple bud moth, Platynota idaeusa/ .... centrations were chosen to generate between 20.
HORTICULTURAL
ENTOMOLOGY
Stage Specificity of Various Insecticides to Tufted Apple Bud Moth Larvae (Lepidoptera: Tortricidae) D. J. BIDDINGER\
L. A. HULL2, ANDE. G. RAJOTIE3
J. Econ. Entomol. 91(1): 200-208 (1998) ABSTRACT The stage specificity of azinphosmethyl, abamectin, fenoxycarb, hexaHumuron, and tebufenozide wasdetermined through diet incorporation on the neonate, 3rd, and 5th instars of a pesticide-susceptible laboratory strain of the tufted apple bud moth, Platynota idaeusa/is (Walker). Mortality was determined 7 and 14 d after initial exposure and at adult eelosion. Ovicidal activity with these same compounds and diflubenzuron was determined with topical applications to freshly laid eggs «24 h). Although the mortality of the different larval stages did not increase significantlyafter 7 d with azinphosmethyl, the LC50sof the 3rd and 5th instars were 90 and 110 times higher than those of the neonates. Mortality with all other compounds tested increased after the initial 7-d reading. Abamectinwas very stage specificto neonate larvae during the initial mortality readings (130-170 times), but delayed mortality in the later instars increased with time, so that by adult eclosion stage, specificity was reduced to 3- 8 times. Stage specificity of hexaflumuron and tebufenozide was relatively low across larval instars, but fenoxycarbwas ineffective on neonates and 200 times more effective on 5th than on 3rd instars. Azinphosmethyl, hexaflumuron, and fenoxycarb were the most ovicidal compounds tested. KEY WORDS Platynota idaeusa/is, stage specificity, insect growth regulators, abamectin, tebufenozide, fenoxycarb
TUFTEDAPPLEBUDmoth, Platynota idaeusalis (Walker), is the most important direct pest of apples in Pennsylvania primarily because of high levels of resistance to organophosphate insecticides (Knight and Hull 1989a, b). Most organophosphate insecticides are no longer effective for controlling tufted apple bud moth unless they are optimally timed for the most susceptible stages or used in a mixture with the carbamate, methomyl (Biddinger et al. 1993). Several studies have established that organophosphates and carbamates are most effective on the neonates of tufted apple bud moth and that the larvae become more tolerant to these compounds as they develop to later instars (Travis et a1.1981, Rock and Shaltout 1983, Wells et al. 1983). Travis et al. (1981) found the adults to be almost as susceptible to these insecticides as the neonates, but that the pupae were only slightly more susceptible than the last instars. Pyrethroid and carbamate insecticides have been investigated as alternatives to organophosphate insecticides, but they were found to be disruptive to biological control of the European red mite, Panonychus ulmi (Koch), by the coccinellid predator Stethorus punctum punctum (LeConte) and the predaceous mites Amblyseius fallacis Garman and I Rohm & Haas Company, Agricultural Chemicals, 100 Independence Mall West, Philadelphia, PA 19106-2399. • Penn State Fruit Research and Extension Center, P.O. Box 309, Biglerville, PA 17307-0309. J Penn State University, Department of Entomology, 501 ASI Building, State College, PA 16801.
0022-0493/98/0200-0208$02.00/0
Zetzellia mali (Ewing) (David and Horsburgh 1985, Hull and Beers 1985, Hull and Knight 1989). Conserving insecticides compatible with integrated pest management is necessary until alternative compounds such as insect growth regulators or tactics, such as pheromone disruption, are commercially available. Abamectin and various classes of insect growth regulators are being investigated as replacements for organophosphate insecticides in tufted apple bud moth control, but almost nothing is known about their stage specificity toward this pest. Insect growth regulators are selective compounds that interfere with the normal physiology of insects by disrupting growth processes, reproduction, or other critical systems. These types of compounds often are very stage specific because they are dependent on a specific physiological event, such as a molt, in the case of chitin inhibitors or, for juvenile hormone analogs, a stage in larval development when the titers of specific hormones are critical for further development. Ecdysone agonists, such as tebufenozide, also are stage specific in that they have relatively little ovicidal activity and are not toxic to the adults (Biddinger 1993). In most current IGR-type compounds, mortality is often much slower than with conventional neurotoxic compounds, and short-term sublethal effects on the target insect's physiology may become acute over time and cause substantial sublethal effects on reproduction in the succeeding generation (Biddinger 1993). Abamectin is known to cause atypical morphological development and interfere with growth and
© 1998 Entomological Society of America
February 1998
BIDDINGER ET AL.: STAGE SPECIFICITY OF INSECTICIDES TO
reproduction in a manner similar to that observed in some types of insect growth regulators associated with the inhibition of neurosecretory organs that control the release of juvenile hormones (Robertson et al. 1985, Bull 1986, Deecher et al 1990). Abamectin is primarily an agonist of the neurosecretory transmitter, GABA (Lasota and Dybas 1991), and may not be as stage specific as the insect growth regulator insecticides. To determine the stage specificity of these various compounds, laboratory bioassays of an insecticide susceptible strain of were conducted. A diet incorporation method was used to measure their toxicity to various larval instars through multiple mortality readings over time. Ovicidal activity was investigated by dipping egg masses into aqueous solutions. This information will be useful in designing management programs for controlling P. idaeusalis with insect growth regulators and abamectin as they become commercially available. Materials and Methods Bioassays were conducted using an insecticidesusceptible laboratory strain that was maintained at the Penn State Fruit Research and Extension Center, Biglerville, PA. All larvae tested in the laboratory were reared on a semisynthetic lima bean diet in plastic cups at 20 :t 2°C and a photoperiod of 16:8 (L:D) h (Meagher 1985). This strain has been in continuous culture for >10 yr without pesticide selection. It was originally collected from apple orchards in North Carolina (Rock and Shaltout 1983) and was supplemented before 1985 with larvae from Pennsylvania (Meagher 1985). For the diet incorporation bioassays, 7-10 ml of warm lima bean diet was poured into 28-ml plastic cups and allowed to cool for"'" 2 h at room temperature. The diet was then either used immediately or stored in closed plastic bags and refrigerated for up to 2 wk until needed. Aqueous solutions of insecticides were serially diluted, and a range of 6 -10 concentrations plus a distilled water control were applied to the surface of the diet. Insecticide concentrations were chosen to generate between 20 and 80% mortality by adult eclosion. Formulated compounds were placed in aqueous solutions and 0.5 ml was pipetted with a Labsystems Finnpipette repeating dispenser (Labsystems Oy, Helsinki, Finland) onto the surface of the diet and allowed to air-dry for 2-3 h. Fifty larvae were tested per concentration with neonates placed 5 larvae per cup in 10 replicates. Third and fifth instars were placed 2 larvae per cup in 5 replicates of 10 larvae grouped into 5 cups. A minimum of 300 larvae were treated per compound with a minimum of 100 controllarvae. During the drying process, the cups were rotated every 15 min to distribute excess solution evenly on the surface. Test applications with 0.5 ml of an aqueous dye solution penetrated 3-4 mm into the diet. The following insecticides were usedazinphosmethyl (Guthion 35WP [wettable pow-
P. idaeusalis
201
der). Miles, Kansas City, MO); hexaflumuron (Dowco 473 5%EC [emulsifiable concentrate). DowElanco, Indianapolis, IN); abamectin Bla (Agri-Mek 0.15EC, Merck, Rahway, NJ); tebufenozide (RH-5992 2F [flowable). Rohm & Haas, Philadelphia, PA); fenoxycarb (Insegar 25WP, Ciba, Basel, Switzerland). Larvae were placed onto the surface of the treated diet with a camel's-hair brush and the cups were capped until the 1st mortality evaluation 7 d later. Larvae were exposed to the treated diet for 14 d. After 14 d, surviving larvae were transferred to cups containing fresh, untreated diet. At this time, most larvae had developed to the 3rd or 4th instar, and, because of their larger size and to reduce cannibalism, only 2 larvae were placed per cup. Bioassays using the larger 3rd and 5th instars followed the same procedure, but only 2 larvae per cup were used. At the 14-d transfer to the untreated diet, most larvae that were initially exposed as 3rd instars had developed to 5th instar, and those larvae initially exposed as 5th instars had pupated. Because physiologically selective compounds such as insect growth regulators may be relatively slow to cause mortality, 3 mortality readings were taken for all treated larvae at 7 and 14 d and at adult eclosion. Larvae or pupae that did not move when lightly probed and grossly deformed adults were considered dead during these evaluations. The ovicidal activity of these same insecticides was assessed on freshly deposited «24 h) egg masses of this same susceptible strain of tufted apple bud moth. The eggs were deposited on wax paper by adults in I-liter cardboard containers. Egg masses were removed daily and surface sterilized for fungal pathogens in a 5% Clorox solution for 10 s, rinsed in distilled water, and allowed to air dry. An effort was made to test approximately the same number of eggs for each treatment by grouping the egg masses according to size. Five egg masses were used per insecticide concentration, and eggs for each replicate came from the same adult mating chamber and were treated on the same day. Three concentrations were tested: the maximum label rate (I X) or recommended field rate for experimental compounds, half of this rate (1/2X), and 1110 of this rate (II lOX). Egg masses were dipped into aqueous solutions of the various compounds for 5 s and allowed to air-dry for 1-2 h. When dry, the individual egg masses were placed into tightly fitting plastic petri dishes (25 mm diameter). The dishes were placed into plastic bags containing a moist paper towel to maintain high humidity and stored at 20 :t 2°C and a photoperiod of 16:8 (L:D) h for 2 wk until egg hatch was completed. Hatching larvae were removed daily to prevent cannibalism of hatched or unhatched eggs. Mortality was assessed by staining the egg masses with a supersaturated solution of methyl red dye in acetone and counting the total number of eggs, both hatched and unhatched. Each egg mass was counted twice, and if the 2 counts differed by > 10%, a 3rd count was made. The counts
202
Yol. 91, no. 1
JOURNAL OF ECONOMIC ENTOMOLOGY
Table 1. bud moth
Effect of varioUll compoWld8 through diet incorporation
Chemical
Azinphosmethyl 35 WP Azinphosmethyl 35 WP Azinphosmethyl 35 WP Hexaflumuron 5% EC Hexaflumuron 5% EC Hexaflumuron 5% EC Tebufenozide 2 F Tebufenozide 2 F Tebufenozide 2 F Abamectin 0.15 EC Abamectin 0.15 EC Abamectin 0.15 EC Fenoxycarb 25 WP Fenoxycarb 25 WP Fenoxycarb 25 WP
on 8Ullceptible laboratory-atrain
neonate larvae of the tufted apple
Neonate larvae
Time of mortality reading:
n
7 14 AE 7 14 AE 7 14 AE 7 14 AE 7 14 AE
300 200 250 450 300 350 350 250 300 250 250 200 300 300 300
b
Slope ± SE
c"
1.99 ± 2.08 ± 1.47 ± 0.81 ± 2.68 ± 2.39 ± 2.80 ± 4.00 ± 1.34 ± 1.60 ± 1.74 ± 14.57 ±
9.3 22.4 28.6 9.0 20.3 25.8 9.3 22.4 28.6 9.3 22.4 28.6 9.3 20.3 25.8
0.25 0.30 0.28 0.09 0.58 0.56 0.34 0.48 0.24 0.18 0.27 3.26
ppm
LC"" 95% CL 2.62-5.20 3.49-7.40 1.29-4.28 5.80-24.2 1.38-2.65 0.42-1.00 1.30-1.98 0.93-1.36 0.06-0.32 0.18-0.41 0.05-0.13 0.05-0.07
3.96 5.37 2.77 12.0 1.98 0.74 1.63 1.12 0.18 0.28 0.08 0.06
LCgo ppm
95% CL
17.4 22.2 20.6 460 5.95 2.54 4.67 2.35 1.65 1.76 0.45 0.08
12.7-27.8 15.1-42.1 13.0-48.6 158-3,230 4.09-13.0 1.76-6.24 3.61-6.84 1.88-3.30 0.96-4.83 1.07-3.60 0.26-1.29 0.07-0.09
-. Fiducial limits not reported because g > 0.50 (LeOra Software 1987). "Mortality observations made at 7 and 14 d after initial exposure and at adult eelosion (AE). b Number of larvae tested. C Control mortality.
were averaged to give the total number of hatched and unhatched eggs. Results from bioassays of each concentration on each instar were pooled and analyzed with the pro-' bit option of POLO (LeOra Software 1987). Instar toxicity ratios were computed as simple proportions comparing the LCsos of each compound at each larval instar with the LCsos of the other instars. Confidence limits at the 95% level were calculated for these ratios by using the variance- covariance matrix of both concentration-mortality lines being compared (Robertson and Preisler 1992). Egg mortality was analyzed using analysis of variance (ANaYA), and treatment means were transformed Table 2. motIt
using log (y + 1) and separated by the Fisher least squared denominator (LSD) multiple range test (Abacus Concepts 1989). Results Mortality of neonate and 3rd- and 5th-instar tufted apple bud moth exposed to azinphosmethyl did not increase significantly at the LCso level after the 7-d mortality readings (Tables 1-3). In contrast, the insect growth regulators hexaflumuron and tebufenozide continued to cause additional mortality after the 7-d readings. Mortality was particularly delayed in larvae treated with the chitin inhibitor
Effect of variou8 compoWld8 through diet incorporation on 8u8ceptible laboratory-atrain
Chemical
Azinphosmethyl 35 WP Azinphosmethyl 35 WP Azinphosmethyl 35 WP Hexaflumuron 5% EC Hexaflumuron 5% EC Hexaflumuron 5% EC Tebufenozide 2 F Tebufenozide 2 F Tebufenozide 2 F Abamectin 0.15 EC Abamectin 0.15 EC Abamectin 0.15 EC Fenoxycarb 25 WP Fenoxycarb 25 WP Fenoxycarb 25 WP
3rt! i""lar8 of the tufted apple bud
3rd instar
Time of mortality reading:
nb
if
Slope ± SE
7 14 AE 7 14 AE 7 14 AE 7 14 AE 7 14 AE
250 250 250 320 320 230 250 250 250 250 350 300 530 530 530
5.0 15.0 20.0 2.0 5.6 25.0 8.6 11.4 35.0 2.5 3.0 13.8 0.0 5.8 10.0
2.15 ± 0.38 5.79 ± 1.53 6.40 ± 1.40 1.48 ± 4.51 ± 2.49 ± 4.26 ± 4.29 ± 1.50 ± 1.52 ± 1.33 ±
ppm 344 391 389
LCoo
LC"" 95% CL
ppm
95% CL
256-457 313-445 316-449
1,360 652 617
879-3,390 551-1,020 522-910
0.23 1.10 0.36 0.94 0.69 0.46 0.17 0.16
0.80 0.86 7.93 4.37 3.03 48.0 1.67 0.18
0.25-1.39 0.58-1.05 6.25-9.89 3.02-5.32 2.36-3.67 30.0-207 1.11-2.29 0.09-0.30
0.78 ± 0.14
47.07
24.7-109
-, Fiducial limits not reported because g > 0.50 (LeOra Software 1987). "Mortality observations made at 7 and 14 d after initial exposure and at adult eelosion (AE). b Number of larvae tested. C Control mortality.
5.83 1.65 25.9 8.74 6.03 344 11.7 1.64
2,120
3.76-11.4 1.36-2.42 19.1-42.4 7.26-12.09 4.93-8.09 113-26,400 7.93-20.7 0.97-3.59
559-36,600
February 1998 Table 3. moth
BIDDINGER
ET AL.: STAGE
SPECIFICITY
OF INSECTICIDES
TO
P. idaeusalis
Effect of variou. compOtmdo through diet incorporation on susceptible laboratory-strain
Chemical
Time of mortality reading,R
Azinphosmethyl 35 WP Azinphosmethyl 35 WP Azinphosmethyl 35 WP Hexallumuron 5% EC Hexallumuron 5% EC Hexallumuron 5% EC Tebufenozide 2 F Tebufenozide 2 F Tebufenozide 2 F Abamectin 0.15 EC Abamectin 0.15 EC Abamectin 0.15 EC Fenoxycarb 25 WP Feuoxycarb 25 WP Fenoxyearb 25 WP
7 14 AE 7 14 AE 7 14 AE 7 14 AE 7 14 AE
203
5th inotars of the tufted OI'J1lebud
5th instars" nil
210 210 320 300 260 280 250 250 340 250 250 220 250 250 250
C
C
0.0 2.6 12.4 0.0 2.5 13.3 0.0 2.6 12.4 0.0 2.6 12.9 0.0 2.8 20.0
Slope:!: SE 2.77:!: 0.75 2.80:!: 0.73 2.70:!: 0.42
LCao
LCso ppm 436 355 338
95% CL
ppm
354-778 297-548 278-401
1,270 1,020 1,010
1.03:!: 0.17 1.99 :!: 0.23 2.44:!: 0.40 2.76:!: 0.41 4.14:!: 0.86 0.96:!: 0.26 1.39:!: 0.23 1.65:!: 0.34
3.18 0.85 7.04 3.02 2.52 35.4 3.94 0.45
1.19-5.46 0.35-1.63 5.59-9.54 1.92-3.89 1.07-3.22 15.9-1,080 2.74-5.27 0.12-0.85
1.04 :!: 0.26
0.23
0.04-0.48
95% CL 732-7,430 620-5,700 763-1,670
55.3 3.73 23.60 8.82 5.14 771 33.1 2.70
3.92
30.5-173 1.90-16.0 14.8-76.] 6.78-14.5 4.01-12.8 110-7,548,000 19.7-86.4 1.55-6.56
2.22-12.9
-, Fiducial limits not reported because g > 0.50 (LeOra Software 1987). Mortality observations made at 7 and 14 d after initial exposure and at adult eelosion (AE). /, Number of larvae tested. e Control mortality.
a
hexaflumuron. Mortality to this compound was relatively low at the 7-d readings for 3rd and 5th instars, and dose-mortality curves could not be generated for comparison with subsequent mortality readings. Abamectin also continued to cause additional mortality between 7 d and 14 d, but mortality did not increase after the larvae were removed from the treated diet. Fenoxycarb did not cause significant mortality to neonates exposed for 14 d nor was mortality of 3rd and 5th instars quantifiable until adult eclosion. Azinphosmethyl, hexaflumuron, and fenoxycarb were the most ovicidal compounds tested (Table 4). These compounds were equally ovicidal at the 1 X rate, but hexaflumuron and fenoxycarb were more toxic than azinphosmethyl at both the 1/2X and 11l0X rates. Di£lubenzuron and abamectin were relatively ineffective as ovicides at all rates. All compounds, except tebufenozide, followed a negative rate response. Tebufenozide was fairly effective as an ovicide at the highest concentration and followed a negative rate response at the highest 2 concentrations, but mortality at the 1/10X rate was unexpectedly high. It is possible that an unfertilized egg mass was included in the test of this concentration. Although each egg was treated as a replicate, only 5 egg masses were tested for each compound, and the inclusion of an unfertilized egg mass could significantly influence the results. Azinphosmethyl was 90-110 times more toxic to neonate tufted apple bud moth at the 7-d reading than to 3rd and 5th instars, respectively (Table 5). Azinphosmethyl was equally toxic to 3rd and 5th instars. The LCsos of both the 3rd and 5th instars of this insecticide-susceptible laboratory strain were well above the maximum field rate of 300 ppm. Hexaflumuron was 2.5 times more toxic to 3rd instars than to neonates by the l4-d reading, but 4 times less
effective on 5th instars than on 3rd instar. Previously sublethal effects, however, became delayed mortality by adult eclosion so that hexaflumuron was equally effective on all instars. Tebufenozide was most effective on neonate larvae, with 3rd instars being 4-18 times less susceptible depending on the date of evaluation. Fifth instars were generally equally susceptible to tebufenozide as 3rd instars. Neonates were most susceptible to abamectin. Mortality in 3rd and 5th instars exposed to abamectin was delayed so that at the 7- and 14-d readings, this
TobIe 4. Response of freshly laid «24 h) eggs of on iusecticide-susceptible laboratory stroin of the tufted opple bud moth to selected insecticides through immersion in aqueous solulions
Chemical Azinphosmethyl 35 WP
Dillubenzuron
25 WP
Hexallumuron 5% EC
Tebufenozide
2F
Abamectim 0.15 EC
Fenoxycarb 25 WP
Control
Con en, ppm 300 150 30 150 75 15 150 75 15 90 45 9 7.5 3.75 0.75 40 20 4
nil
455 300 298 368 289 304 593 409 299 459 253 402 484 258 408 509 449 367 1,053
Aug. no. eg!!;s/eAAs mass
% e!!;g mortality
91.0 60.0 59.6 73.6 57.8 60.8 118.6 81.8 59.8 91.8 50.6 80.4 96.8 51.6 81.6 101.8 89.8 73.4 58.4
95g" 72e 45e 44c 4]bc 35b 94g 92fg 52d 77e 45e 88f 54d 52d 54d 90fg 86f 78e 27a
" Total number of eggs tested per concentration. /, Means followed by the same letter are not statistically different at alpha = 0.05 (Fisher protected LSD).
204
JOURNAL
OF ECONOMIC
Vol. 91, no. 1
ENTOMOLOGY
TobIe 5. Instar toxicity rotios of various larval instars of a susceptible laboratory strain of tufted apple bud lItoth exposed to seleeted inseclidde~ through diet incoq)oralion
Time of mortality
Chemical
Azinphosmethyl
35 WP
Hexaflllmuron 5% EC
Tebllfenozide 2 F
Abamectin 0.15 EC
Fenoxycarb 25 WP
Toxicity ratio 3rd/neonateb
5th/3rd,1
5th I neonate"
reading,a
LC50
Range
LC50
Range
LC50
Ran~e
7 14 AE 7 14 AE 7 14 AE 7 14 AE 7 14 AE
S9.6* 72.4* 140.3*
59.8-126 52.7-99.4 81.9-240
]09.6* 65.S* 122.1
72.7-]65 46.2-93.6 70.7-211
1.3 0.9 0.9
0.9-1.9 0.7-1.2 0.7-1.1
0.4* 1.2 4.9* 3.9* 18.2* 172* 19.7* 2.8*
0.2-0.8 0.8-1.8 3.7-6.6 3.2-4.8 4.8-69.3 80.1-371 12.3-31.3 1.4-5.7
1.6 1.2 4.4* 2.7* 15.2* 127* 46.4* 7.5*
0.8-3.1 0.7-1.8 3.4-5.7 2.0-3.5 4.0-57.4 41.6-388 29.0-74.3 3.7-15.0
4.0* 1.0 0.9 0.7* 0.8 0.7 2.4* 2.6
1.8-8.9 0.7-1.5 0.7-1.2 0.5-0.9 0.6-1.1 0.2-2.6 1.5-3.7 1.0-7.0
0.005* 0.002-0.016
*, si!\nificant at the 95% level (Robertson and Priesler 1992). Mortality observations were made 7 and 14 d after initial exposure and at adult eclosion (AE). /, LCw of 3rd instar/LC50 of neonate larvae. "LCso of 5th instarl LC50 of neonate larvae. d LC50 of 5th instar/LC50 of 3rd instar.
a
compound was 20-172 times less effective than to neonates, but by adult eclosion, additional delayed mortality resulted in a difference of only 3-8 times in susceptibility. Abamectin was only slightly less effective on 5th instars than on 3rds. Fenoxycarb was totally ineffective on neonates given a 14-d exposure period and was 200 times less effective on 3rd than on 5th instars. Discussion Travis et al. (1981), using 24-h topical bioassays on field-collected larvae, found a more gradual increase in the tolerance of tufted apple bud moth larvae to azinphosmethyl as they developed to larger instars. They reported that azinphosmethyl was =55 times more toxic to neonates than to 5th instal'S, but it was only 8.5 times more toxic to neonates than to 3rd instars. Third instars in their study were 6.5 times more susceptible to topically applied azinphosmethyl than were 5th instars. Wells et al. (1983) also evaluated the susceptibility of all tufted apple bud moth instars to azinphosmethyl through 24-h topical bioassays of field-collected larvae. They found the same gradual increase in tolerance as the larvae developed to later instars and reported that neonates were 75 times more susceptible than 5th instars and 10.5 times more susceptible than 3rd instars. Like the Travis et al. (1981) study, they also found an increase of 7.1 times in tolerance between 3rd and 5th instars. A recent 7-d diet incorporation bioassay with field-collected larvae has shown neonates in orchards from Adams County, Pennsylvania, to be 40 times more susceptible than 3rd instars (D.J.B., unpublished data), whereas 5th instars were not evaluated.
The differences in the instar toxicity ratios between the Travis et al. (1981) and Wells et al. (1983) studies and this diet incorporation bioassay may be caused by differences in the strains tested or to differences in the method of exposure. Azinphosmethyl tolerance between instars may increase more gradually in field-collected larvae than in the susceptible laboratory strain because enzymatic detoxification levels are already present at higher levels in the resistant field populations (Carlini et al. 1991), as is suggested by the 20-fold level of resistance (Biddinger et al. 1996). Penetration through the larval cuticle is probably a more important factor in resistance in topical bioassays than in diet incorporation bioassays. The 6.5-fold and 7.l-fold differences in stage susceptibility between 3rd and 5th instars in the Travis et al. (1981) and the Wells et al. (1983) studies, respectively, may be caused by the thicker larval cuticle of 5th instars. The diet incorporation bioassay, however, may indicate that metabolic detoxification of azinphosmethyl does not significantly increase in laboratory-susceptible larvae after the 3rd instar. Wells et al. (1983) did, however, find increased levels of glutathione S-transferase activity and decreased levels of azinphosmethyl activation to its toxic oxygen analog in 5th instars when compared with 3rd instars. This would indicate an enzymatic basis for susceptibility differences between larval instars that this bioassay with a susceptible strain would probably not detect. Accurate measurement of the significance of these metabolic resistance mechanisms, however, would be better evaluated by ingestion studies than by topical assays because P. idaeusalis larval mortality in the field is caused by both ingestion and contact activity. Results from this study indicate that if azin-
February 1998
BIDDINGER ET AL.: STAGE SPECIFICITY OF INSECTICIDES TO P.
ph osmethyl is to be used effectively in the field to control tufted apple bud moth, applications must be directed toward the susceptible neonates. Because tufted apple bud moth is also resistant to many commonly used organophosphate insecticides besides azinphosmethyl (Knight and Hull 1989b) and because many of these same compounds also appear to become less effective on tufted apple bud moth larvae as they develop (Travis et al. 1981, Rock and Shaltout 1983), the timing of organophosphate applications for hatching neonates becomes even more critical. Also, because most apple growers in Pennsylvania apply pesticides by the alternate-row middle method (Hull et a\. 1983), organophosphate sprays optimally timed for 1st egg hatch predominantly impact only early-instar tufted apple bud moth on the sprayed side of the tree. Knight and Hull (1992a, b) showed that larvae on the unsprayed side of the tree receive only 9 -22% of the insecticide dose on the sprayed side of the tree. Therefore, by the time the 2nd alternate-row middle application is completed 7-10 d later, many of the larvae have subsequently developed to the much more tolerant 3rd instars. The results of this research has led to a change in the recommended application method from alternate-row middle to a both-side application for the initial spray at 1st egg hatch if only organophosphate insecticides are used (Biddinger et al. 1993). Timing of organophosphate insecticides for 1st egg hatch is still considered optimal for control because this period generally coincides with peak egg deposition and many organophosphates, including azinphosmethyl, possess excellent ovicidal activity as well (Travis et al. 1981, Table 4). The chitin synthesis inhibitor hexaflumuron was the only compound evaluated that was, in genera\, equally effective on all instars. Some studies with chitin synthesis inhibitors have indicated that early instars are the most susceptible stage for some Lepidoptera (Retnakaran and Wright 1987). Other studies have shown treatment of later instars to be more effective, if mortality is assessed later in development to include the often lethal abnormal morphological effects these compounds cause in pupae and adults (Retnakaran and Smith 1975, Granett and Retnakaran 1977, Madore et at. 1983, Gaaboub et aJ. 1985). The lack of stage specificity with hexaflumuron in this study, despite multiple mortality readings which included these delayed mortality effects, is therefore somewhat surprising. To control tufted apple bud moth successfully in the field, however, this lack of specificity may be an advantage in that the timing of applications for a critical stage is not necessary. Applications via the alternate-row middle method coupled with the excellent ovicidal activity of this compound (Table 4) would allow this compound to be used against any tufted apple bud moth stage except the pupae or adults. Field trials have shown hexaHumuron to be fairly effective in controlling tufted apple bud moth (Hull 1987, Hull and Barrett 1990b), but develop-
idaeusalis
205
ment of this compound in the United States was terminated in 1991. The ecdysone agonist tebufenozide was more specific to neonates than to later instars (Table 5). Approximately 18 and 15 times more material was required to kill 50% of the 3rd and 5th instars, respectively, by adult eclosion than was needed to kill neonates. However, this specificity toward neonates may not be functionally important in the field at the suggested rate of 92 ppm because of the extreme toxicity of this compound to both resistant and susceptible strains of tufted apple bud moth (Biddinger et at. 1996). Tebufenozide has been shown to be extremely effective in controlling tufted apple bud moth in the field (Hull and Barrett 1990a, b; Biddinger and Hull 1991; Biddinger 1993) and Barrett and Hull (1990) reported excellent activity for at least 28 d using a field residual bioassay. Although this compound had fair ovicidal activity at the highest rate in the laboratory, it appears to be much more effective in controlling tufted apple bud moth larvae in the field (Biddinger 1993). Abamectin killed neonate tufted apple bud moth more quickly than older larvae. Abamectin is an agonist of the inhibitory neurotransmitter GABA at the neuromuscular junctions of insects (Lasota and Dybas 1991). Although it causes paralysis within 7 d, the larvae often remain alive but immobile for several days until they starve (Mellin et al. 1983, Deecher et aI1990). The later instars in this study probably required more time to starve than the neonates and thus were not assessed as dead until the 14-d or adult eclosion readings. When mortality was assessed for the later instars at adult eclosion, only 3-7.5 times as much abamectin was required to kill 3rd and 5th instars than neonates and it was equally effective on 3rd and 5th instars. Robertson et al. (1985) tested 3rd- 6th instars of the western spruce budworm, Choristoneura occidentalis Freeman, and found that the larger 5th and 6th instars were significantly more susceptible (>2 times) to abamectin than were 3rd instars when fed treated foliage and mortality was evaluated at adult eclosion. Neonates were not evaluated for comparison in their study. Abamectin was relatively ineffective as an ovicide on tufted apple bud moth. Robertson et a\. (1985), however, found delayed mortality in larvae from freshly laid western spruce budworm eggs that had been treated with abamectin. Whether this larval mortality was caused by ovicidal activity or from lethal effects of surface residues as the larvae hatched was unclear. Abamectin residues on the surface of leaves are quickly broken down by sunlight (half-life in water of 12 h), but against mite pests this compound has been shown to give residual control for over 21 d by translaminar movement into leaf tissues (Lasota and Dybas 1991). It has yet to be determined if this translaminar activity will effectively increase the residual life of abamectin to lepidopteran pests such as tufted apple bud moth. Although a short residual life may be an advantage for a compound in pre-
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venting the development of resistance, it may be a disadvantage in an alternate-row middle application scheme, since multiple applications would be needed toward instars of various ages. In addition, multiple applications of abamectin would be disruptive to integrated mite control programs because of its miticidal activity. Multiple applications during the season could lead to the rapid development of mite resistance. Field trials have shown abamectin to be an effective miticide on apples (L.A.H., unpublished data), but very toxic to S. p. punctum and relatively ineffective for control of tufted apple bud moth (Biddinger and Hull 1995). Fenoxycarb was the most stage-specific compound tested. It had no effect on neonates that were exposed for 14 d and was 200 times more effective on 5th instars than on 3rd instars. The relative titers of juvenile hormone and the molting hormone 20hydroxyecdysone are extremely important during the larval-pupal transformation in last instars, and excess levels of a juvenile hormone mimic can cause potentially lethal abnormalities during this critical developmental event (Staal 1975, Blum 1985). Mauchamp et al. (1989) used radiolabeled fenoxycarb to show that it was eliminated from the bodies of 4th- and 5th-instar tobacco budworm (H. virescens) within 3-5 d after ingestion. If larvae can eliminate fenoxycarb quickly from their bodies, then 3rd instar tufted apple bud moth exposed to fenoxycarb for only 14 d would probably have eliminated most of the compound from their bodies before initiating the molt to the pupal stage. The same would be true for neonate tufted apple bud moth because they would have developed to only 3rd instars during the 14-d exposure period and therefore would have completely eliminated fenoxycarb from their bodies by the time of the critical larval-pupal molt. This hypothesis would explain why fenoxycarb was very toxic to 5th instars, relatively ineffective on 3rd instars, and had no effect on neonates in this study. Fenoxycarb has shown good larvicidal activity toward late instars in the field (Hull et al. 1991a, Biddinger 1993). Fenoxycarb demonstrated very good ovicidal activity in the laboratory, even at the low 1/l0X rate. Hull et al. (1991b), however, found little ovicidal activity with fenoxycarb in the field. Fenoxycarb has been reported to be effective against eggs laid singly but ineffective against eggs laid in masses, as in tufted apple bud moth, because of a reduction in contact between eggs and concentrated residues on the treated leaf surface (Charmillot et al.1985, Hull et al. 1991a). The greater efficacy offenoxycarb on tufted apple bud moth egg masses in this study is probably caused by the increased coverage and contact the immersion method allowed. The ovicidal study provided a preliminary indication of the activity of these compounds toward tufted apple bud moth egg masses. A more realistic measurement of the ovicidal activity could be achieved by spraying apple foliage and allowing tufted apple bud moth females to oviposit eggs on
Vol. 91, no. 1
pre-existing residues or to spray eggs of varying ages on apple foliage by a method more comparable to concentrate airblast applications in the orchard (i.e., Potter spray tower). For example, Elliot and Anderson (1982a, b) showed that the ovicidal activity of the chitin synthesis inhibitor diflubenzuron was strongly correlated with the age of eggs of codling moth, Cydia pomonella (L.), at application, and that the addition of surfactants to improve penetration and coverage could significantly improve ovicidal activity. The organophosphate and carbamate insecticides currently registered on apple have a relatively short residual activity «10 d) (Knight and Hull 1992a, b) and are recommended starting at egg hatch for both tufted apple bud moth generations (Biddinger et al. 1993). An advantage some IGRs have over these compounds is their much longer residual activity. Fenoxycarb is known to have good larvicidal field activity toward tufted apple bud moth for 21-28 d (Hull et al. 1991a), and tebufenozide has given outstanding control of neonate tufted apple bud moth 28 d after application (Hull and Barrett 1990c). The residual activities for the chitin synthesis inhibitor IGRs and abamectin are not known for tufted apple bud moth. Longer residual activity could make application timing of stage-specific compounds less critical. As long as the materials are applied before the insect reaches the sensitive stage, growers could have more freedom to apply persistent insecticides when time constraints allow or when weather conditions or fungicide programs permit. The longer residual activity of some of these compounds also could greatly reduce the current number of organophosphate and carbamate applications from 6 to 7 during the season. Unfortunately, the longer residual activity of some insect growth regulators also could accelerate the development of resistance because of the constant selection pressure to all life stages during development. The development of a management program using fenoxycarb may be more difficult because of its stage specificity. Only a single application per tufted apple bud moth brood probably would be required for fenoxycarb because of its residual activity of up to 28 d (Hull et al. 1991a). Despite its activity in the laboratory, this compound does not appear to be very effective as an ovicide in the field (Hull et al. 1991b). Therefore, fenoxycarb applications would have to be timed for late instars. To control late instars of the summer brood, fenoxycarb would have to be applied in July at a time when S. p. punctum populations usually begin to build. Fenoxycarb is know to be toxic to last-instar larvae, pupae, and eggs of S. p. punctum in the field and laboratory, which could curtail its commercial acceptance (Biddinger and Hull 1995) .Tufted apple bud moth larvae are known to enter leaf shelters as 3rd instars to complete development, but it is not known to what extent they feed outside of the shelters or if they create successive shelters during development. If they remain in the shelter until pupation, 4th- or
February
1998
BIDDINGER
ET AL.: STAGE SPECIFICITY
5th-instar tufted apple bud moth would be relatively proh'cted from fenoxycarb applications. Applications would therefore have to be made before the 3rd instars create shelters. Control of the overwintering generation of tufted apple bud moth might be less complicated. Fenoxycarb could be applied to overwintering larvae in the orchard groundcover with a herbicide sprayer to control late instars early in the spring (Felland and Hull 1991). Successful control of tufted apple bud moth using fenoxycarb will be dependent not only upon the direct action of the compound, but also from the sublethal effects on the reproductive system of adults issuing from larvae that survive exposure (Robertson and Kimball 1979). Compounds such as tebufenozide, hexaflumuron, and abamcctin, which are most effective on early instars, could be more easily integrated into tufted apple bud moth control programs similar to the current organophosphatecarbamate programs. Initial applications would probably be timed for 1st egg hatch, and the need for subsequent applications within each brood would be dependent on their residual activity or effectiveness. With a compound like hexaflumuron, which appears to possess both ovicidal and nonstage-specific larvicidal activity, growers could initiate tufted apple bud moth control at 1st egg hatch and use alternate-row middle sprays to control larvae through the 3rd instar if necessary. Since the residual activity of hexaflumuron toward tufted apple bud moth is unknown, the need for multiple applications per brood is also unknown. Tebufenozide was somewhat more stagespecific toward early instars, but not nearly as ovicidal as hexaflumuron in the laboratory. Its long residual activity has allowed for excellent control of tufted apple bud moth in the field with only 1 complete application per brood (Biddinger 1993, Hull 1995). The main constraint in controlling tufted apple bud moth with these 2 compounds would be to ensure that larvae were exposed before becoming 3rd instars, because the leafrolling habit possessed by 4th and 5th instars might protect them from spray residues. Major constraints in the use of abamectin for tufted apple bud moth control would be its extremely short residual activity and specificity toward early instars, which would make it unsuitable for alternate-row middle applications. Also, multiple applications of this compound would be disruptive to mite control because of its miticidal activity and its toxicity to S. p. punctum.
Acknowledgments Wl' p;ratt'fully acknowledge Gary Wilson, Emily Lott, and Mike Trimmer for their assistance in data collection and colony maintenance. We also thank Jim Travis, and Diana Cox-Foster for their review of an early draft of this manuscript and Rohm and Haas Company for financial support of this project.
OF INSECfICIDES
TO
P. idaeu.salis
References
207
Cited
Abacus Concepts. 1989. Accessible general linear modeling. Abacus Concepts, Berkeley, CA. Barrett, B. A., and L. A. Hull. 1990. Residual activity of insect growth regulators, 1989, pp. 371-372. III Insecticide and aearicide tests, vol. 15. Entomolop;ical Society of America, Lanham, MD. Biddinger, D. J. 1993. Toxicity, stage specificity, and sublethal effects of abamectin and several classes of insect growth regulators to Platynota idacusalis (Lepidoptera: Tortricidae) and Stcthorus )Junctum (Coleoptera: Coccinel1idae) Ph.D. dissertation, Pennsylvania State University, University Park. Biddinger, D. ]., and L. A. Hull. 1991. Apple, evaluation of IGRs for tufted apple bud moth control, 1990, pp. 3- 4. In Insecticide and acaricide tests, vol. 16. Entomological Society of America, Lanham, MD. 1995. Effects of several types of insecticides on the mite predator, Stethorus )Junctum (Coleoptera: Coccincl1idae), ineIuding insect growth regulators and abamcetin. J. Econ. Entomol. 88: 358-366. Biddinger, D. J., L. A. Hull, and C. M. Felland. 1993. Tufted apple bud moth control is getting more complicated! Penn. Fruit News 73(4): 87-94. Biddinger, D. J., L. A. Hull, and B. A. McPheron. 1996. Cross-resistance and synergism in azinphosmethyl resistant and susceptible strains of tufted apple bud moth (Lepidoptera: Tortricidae) to various insect growth regulators and abamectin. J. Econ. Entomol. 89: 274287. Blum, M. S. [ed.]. 1985. Fundamentals of insect physiology. Wiley, New York. Bull, D. L. 1986. Toxicity and pharmacodynamics of avermectin in the tobacco budworm, corn earworm, and fall armyworm (Noctuidae: Lepidoptera). J. Ap;rie. Food Chem. 34: 74-78. Carlini, E. J., B. A. McPheron, C. M. }'elland, and L. A. Hull. 1991. Elevated esterase activity in resistant tufted apple bud moth, Platynota idaeltSalis (Walker) (Lepidoptera: Tortricidae). Compo Biochem. Physio!. 99C: 375-377. Charmillot, P. J., K. Vernez, B. B\oesch, M. BeITet, and P. Pasquier. 1985. Ovicidal effect of fenoxycarb, and insect growth regulator, on four tortricid species harmful to vineyards and orchards. Mitt. Schweiz. Entomol. Ges. 58: 393-399 (in French). David, P. J., and R. L. Horsburgh. 1985. Ovicidal activity of methomyl on eggs of pest and beneficial insects and mites associated with apples in Virginia. J. Econ. Entomol. 78: 432-436. Deecher, D. C., J. Brezner, and S. W. Tanenbaum. 1990. Sublethal effects of avermectin and milbemycin on the gypsy moth (Lepidoptera: Lymantriidae). J. Econ. Entomol. 83: 710-714. Elliot, D. W., and R. H. Anderson. 1982a. Efficacy of di£lubenzuron against the codling moth I.a.\'peyresia )Jomonella (Lepidoptera: Olethreutidae), and impact on orchard mites. Can. Entomol. 114: 733-737. 1982b. Factors influencing the activity of difluben7.llron against the codling moth Laspeyresia pomonella (Lepidoptera: Olethreutidae). Can. Entomol. 114: 2159-268. Felland, C. M., and L. A. Hull. 1991. Tufted apple bud moth greenhouse ground cover test, 1990, p. 291. III Insecticide and Acaricide Tests, vol. 16. Entomolop;ical Society of America, Lanham, MD. Gaaboub, I. A., M. S. El-Helaly, and S. M. Moustafa. 1985. Food utilization, rate oflarval growth, and fecundity of Bombyx mori L. (Lepidoptera: Bombycic1ae) fed mul-
208
JOURNAL
OF ECONOMIC
berry leaves treated with methoprene, triprene, and diflubenzuron. J. Econ. Entomol. 78: 1182-1186. Gmnett, J., and A. Retnakaran. 1977. Stadial susceptibility of eastern spruce budworm, Choristoneura fumi.f emna (Lepidoptera: Tortricidae), to the insect growth regulator Dimilin. Can. Entomol. 109: 893-894. Hull, L. A. 1987. Apple, dilute test of insecticides, 1986, pp. 24-28. In Insecticide and acaricide tests, vol. 13. Entomological Society of America, Lanham, MD. 1995. Apple, tufted apple bud moth management tactics, 1994, pp. 24-28. In Arthropod management tests, vol. 20. Entomological Society of America, Lanham, MD. Hull, L. A., and E. H. Beers. 1985. Ecological selectivity: modifying chemical control practices to preserve natural enemies, pp. 103-122. In M. A. Hoy and D. C. Herzog [eds.], Biological control in agricultural IPM systems. Academic, New York. Hull, L. A., and A. L. Knight. 1989. Effect of late-season fen valerate and f1ucythrinate applications on European red mite (Acari: Tetranychidae) and tufted apple bud moth (Lepidoptera: Tortricidae) populations on apple. J. Econ. Entomo\. 84: 1174-1179. Hull, L. A., and B. A. Barrett. 1990a. Evaluation of insect growth regulators for leafroller control, 1989, pp. 2223. In Insecticide and acaricide tests, vol. 15. Entomological Society of America, Lanham, MD.. 1990b. Seasonal dilute insecticide experiment, 1989, pp. 26 -28. In Insecticide and acaricide tests, vol. 15. Entomological Society of America, Lanham, MD. 1990c. Residual activity of IGRs, 1989, pp. 371-372. In Insecticide and acaricide tests, vol. 15. Entomological Society of America, Lanham, MD. Hull, L. A., K. D. Hickey, and W. W. Kanour. 1983. Pesticide usage patterns and associated pest damage in commercial orchards of Pennsylvania. J. Econ. Entomol. 76: 577-583. Hull, L. A., B. A. Barrett, and E. G. Rajotte. 1991a. Foliar persistence and effects of fenoxycarb and Platynota idaeusa/is (Lepidoptera: Tortricidae) on apple. J. Econ. Entomol. 84: 965-970. Hull, L. A., E. G. Rajotte, and D. J. Biddinger. 1991b. Apple, evaluation of foliar-applied insect growth regulators for leafroller control, 1990, pp. 15-16. In Insecticide and acaricide tests, vol. 16. Entomological Society of America, Lanham, MD. Knight, A. L., and L. A. Hull. 1989a. Use of sex pheromone traps to monitor azinphosmethyl resistance in Platynota idaeusalis (Lepidoptera: Tortricidae). J. Econ. Entomol. 82: 1019-1026. 1989b. Response of tufted apple bud moth (Lepidoptera: Tortricidae) neonates to selected insecticides. J. Econ. Entomol. 82: 1027-1032. 1992a. Linking insecticide bioassays with residue analyses to evaluate control of Platynota idaeusalis (Lepidoptera: Tortricidae) neonates on apple: I. single spray. J. Econ. Entomol. 85: 926-931. 1992b. Linking insecticide bioassays with residue analyses to evaluate control of Platynota idaeusalis (Lepidoptera: Tortricidae) neonates on apple: II. seasonal spray program. J. Econ. Entomol. 85: 932-938.
ENTOMOLOGY
Vol. 91, no. 1
Lasota, J. A., and R. A. Dybas. 1991. Avermectins, a novel class of compounds: implication for use in arthropod pest contro\. Annu. Rev. Entomol. 36: 91-117. LeOra Software. 1987. POLO-PC. A user's guide to probit or logit analysis. Berkeley, CA. Madore, C. D., D. G. Boucias, and J. B. Dimond. 1983. Reduction of reproductive potential in spruce budworm (Lepidoptera: Tortricidae) by a chitin-inhibiting insect growth regulator. J. Econ. Entomol. 76: 708 -710. Mauchamp, B., C. Malosse, and P. Saroglia. 1989. Biological effects and metabolism of fenoxycarb after treatment of the fourth and the fifth instars of the tobacco budworm, Heliothis virescens F. Pestic. Sci. 26: 283-301. Meagher, R. L., Jr. 1985. Spatial patterns, predictive sampling, and techniques to measure azinphosmethyl resistance of Platynota idaeusalis (Walker) (Lepidoptera: Tortricidae). Ph.D. dissertation, Pennsylvania State University, University Park. Mellin, T. N., R. D. Busch, and C. C. Wang. 1983. Postsynaptic inhibition of invertebrate neuromuscular transmission by avermectin Bla. Neuropharmacology 22: 89-96. Retnakaran, A., and L. Smith. 1975. Morphogenetic effects of an inhibitor of cuticle development on the spruce budworm, Choristoneura fumerana (Lepidoptera: Tortricidae). Can. Entomol. 107: 883-886. Retnakaran, A., and J. E. Wright. 1987. Control of insect pests with benzoylphenyl ureas. pp. 205-282. In J. E. Wright and A. Retnakaran [eds.], Chitin and benzoylphenyl ureas. Junk, Dordrecht. Robertson, J. L., and R. A. Kimball. 1979. Effects of insect growth regulators on the spruce budworm (Chotistoneum occidentalis) (Lepidoptera: Tortricidae) II. Fecundity and fertility reduction following last instar treatments. Can. Entomo\. 111: 1369-1380. Robertson, J. L., and H. K. Preisler. 1992. Pesticide bioassays with arthropods. CRC, Boca Raton, FL. Robertson, J. L., C. E. Richmond, and H. K. Preislet". 1985. Lethal and sublethal effects of averrnectin Bl on western spruce budworm (Lepidoptera: Tortricidae). J. Econ. Entomol. 78: 1129-1132. Rock, G. C., and A. D. Shahout. 1983. Toxicities of three synthetic pyrethroids and selected orchard insecticides to the tufted apple bud moth, Platynota idaeusll/is (Lepidoptera: Tortricidae). J. Econ. Entomol. 76: 1384-1389. Staal, G. B. 1975. Insect growth regulators with juvenile hormone activity Annu. Rev. Entomol. 20: 417-460. Travis, J. W., D. Asquith, and P. D. Mowery. 1981. Bioassay study of commercial formulations of several insecticides on Platy nota idaeusa/is. J. Econ. Entomol. 74: 328-330. Wells, D. S., G. C. Rock, and W. C. Dallterman. 1983. Studies on the mechanisms responsible for variable toxicity of azinphosmethyl to various larval instars of the tufted apple bud moth, Platynota idaeusalis. Pestic. Biochem. Physiol. 20: 238-245. Received for publication 21 May 1996; accepted 4 August 1997.
