aQueensland Department of Primary Industries, Maroochy Horticultural Research Station, Nambour,. 4560 Qld., Australia blntegrated Pest Management Pty.
Experimental & AppliedAcarology, 12 ( 1991 ) 195-217
195
Elsevier Science Publishers B.V., Amsterdam
Studies of the predatory mite Amblyseius victoriensis (Acarina: Phytoseiidae) in citrus orchards in south-east Queensland: control of Tegolophus australis and Phyllocoptruta oleivora (Acarina: Eriophyidae ), effect of pesticides, alternative host plants and augmentative release D. S m i t h a a n d D . F . P a p a c e k b aQueensland Department of Primary Industries, Maroochy Horticultural Research Station, Nambour, 4560 Qld., Australia blntegrated Pest Management Pty. Ltd., 28 Orton Street, Mundubbera, 4626 Qld., Australia (Accepted 6 March 1991 )
ABSTRACT Smith, D. and Papacek, D.F., 1991. Studies of the predatory mite Amblyseius victoriensis (Acarina: Phytoseiidae) in citrus orchards in south-east Queensland: control of Tegolophus australis and Phyllocoptruta oleivora (Acarina: Eriophyidae), effect of pesticides, alternative host plants and augmentative release. Exp. AppL Acarol., 12:195-217. Seasonal history studies and a pesticide disruption trial showed that the Australian phytoseiid Amb!yseius victoriensis (Womersley) was a very effective predator of the native eriophyid Tegolophus australis Keifer, in commercial citrus orchards at Gayndah and Mundubbera, Queensland, from 1984 to 1990. Amblyseius victoriensis numbers rose from 10-20 per 100 leaves in spring to 100 or more per 100 leaves in mid summer, keeping the percentage of T. australis-infested fruit well below an economic threshold of 10%. However, in the same orchards, A. victoriensis only controlled the cosmopolitan eriophyid Phyllocoptruta oleivora (Ashmead), when less than 5% of the fruit was infested with the pest and predator numbers exceeded 40 per 100 leaves. Aspects of orchard management influencing populations ofA. victoriensis, were evaluated. The pesticides benomyl, dicofol, mancozeb, methidathion, and mezineb reduced populations by 100%, methomyl by 89%, chlorpyrifos by 80%, fenbutatin oxide by 42.5% and endosulfan by 27.5%. Iprodione and hydrated lime caused a 17% reduction, but copper oxyehloride and narrow-range oil had little effect. Encouragement of alternative host plants in the orchard increased populations ofA. victoriensis. Where Rhodes grass, Chloris gayana Kunth, was allowed to flower in the inter-rows, its windblown pollen served as a supplementary food source. Windbreak rows of Eucalyptus torelliana F. Muell. acted as reservoirs of A. victoriensis for nearby blocks of citrus. Augmentative release was efl'ective for re-establishing A. victoriensis where it was absent following pesticide suppression.
0 168-8162/91/$03.50 9 1991 Elsevier Science Publishers B.V. All rights reserved.
196
D. SMITH AND D.F. PAPACEK
INTRODUCTION
The brown citrus rust mite, Tegolophus austral& Keifer, and the citrus rust mite, Phyllocoptruta oleivora (Ashmead), are serious pests in the main citrusgrowing areas of Queensland at Gayndah and Mundubbera (approximately 25.5~ 152~ Smith and Papacek, 1985). Tegolophus australis commonly occurs in Queensland and New South Wales and, to a much lesser extent, in citrus along the Murray River and in the Murrumbidgee Irrigation Area. It is thought to be a native species originating on five species of native Microcitrus in coastal areas and on the desert lime Eremocitrus glauca (Lindl.) Swingle in subcoastal areas. Tegolophus australis prefers the more exposed parts of the fruit and the upper leaf surfaces. Phyllocoptruta oleivora, a cosmopolitan species, occurs in coastal and subcoastal areas of Queensland and New South Wales. Hot dry conditions are detrimental to P. oleivora, and it prefers the less-exposed parts of the fruit and the lower leaf surfaces. Both species can occur together, or one may dominate. Historically, they have been controlled with up to four miticide applications per season. Since 1979, integrated pest management (IPM) has been increasingly used for a wide range of pests occurring in Queensland citrus, with control of scales and mealybugs by parasitoids a major component (Smith and Papacek, 1985 ). Effective biological control of rust mites was first observed in 1979, when the use of organo-phosphates was discontinued in a 350-ha orchard at Mundubbera (Smith and Papacek, 1984). The predator responsible was Arnblyseius victoriensis (Womersley), a native species occurring widely in most eastern states of Australia on a wide range of introduced and native vegetation (Schicha, 1987; James, 1989a). Pest monitoring has been an important component of IPM since its inception in Queensland citrus. Orchards are sampled fortnightly, and information collected includes the percentage of fruit infested with T. australis and P. oleivora and the number of A. victoriensis per 100 leaves. Miticides (e.g., fenbutatin oxide at 0.1-0.2 g a.i. L - 1) are applied when 10% or more of the fruit is infested with either pest species. This threshold is lifted to 20% for T. australis if there are 40 or more A. victoriensis per 100 leaves (Broadley et al., 1987). This paper reports studies evaluating the ability ofA. victoriensis to control T. australis and P. oleivora and three aspects of orchard management influencing A. victoriensis numbers, viz. the effect of commonly used pesticides in Queensland citrus, the use of alternative plant hosts to stimulate populations and the use of augmentative releases to re-establish the predator following disruptive pesticide application. METHODS
Efficacy As part of a commercial scouting service in the Gayndah-Mundubbera area,
197
STUDIES OF AMBLYSE1US: CONTROL OF TEGOLOPHUS AND PHYLLOCOPTRUTA
each year from 1984 to 1990, an average 268 blocks (each 0.5-5 ha) of various varieties of citrus (mainly Washington Navel and Late Valencia oranges, F,Uendale, Imperial, Murcott and Hickson mandarins, Lisbon lemons and Marsh grapefruit) were monitored for a range of pest and beneficial insects (Table 1 ). Monitoring was fortnightly from October to harvest (April to August, depending on the variety ). The data collected included an assessment of the percentage-of mite-infested fruit and the numbers of A. victoriensis per 100 leaves. Five random fruit within reach on 20 random trees per block were examined with a hand-lens ( • 10 magnification) looking at 5 cm 2 on the exposed and sheltered sides of each fruit to record the pest mite species present. The area examined represented one field of view of the handlens. In four of the 20 trees monitored (for trees 4 m or higher), the fruit samples were selected from the top centre of the tree (where spray coverage tended to be poorest). These tree-top samples were mainly to detect scale infestations; mite numbers did not vary significantly from samples lower down. The best sampling site for A. victoriensis was the leaves, and a small twig from just inside the outer canopy (avoiding very old and very young foliage ) was plucked from each of the 20 random trees; the number of predators (adults and/or juveniles) on the first five leaves were recorded. Amblyseius victoriensis rests on the undersurface of the leaves, leaving only to search for food or water and oviposits on or near the resting sites. This is common behaviour in phytoseiids (Overmeer et al., 1982). Table 1 lists pesticide use on the monitored blocks. A total of 275 blocks (over the six seasons) received a minimum of pesticides, viz. one or two copper oxychloride or copper hydroxide applications in early October and/or mid November for routine fungal disease control, and bait applications to the TABLE 1
Citrus blocks monitored for mites A victoriensis (A.v.), T. australis (T.a.) and P. oleivora (P.o.) and pesticide applications from 1984 to 1990 Year
1984-85 1985-86 1986-87 1987-88 1988-89 1989-90
Total Mean
Pesticide application: No. of blocks with % of blocks with blocks Mancozeb and/or Other: e.g., monitored A.v. T,a. P.o. T.a. +P.o. Only copper oxychloride methidathion endosulfan, fenbutatin oxide and/or bait No. of
232 276 258 264 287 300 1617 268.2
54.3 74.1 44,3 89.1 76.1 69.9 70.2 36.8 30.8 79.5 5.7 4.8 70.7 0.3 0.2 71.7 0.3 0.2
21 58 15 41 10 130
123 83 129 125 202 103
2ll 218 243 223 277 170
77.5 73.0 30.0 80.3
275 46
332 55
1342 224
70.7 92.0 65.7 77.3 80.5 77.7
198
D. SMITH AND D.F. PAPACEK
tree skirts in the a u t u m n for Queensland fruit fly, Batrocera tryoni Froggatt, on early varieties. Observation prior to 1984 indicated that both of these treatments had minimal effect on A. victoriensis, 7". australis and P. oleivora (Smith and Papacek, 1985 ). Data for the efficacy ofA. victoriensis against T. australis and P. oleivora was taken almost exclusively from these blocks. Six 12-year-old Ellendale mandarine trees in a small 0.25-ha block were randomly selected for a pesticide disruption trial onA. victoriensis during 1985. Three of the trees were sprayed on 11 March and again on 24 April with methidathion to suppress A. victoriensis. The spray was applied with an oscillating boom delivering 30 L of spray per tree. Each of the six trees were surrounded by guard trees to minimize spray drift. Numbers of T. australis were recorded at fortnightly intervals in a r a n d o m 10-cm 2 section of the upper leaf surface of 50 leaves per tree. Also, the numbers ofA. victoriensis present on 100 leaves (20 twigs each with five leaves) were recorded.
Effect of pesticides The remaining blocks received varying levels of pesticides applied with an oscillating boom at up to 11 000 L per ha affecting either A. victoriensis a n d / or the pest mites. For example, in 1987-88 (Table 1 ), of a total of 264 blocks, 41 were sprayed only with copper oxychloride a n d / o r bait, 223 were sprayed with endosulfan, fenbutatin oxide or chlorpyrifos and of these 223 blocks, 129 were also sprayed with mancozeb a n d / o r methidathion - - both of which have been observed to be very toxic to A. victoriensis (Smith and Papacek, 1985 ). Data for the effect of pesticides on A. victoriensis was taken from 542 of these blocks during 1986-90. In the remainder, combined use or proximity of use of different pesticides meant the data could not be used. Observations were made in a further 60 blocks on the effect of foliar applications of micronutrients Zn, Mb, Mg, Mn, B and KNO3, and of the fruit thinner ethrel.
Use of alternative host plants During 1986-87, the numbers ofA. victoriensis on eight 25-year-old Ellendale mandarin blocks in two orchards were compared. In one orchard there was heavy inter-row growth of Rhodes grass, Chloris gayana, which was mowed infrequently (3-monthly intervals) and was continually in flower. In the other, the inter-rows were mowed every 7-10 days. Both orchards were unsprayed except for a copper oxychloride spray in October for routine fungal disease control. During 1987-88, numbers of A. victoriensis in two 15-year-old Imperial mandarin blocks were compared. One block was adjacent to a windbreak of 10-m-high Eucalyptus torelliana F. Muell., while the other was (at its nearest
STUDIES OF AMBLYSEIUS: CONTROL OF TEGOLOPHUS AND PHYLLOCOPTRUTA
199
point) 400 m away in the middle of the orchard. The A. victoriensis numbers on the eucalypt trees were assessed by counting predators on 20 randomly selected leaves on ten trees at fortnightly intervals. Both Imperial mandarin blocks had been sprayed with a disruptive pesticide (methidathion) for citrus snow scale, Unaspis citri (Comstock), in early November, and so initial A. victoriensis numbers were low.
Augmentative releases During 1987-88, an augmentative release of A. victoriensis was made in two blocks. The first, 0.5 ha of 10-year-old Ortanique mandarins in four rows of 31 trees per row, was sprayed with chlorpyrifos and fenbutatin oxide in mid November; at the commencement of sampling in late December, there were no T. australis or A. victoriensis present. Amblyseius victoriensis-infested leaves from another site were placed in three trees per row, a total of 12 trees in the block on 29 December 1987. An estimated 75-100 predators were released in each tree. The numbers ofA. victoriensis were counted on 20 leaves of each of the 12 release trees and on 16 non-release trees. Four of the nonrelease trees were adjacent within a row to a release tree, four were one tree removed, four were three trees removed and four were four trees removed. Counts were made at 1-4-week intervals until late June. The second block was 0.5 ha of 15-year-old Ellendale mandarins. The miticide fenbutatin oxide was applied in mid November 1987 to control a heavy infestation of T. australis and, as the rust mite numbers began to increase again, a release of A. victoriensis was made on 18 December using infested avocado, Persea americana Mill, leaves. Twenty leaves were placed in each tree, giving an estimated release of 75-100 mites per tree. Both T. australis and A. victoriensis were assessed usually at fortnightly intervals by the previously described orchard monitoring techniques. RESULTS
Efficacy Table 1 shows the incidence of A. victoriensis, T. australis and P. oleivora during the six seasons 1984-90. Amblyseius victoriensis was a very effective predator of T. australis. Mean percentages of fruit infested with T. australis and numbers of A. victoriensis on three similar 40-year-old Ellendale mandarin blocks in one orchard during 1987-88 are given in Fig. 1. The percentage of fruit infested with T. australis peaked at 6% in mid November, but this yeas reduced to zero by early January as predator numbers rose to 90 per 100 leaves. Most commonly, T. australis was kept at a negligible level from very early
200
D. SMITH
AND D.F. PAPACEK
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D. SMITH AND D.F. PAPACEK
in the season. Figure 2 shows results from 12 similar 40-year-old Ellendale mandarin blocks during 1988-90. The percentage of fruit infested never rose above 1.2%, and predator numbers were above 50 per 100 leaves from early December. Figure 3 shows results from three 20-year-old Washington Navel blocks in one orchard during 1989-90. The early season T. australis infestations were in this case high, 44.7% in early January, but A. victoriensis numbers above 45 per 100 leaves from late January quickly reduced the infestations to zero by late February. Amblyseius victoriensis was effective against P. oleivora only when the initial infestation was low (5% or less fruit infested) and numbers of the predator remained high throughout the season (40 or more per 100 leaves). Mean percentages of fruit infested with P. oleivora and numbers ofA. victoriensis on five similar 15-year-old Late Valencia blocks in one orchard during 1988-89 are given in Fig. 4. The percentage of fruit infested with P. oleivora peaked at 5% in m i d December, but the infestation was contained by predator numbers of 40-100 per 100 leaves from early December on. Figure 5 gives results from a 20-year-old Marsh grapefruit block in 198586, where the initial fruit infestation by P. oleivora (24% rising to 83%) was too high for A. victoriensis to exercise control. Following a. miticide application and continued predator activity (up to 73 per 100 leaves), the P. oleivora infestation remained below 5% until late February. However, in early March when A. victoriensis numbers inexplicably dropped to less than 20 per 100 leaves, the pest mite infestation rose to 12.5% and required a further miticide application. Figure 6 gives results from a Washington Navel orange block in 1985-86, where A. victoriensis numbers again briefly slumped late in the season (from 73 per 100 leaves in m i d January to 14 in early March), and the fruit infestation by P. oleivora rose to 18%. In both cases (in Figs. 5 and 6) the miticide, fenbutatin oxide at 0.2 g a.i. L - ~ was used to control outbreaks. Mean numbers of T. australis and A. victoriensis on three sprayed and three unsprayed trees in the disruption trial are shown in Fig. 7. On sprayed trees, T. australis numbers rose to 119 per 10 cm 2 of leaf surface by early April, and A. victoriensis numbers were severely restricted. Just before the second spray application on 28 April, A. victoriensis numbers increased, and that, combined with increasing rind damage (bronzing) on the fruit, caused a lateseason drop in T. australis numbers. Tegolophus australis numbers on the unsprayed trees fell from 38 per 10 cm 2 of leaf surface on 11 March to less than 5 per 10 cm: by early April. Amblyseius victoriensis numbers on these trees rose from 23 to 100 per 100 leaves. Initial numbers of the predator were low for March because of disruptive spraying with methidathion for citrus snow scale in the spring.
203
STUDIES OF AMBLYSEIUS: CONTROL OF TEGOLOPHUSAND PHYLLOCOPTRUTA
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STUDIES OF AMBLYSEIUS:CONTROL OF TEGOLOPHUSAND PHYLLOCOPTRUTA
207
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Fig. 7. M e a n n u m b e r o f Tegolophus australis per 10 cm 2 o f u p p e r leaf surface a n d AmbIyseius victoriensis per 100 leaves o n Ellendale m a n d a r i n s , 1985, unsprayed a n d sprayed with methidathion.
Effect of pesticides Table 2 shows the effect of an application of commonly used pesticides on numbers of A. victoriensis. The mean percentage drop in numbers per 100 ]eaves is shown together (for some of those pesticides causing a large drop)
D. SMITH AND D.F. PAPACEK
208 TABLE 2
Effect of pesticides on A. victoriensis in a total of 542 blocks from 15 orchards at Gayndah and Mundubbera, 1986-1990 ( 1 ) mean % drop ( + SD) following application in numbers per 100 leaves, (2) mean time of recovery in weeks ( _+ SD) to 20 or more mites per 100 leaves Pesticide
Year 1986/87
Insecticides Chlorpyrifos (1) 0.5ga.i.L-l(2) Endosulfan (1) 0.2 g a.i. L -1 (2) Hydrated lime ( 1 ) 10.0gL -1 Methidathion ( 1 ) 0.5ga.i.L-~(2) Methomyl ( 1 ) 0,05 ga.i. L -1 Narrow range oil ( 1 ) 10.0 g a.i. L -I ) Miticides Dicofol ( 1 ) 0.5 g a.i. L - ' Fenbutatin oxide ( 1 ) 0.2 g a.i. L -~ Fungicides Benomyl ( 1 ) 0.25 ga.i. L - l Copper oxychloride ( 1 ) or copper hydroxide 20.0 g L -I Iprodione (1) 0.25 g a.i. L Mancozeb ( 1 ) 1.6ga.i.L - ~ ( 2 ) Mezineb ( 1 ) 1.6ga.i. L - t
97.8+ 5.9 5.8_+ 1.7 42.1+ 29.4
Mean of the 4 years 1987/88
88.8+ 19.5 5.1_+ 2.1 17.0+_15.0
1988/89
63.5+38.3 2.7_+ 1.1 27.5_+23.9
1989/90
69.3+20.2 2.5+ 0.8 23.7+_18.9
80.2+ 15.8 27.5_+10.5
17.1 + 15,9 100
100
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with the mean time of recovery to 20 or more mites per 100 leaves. Benomyl dicofol, mancozeb, methidathion and mezineb reduced populations by 100%, methomyl by 89.1%, chlorpyrifos by 69.3 to 97.8% (mean 80.2), fenbutatin oxide by 25.2 to 57.5% (mean 42.5), endosulfan by 17 to 42.1% (mean 27.5), iprodione by 16.5%, hydrated lime by 17.1%, narrow-range oil by 1.8% and copper oxychloride or copper hydroxide by 0%. The toxicity of some of the pesticides decreased over time, e.g., chlorpyrifos from 97.8% in 1986-87 to 63.5% in 1988-89, fenbutatin oxide from 57.5% in 1986-87 to 25.2% in 198889, and endosulfan from 42.1% in 1988-89 to 23.7% in 1989-90. With chlorpyrifos, the decrease in toxicity was also demonstrated by the time to recovery - - 6.8 weeks in 1986-87 and 2.7 weeks in 1988-89. Methidathion pre-
209
STUDIES OF AMBLYSEIUS: CONTROL OF TEGOLOPHUSAND PHYLLOCOPTRUTA
vented recovery for 7.7 weeks and mancozeb for 12.8-17.4 weeks. Mancozeb and also mezineb (which are used mainly as disease sprays) were extremely disruptive to A. victoriensis. Table 3 shows mancozeb usage in one Gayndah orchard of 22 blocks during six seasons. Other disruptive pesticides were also sometimes used. Mancozeb (particularly in combination with methidathion ) suppressed A. victoriensis for the whole season, and a heavy miticide programme was necessary to control resulting pest mite infestations, particularly TABLE 3 Mancozeb usage in a Gayndah orchard 1984-90, incidence ofA. victoriensis and mean number of miticides applied to control T. australis (T.a.) and P. oleivora (P.o.) Season
Blocks sprayed Subsequently with Blocks not sprayed Subsequently with Mean no. with mancozeb A. victoriensis with mancozeb A. victoriensis miticides applied
1984-85
0
-
22
22
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5
20
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1985-86
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1987-88
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1988-89
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Fig. 8. M e a n n u m b e r s o f A m b l y s e i u s victoriensis p e r 100 leaves o n Ellendale m a n d a r i n s in t w o o r c h a r d s , o n e in w h i c h t h e R h o d e s grass g r o w i n g in t h e i n t e r - r o w s was m o w e d at 7 - 1 0 " - d a y intervals a n d t h e o t h e r in w h i c h it was i n f r e q u e n t l y m o w e d at 3 - m o n t h l y intervals, 1 9 8 6 - 8 7 .
210
D, SMITH AND D.F. PAPACEK
100
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80
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~ 40 d
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Fig. 11. Percentage o f fruit infested with Tegolophus australis and n u m b e r s ofAmblyseius victoriensis per 100 leaves of Ellendale m a n d a r i n s in 1987-88, following an a u g m e n t a t i v e release ofA. victoriensis on 18 D e c e m b e r 1987.
T. australis. By 1989-90 in this orchard, T. australis appeared to be much more tolerant of the available miticides fenbutatin oxide, dicofol and sulphur. Foliar applications o f micronutrients Zn, Mb, Mg, Mn, B and KNO3, and o f ethrel had no effect on A. victoriensis.
STUDIES OF AMBLYSEIUS: CONTROL OF TEGOLOPHUS AND PHYLLOCOPTRUTA
213
Use of alternative host plants Mean numbers ofA. victoriensis in Ellendale mandarin orchards with frequent and infrequent mowing of inter-rows are given in Fig. 8. Numbers of A. victoriensis were slow to build up in the frequently mowed orchards and did not reach 40 per 100 leaves until late in the season. In contrast, predator numbers in the infrequently mowed orchards exceeded 40 per 100 leaves by the end of December. Amblyseius victoriensis numbers on Imperial mandarins adjacent to and distant from a E. torelliana windbreak are given in Fig. 9. Amblyseius victoriensis was not recorded in the distant block of mandarins until 3 March by which date, numbers in the adjacent block were 38 per 100 leaves. Tegolophus australis infestations remained very low in the citrus blocks represented in Figs. 8 and 9.
Augmentative releases Mean numbers of A. victoriensis on Ortanique mandarins in release and non-release trees are given in Fig. 10. Amblyseius victoriensis was detected at the first assessment on 1 January in the release trees and there were 14 per 100 leaves by 22 January. The predator was first detected a week later on adjacent trees, but numbers were not comparable to those on release trees until 19 February. A T. australis infestation did not develop in the block following a spray of fenbutatin oxide in m i d November. The percentage of fruit infested with T. australis, and A. victoriensis numbers in a block of Ellendale mandarins into which A. victoriensis were released on 18 December, are given in Fig. 11. The predator was first detected on 8 Jranuary and numbers exceeded 40 per 100 leaves by 6 April. The T. australis infestation which had begun to increase on 28 December declined to zero on 5 February.
DISCUSSION
Efficacy Amblyseius victoriensis was a very c o m m o n predator on citrus in the Gayndah-Mundubbera area during the six seasons. It was active in 64.7-92% of the blocks (Table 1 ), and was absent usually only where heavy suppression by pesticides occurred (Table 3 ). The majority of blocks in the efficacy study had a resident A. victoriensis population of 10-20 per 100 leaves by November (Figs. 1 and 3 ).
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D. SMITH AND D.F. PAPACEK
Amblyseius victoriensis overwinters successfully on citrus in south-east Queensland, feeding on remnant rust mite populations, tydeids, tenuipalpids, tarsonemids and wind-blown pollen (James, 1989a). James (1989b) noted that A. victoriensis in southern New South Wales overwinters as non-reproductive females on evergreen vegetation or weeds, feeding on tydeid or tenuipalpid mites. Movement into peach orchards does not occur until January. Strong populations of A. victoriensis continued in the citrus even after the host T. australis had been reduced to zero levels (Fig. 2 ). Populations in late spring tended to be low if disruptive scalicides like methidathion had been applied in the winter or early spring. This caused problems, particularly with P. oleivora, in late spring to early summer. Amblyseius victoriensis populations of 10-20 per 100 leaves rapidly increased to 100 or more and contained or rapidly controlled T. australis. Amblyseius victoriensis was able to contain light P. oleivora infestations (5% or less fruit infested) if numbers of predators were 40 or more per 100 leaves throughout the season. Once P. oleivora fruit infestation rose to 10% or higher, it was usually necessary to apply a miticide. Also ifA. victoriensis fell for any reason during the season, P. oleivora tended to increase quickly. Amblyseius victoriensis was observed feeding in the laboratory on all stages of T. austral& but only on eggs and quiescent stages ofP. oleivora; this probably explains the differences in efficacy. Tegolophus australis occurred in 54.3-89.1% of the blocks. Phyllocoptruta oleivora occurred in 74.1, 76.1 and 36.8% of the blocks in the first three seasons but then dropped to 5.7, 0.3 and 0.3% in the last three seasons. Table 4 shows rainfall, number of wet days and the number of days with temperatures above 35~ Temperatures above 35~ coupled with dry weather are detrimental to P. oleivora (Smith, 1972). While correlation between P. oleivora incidence and weather was not strong, the first six months of 1987-88,1988-
TABLE 4 Rainfall, number of wet days and number of days with temperatures (T) above 35 ~C, 1984-90, recorded at Brian Pastures Research Station, Gayndah Year
1984-85 1985-86 1986-87 1987-88 1988-89 1989-90
Total rainfall ( m m )
No. wet days
Sept.-Aug.
Sept.-Feb.
Sept.-Aug.
Sept.-Feb.
Days with T>35~ Sept.-Aug.
700.4 859.0 664.2 677.6 689.2 679.4
422.2 632.6 477.2 307.2 379.8 316.6
91 90 91 92 101 79
49 57 50 39 47 36
28 10 19 30 17 31
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215
89 and 1989-90 tended to be drier than in the earlier years and 1987-88 and 1989-90 were the hottest. Mancozeb (and mezineb) normally used for disease control also control P. oleivora, but are much less effective against T. australis. However, there was no clear correlation between mancozeb use and P. oleivora incidence (Table 1 ).
Lffect of pesticides The use of mancozeb (and mezineb) is very detrimental to A. victoriensis and commits the grower to miticidal control for the season. Both materials are effective for controlling the disease black spot, Guignardia citricarpa, and are applied six and twelve weeks after petal fall. Goodwin (1984) reported mancozeb to have a low toxicity to Phytoseiulus persimilus Athias Henriot. Copper oxychloride fulfils the same disease-control function as mancozeb, and is non-toxic to A. victoriensis; however, some growers prefer to limit its use to avoid darkening of wind blemish. The results for most of the other pesticides agree with those of Jeppson et al. (1975 ) on four Californian species and Watve and Lienk ( 1975 ) on Amblyseiusfallacis ( G a r m a n ) and Typhlodromus pyri Scheuten. The decrease in toxicity over the six seasons for some of the pesticides, viz. chlorpyrifos, fenbutatin oxide and endosulfan, is encouraging as to the development of resistance in A. victoriensis. The develo p m e n t of resistance to pesticides in phytoseiids has been known for nearly 40 years (Huffaker and Kennett, 1953 ), and offers more scope for integrating chemical and biological controls.
Use of alternative host plants Orchards where the inter-row cover of Rhodes grass was allowed to flower and pollinate consistently had larger populations of A. victoriensis than orchards mowed every 7-10 days. Rhodes grass is a South African perennial tufted species with erect flowering stems and spreading surface runners. It is primarily a summer-growing species, and a c o m m o n pasture and orchard grass in areas such as Gayndah and Mundubbera, where the annual rainfall is about 750 ram. It flowers continually from October to about April, producing a fine yeUow pollen which blows onto the citrus. Laboratory studies have shown that A. victoriensis feeds and reproduces on this pollen. The results suggest that inter-row flowering of Rhodes grass should be encouraged, particularly in orchards where rust mites are troublesome. Many Gayndah and Mundubbera orchardists now do this. At c o m m e n c e m e n t of this study, inter-row mowing practice amongst growers varied from weekly to every three weeks to every three months. Many growers now m o w alternate inter-rows every three
216
D. SMITH AND D.F. PAPACEK
weeks, allowing sufficient time for the Rhodes grass to pollinate while maintaining neat orchards. Kennett et al. (1979) discussed the benefit of windborne pollens as a supplementary food for Amblyseius hibisci (Chant) in citrus in California. Encouragement of the perennialAgeratum conyzoides L. for its pollen is recommended to promote control of Panonychus cirri (McGregor) by Amblyseius newsami (Evans) in citrus in Guangdong Province, China (Huang, 1978). Eucalyptus torelliana is a common host of A. victoriensis in the Gayndah and Mundubbera area, often carrying populations of several mites per leaf. Tydeids occur on the foliage but often there is little evidence of any host mites as a food source. The undefleaf surface of E. torelliana is quite hairy and the hairs are popular oviposition sites for A. victoriensis and also possibly act as a trap for wind-blown pollen. Avocado foliage is another favourite site for A. victoriensis, often again with little evidence of host mites as a food source. Amblyseius victoriensis is reported to feed on a range of foods m natural sugars such as honeydew and plant exudates, a wide range of pollens from native trees and introduced ornamentals, several species of eriophyid mites, tydeid mites, tenuipalpid mites, two-spotted mite Tetranychus urticae Koch, scale insect crawlers and immature thrips (James, 1989a). A nearby windbreak row of E. torelliana acting as a reservoir of windblown A. victoriensis in this study resulted in quicker re-establishment in citrus following application of a disruptive pesticide. Hoy et al. (1985 ) showed that phytoseiids use air currents as a major means of dispersal. James ( 1989b ) concluded that provision of evergreen overwintering refuges for A. victoriensis would enhance colonization of peach orchards in the spring in southern New South Wales. Eucalyptus torelliana is a popular tree used for windbreaks in south-east Queensland, and the results suggest that they can act as a natural reservoir for A. victoriensis populations. At least one recently established orchard at Mundubbera has been designed with E. torelliana windbreaks around each block, and enjoys consistently high numbers ofA. victoriensis.
Augmentative releases Both augmentative releases established A. victoriensis and prevented subsequent development of T. australis infestations. The releases promoted predator activity by four to six weeks. The practice of releasing would be much enhanced ifA. victoriensis could be successfully mass-reared. This has not yet been achieved mainly because the predator is difficult to keep contained within a rearing arena (McMurtry and Scriven, 1965 ). The collection of E. torelliana, avocado or citrus leaves for transferring A. victoriensis is being increasingly practised by orchardists, but is time-consuming.
STUDIESOFAMBLYSEIUS:CONTROLOF TEGOLOPHUSANDPHYLLOCOPTRUTA
217
REFERENCES Broadley, R.H., Smith, D., Papacek, D.F., Owen-Turner, J.C., Chapman, J.C., Banks, A.G. and Mayers, P., 1987. Protect your citrus. Qld. Dep. Primary Ind. Inf. Set., Q 187012:141 pp. Goodwin, S., 1984. Biological control of Acari: Laboratory evaluation of pesticides on an Australian strain of the Chilean predatory mite, Phytoseiulus persimilis Athias-Henriot. In: D.A. Griffiths and C.E. Bowman (Editors), Acarology VI, Vol. 2. Ellis Horwood, Chichester, pp. 647-654. Hoy, M.A., Groot, R. and Van de Baan, H.E., 1985. Influence of aerial dispersal on persistence and spread of pesticide resistant Metaseiulus occidentalis in California almond orchards. Entomol. Exp. Appl., 37: 17-31. Huang Ming-dau, 1978. Studies on the integrated control of the citrus red mite with the predaceous mite as a principal controlling agent. Acta Entomol. Sinica, 2 l: 260-270 (in Chinese, with English abstract). Huffaker, C.B. and Kennett, C.E., 1953. Differential tolerance to parathion in two Typhlodromus predators on cyclamen mite. J. Econ. Entomol., 46: 707-708. James, D.J., 1989a. Influence of diet on development, survival and oviposition in an Australian phytoseiid, Amblyseius victoriensis (Acari: Phytoseiidae). Exp. Appl. Acarol., 6: 1-10. James, D.J., 1989b. Overwintering ofAmblyseius victoriensis (Womersley) (Acarina: Phytoseiidae) in southern New South Wales. Gen. Appl. Entomol., 21:51-55. Jeppson, L.R., McMurtry, J.A., Mead, D.W., Jesser, M.J. and Johnson, H.G., 1975. Toxicity of citrus pesticides to some predacious phytoseiid mites. J. Econ. Entomol., 68:707-710. Kennett, C.E., Flaherty, D.L. and Hoffman, R.W., 1979. Effect of wind-borne pollens on the population dynamics ofAmblyseius hibisei (Acarina: Phytoseiidae). Entomophaga, 24: 8398. McMurty, J.A. and Scriven, G., 1965. Insectary production of phytoseiid mites. J. Econ. Entomol., 58: 282-284. Overmeer, W.P.J., Doodeman, M. and Van Zon, A.Q., 1982. Copulation and egg production in Amblyseius potentillae and Typhlodromus pyri (Acarina: Phytoseiidae). Z. Angew. Entomol., 93:1-11. Schicha, E., 1987o Phytoseiidae of Australia and Neighbouring Areas. Indira Publishing, Oak Park, Michigan, 187 pp. Smith, D., 1972. Queensland Department of Primary Industries, Entomology Annual Report for 1972 Nambour. Smith, D. and Papacek, D.F., 1984. Integrated control of Aonidiella aumntii (Maskell) and other citrus pests at Mundubbera, Queensland. Qld. Dep. Primary Ind. Bull., Series QB84002: 16 pp. Smith, D. and Papacek, D.F., 1985. Integrated pest management in Queensland citrus. Qld. Agric. J., 111: 249-259. Watve, C.M. and Lienk, S.E., 1975. Responses of two phytoseiid mites to pesticides used in New York apple orchards. Environ. Entomol., 4: 797-800.
