Insect Sci. Applic. Vol. 19, No. 2/3, pp. 173-178, 1999 Printed in Kenya. All rights reserved
0191-9040/99 $3.00 + 0.00 ©1999 ICIPE
MANAGEMENT OF THE WHITEFLY BEMISIA TABACI (GENN.) ON MELON BY VACUUM REMOVAL PHYLLIS G. WEINTRAUB AND A. RAMI HOROWITZ
Department of Entomology, ARO, Gilat Experiment Station, D.N. Negev, 85280, Israel
{Accepted 30 August 1999)
Abstract—The efficacy of a field vacuum unit for the management of Bemisia tabaci was evaluated on melon (Cuciimis nwlo L.) during two summer seasons. The tractor-mounted unit was designed to dislodge insects by blowing air from lateral vents onto the plants while simultaneously vacuuming from above. Field observations, collection of leaf samples, and hand-vacuum sampling before and after the field vacuuming were used to evaluate the efficacy of removal. Bemisia tabaci population reductions were significant (30-60%) and lasted from week to week when vacuumed weekly. Parasitoid populations were slightly affected, but were not significantly different from populations in the untreated control plot. Field vacuuming was found to be as effective as insecticide applications for the control of B. tabaci in melons. Key Words: insect management, vacuuming, Bemisia tabaci Resume—Des essais ont ete realises en champ durant deux ans afin d'evaluer l'efficacite d'un appareil a succion en vue de la lutte contre B. tabaci (Genn.). L'unite a ete conc,ue pour deloger des insectes en soufflant de l'air sur des plants de fagon laterale et, simultanement en aspirant les insectes par une bouche situee au-dessus. On a utilise des observations au champs, la collecte d'echantillons de feuilles et l'aspiration manuelle pour evaluer l'efficacite. Des reductions significatives (30-60%) de populations ont ete observees et elles duraient une semaine. Les populations de parasitoi'des ont ete legerement affectees, mais les populations n'etaient pas significativement differentes de celles estimees dans les parcelles temoins. En parcelle de melons, l'aspiration a donne un niveau de controle egal aux applications insecticides. Mots Cles: regie des insectes, aspiration, Bemisia tabaci INTRODUCTION
which, for various reasons (adverse ecological/ environmental effects, resistance to insecticides, or product non-availability), can be controlled by increasingly fewer pesticides. Vacuum units have been shown to reduce populations of Lygus spp. in strawberries (Vincent and Lachance, 1993; Pickel et al., 1994) with varying levels of success. For example, Boiteau et al. (1992) evaluated the efficacy of vacuuming the Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say), and found that adults and large larvae were easily removed from potato plants. During the course of their investigations, they found that large numbers of aphids were also removed by the vacuuming. Weintraub et al. (1996) demonstrated population
V
acuum removal is an innovative alternative to chemical control of insect pests. It bypasses problems associated with insect resistance to pesticides, and has the additional advantage of enhancing pollen dispersal in crops such as strawberries (Chiasson et al., 1995). The historical development of vacuum units for insect control has been reviewed elsewhere (Weintraub et al., 1996). The insects of primary focus for this kind of control are those that are easily dislodged, and Corresponding author: PGW. E-mail:
[email protected]
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reductions of 50-75% for Bemisia tabaci (Genn.), leafhoppers and aphids in celery and potato. They demonstrated that sustained population reductions were achieved when experimental plots were large; small plots (12 x 15 m) were easily reinvaded due to their large perimeter relative to the area. We present the results of vacuuming melon (Ciicumis melo L.) crops in semi-commercial fields, during two seasons, for the control of B. tabaci, and discuss the impact of this method on whitefly natural enemies. MATERIALS AND METHODS Vacuum unit The tractor-mounted vacuum unit is unique in that it incorporates two perpendicular blowers directed on either side of a standard 1.9-m-wide bed of plants to dislodge insects. A vacuum, located above and encompassing the entire area between the blowers, immediately removes insects thus dislodged (see Weintraub et al., 1996). Air is blown onto the plants and vacuumed upwards at an air speed of 40 m/sec. The vacuum unit can be raised or lowered either by physically raising or lowering the unit within the frame or by changing the wheel size, to avoid plant damage and enhance efficiency of insect removal. The unit can be completely raised above the plants once the end of a row is reached, or as needed. The tractor moves through the fields at a speed of about 4 km/h. In our experiment a 1.5-m-long canopy frame was welded to the front of the unit and heavy canvas secured to the frame, draping to the ground, thus reducing the possibility of insects flying out of the path of the vacuum unit. Insecticides/Fungicides The following insecticides were used: abamectin (Vertimec, 18 g/1 [emulsifiable concentrate] Merck Sharp & Dohme, distributed by S. Riesel, Ltd., Ramat Gan, Israel); acetamiprid (Mospilan, 200 g/ 1 [soluble powder] Nippon Soda Co., Ltd., distributed by Agan Chemical Manufacturers, Ltd., Ashdod, Israel); and diafenthiuron (Pegasus, 250 g/1 [soluble concentrate] Novartis, distributed by Milchan Bros Ltd., Ramat Gan, Israel). The following fungicides were used: mancozeb (Manzidan, 80% [wettable powder] Rohm and Haas Co., distributed by Makhteshim Chemical Works, Ltd., Be'er Sheva, Israel) and quinoxyfen
(Avir, 250 g/1 [soluble concentrate] DowElanco, distributed by Agrichem Ltd., Petach Tikva, Israel). A tractor-driven spray unit was used for application of all insecticides and fungicides. 1996 trial The trial was carried out at Kibbutz Erez (34°34' E longitude, 31°34' N latitude) in the western Negev region of Israel. Eighteen 80-m-long beds were planted with variety B-8 melon seedlings (Citcumis melo L.) on 16 June 1996, and irrigated by drip lines. All plots were treated weekly with mancozeb (2 kg/ha) to prevent downy mildew. The vacuum plot was 9 beds wide by 80 m long, while untreated control and insecticide-treated plots were 9 beds wide by 40 m long. The field was vacuumed once a week, commencing at approximately 0800 h. Insecticides were applied as follows to the insecticide-treated plot only: diafenthiuron (375 g/ha) on 12 and 19 July and acetamiprid (0.15%) on 2 August. All plots were treated with abamectin (500 g/ha) mixed with 1% Ultrafine® oil on 26 July to control a severe spider mite (Tetranychus cinnabarinus (Boisduval)) infestation. To prevent physical damage to the vines by the tractor wheels, vines were once moved out of the furrows and onto the beds. Thereafter, the blowing action of the vacuum unit prevented them from growing back into the furrows. Melons were harvested from two 5-mlong replicates within each treatment plot on 23 and 27 September. 1998 trial The trial was also carried out at Kibbutz Erez. Eighteen 125-m-long beds were planted with 'Ofer' melon seedlings on 23 June 1996 and irrigated by drip lines. As in the 1996 trial, all plots were treated weekly with mancozeb (2 kg/ha) to prevent downy mildew and once with quinoxyfen (400 g/ha) to guard against powdery mildew on 11 August. The vacuum plot was 8 beds wide by 125 m long, while untreated control and insecticide-treated plots were 10 beds wide by 62 m long. The field was vacuumed once a week, commencing at approximately 0800 hours. Acetamiprid (0.15%) was applied to the insecticide-treated plot only on 15 and 30 July, and 13 August. The control plot was untreated. As in the previous trial, vines were once moved out of the furrows onto the beds to prevent physical damage to the vines by the tractor wheels. Melons
Whitefly management by vacuum insect removal were harvested from five 5-m-long replicates within each treatment plot on 8 and 15 September.
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RESULTS
Field vacuuming proceeded according to schedule, unimpeded by weather conditions or other factors. Bemisia tabaci population densities differed between the two years that the trials were An Echo®, model no. PB 1000 leaf blower was performed. The average B. tabaci population size, converted to a hand-vacuum unit by switching as determined by the hand-vacuum sampling, was the air intake and exhaust ports. A 1.5 m hose was significantly larger in 1996 as compared with 1998 fitted to the intake port. Bags of fine mesh nylon (F = 248.4, df = 1, P < 0.001). In spite of these were made to fit the 11 cm diameter opening to population differences, there were still significant the hose and were secured with rubber bands. The differences between the treatments for both years air speed of this vacuum was 60 m/s. Before the 63.5, df=2,P< 0.001). On average, vacuum(F = field was vacuumed, five 1-m bed-wide samples treated plots had significantly lower B. tabaci (a bed is 1.9 m wide) were taken from all plots by populations than insecticide-treated plots, which passing the hand-vacuum back and forth over the in turn had significantly lower populations than entire width of the row for 10 seconds. the untreated control plots (Fig. 1). Immediately after field vacuuming was finished, Although 1996 data on the density of B. tabaci an additional 5 samples were taken from the immatures on random leaves were collected only vacuumed plot. Bags were placed in a freezer until for the last three weeks of the season, results the contents could be assessed. The numbers of similar to those described above were obtained; B. tabaci adults and of two whitefly parasitoids vacuum-treated plots had significantly fewer {Eretmocerus mimdiis Mercet and Encarsia hitea immatures than untreated control or insecticide(Masi)) were counted. treated plots (Table 1). From the 2-way ANOVA Leaves (30 in 1996 and 50 in 1998) were (year and treatment were independent variables), randomly collected from each plot and taken to there were significant differences (F = 202.0, df = the laboratory for immediate evaluation. Third 1, P < 0.001) in the average density of immature instar and pupal B. tabaci were counted. Three B. tabaci on leaves between 1996 and 1998. The samples (one per week) were taken at the end of vacuum-treated plots had significantly (F = 56.9, the 1996 season and weekly samples were taken df = 2, P < 0.001) fewer immature B. tabaci than during the 1998 season. both the untreated control plots and the insecticide-treated plots. Data analysis There were significantly more whitefly parasitoids counted in hand-vacuum samples in Samples were taken in a completely random 1996 than in 1998 during the final three weeks of manner and each sample constituted a replicate the trials (F = 26.4, df = 1, P < 0.001). However, on its own. Although the trials were not initiated there were no significant differences in the number on the same date of each year of the experiment, of parasitoids found in the three treatments (F = they were carried out for the same length of time. 0.5, df=2,P = 0.64) (Table 3). Insect population data, obtained by counting the Adult Bemisia tabaci numbers in vacuum samples and on leaves, were analysed initially in a 2-way analysis of variance On all occasions, the density of B. tabaci in the (ANOVA) with treatments and year as vacuum plot was lower after the field vacuum independent variables. Results from each year treatment (Fig. 1). In 1996, the average density of were analysed separately by 1-way ANOVA. B. tabaci in the vacuum-treated plot was Means were separated by the Tukey or Tukeysignificantly less than that of the untreated control Kramer multiple range test (Zar, 1996). Harvest and insecticide-treated plots (F = 13.2, df = 2, P < data were first arranged in a 2 x 3 contingency 0.001). There were no significant differences table, then a 2 x 2 contingency table, and analysed by %2. All analyses were conducted at the 0.05 level between the B. tabaci populations in the untreated control and insecticide-treated plots. In 1998, B. of significance. tabaci populations in the vacuum-treated plot remained significantly lower than those in the untreated control but insignificantly different Sampling
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P. G. WEINTRAUB and A. R. HOROWITZ IV I ^M —•— --o--
4/7
7/7
21/7
28/7
Before After Control Insecticide
15/7
11/8 Sampling date
Fig. 1. Efficacy of field vacuuming on populations of adult Beinisia tabaci in 1996 and 1998 as evidenced by handvacuum sampling. 'Before' and 'After' refer to samples taken in the vacuum-treated plot immediately before and immediately after the field was treated respectively. Hand-vacuum samples were taken from the untreated control and insecticide-treated plots while the vacuum-plot was being treated. Bars and dots denote means and vertical lines denote standard error
from the insecticide-treated plot until near the end of the trial (F = 10.1, df=2,P = 0.001). Table 1. Mean number (+ SE) of live 3rd instar and pupal B. tabaci per leaf (30 leaves per treatment-date) at end of 1996 season Sampling date Treatment 4 August 5 August 12 August Vacuum 44.4 ± 6.2 A 32.4 ± 4.7 A 4.5 ±0.8 A Insecticide 193.4 ± 18.1 B 129.1 ±15.3 B 13.5 ±2.2 B Control 212.1 ± 27.0 B 105.3±12.9 B 13.9±2.0 B Different letters within the same column indicate significant difference (P < 0.001).
Immature Beinisia tabaci Towards the end of the 1996 trial, leaf samples were collected to determine the effect of the reduced adult population on densities of immature stages. Table 1 shows that the number of live 3rd instars and pupae found in the vacuumtreatment was significantly lower (F = 25.6, df= 1, P < 0.001) than that of the untreated control or insecticide-treated plots. In the 1998 trial, the average density of 3rd instars and pupae counted on leaves from the vacuum-treated plots was significantly less (F = 50.1, df=2,P< 0.001) than that in the untreated control but, not significantly
Whitefly management by vacuum insect removal
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Table 2. Mean number (+ SE) of live 3rd instar and pupal B. tabaci per leaf (50 leaves per treatment-date) during the 1998 season Sampling date Treatment 14/7 20/7 3/8 10/8 17/8 27/7 Vacuum 0 0 8.9 ± 2.4 A 38.3 ±5.7B 24.3 ±4.7 A 13.0 ±2.1 A Insecticide 0 9.1 ±1.7 A 0 3.0 +2.0 A 14.5 + 2.3 A 12.9 ±2.3 A 0 Control 0 12.1 ±3.5 A 63.5 ±5.5C 45.7 + 7.1 B 37.0 ± 6.0 B Different letters within the same column indicate significant difference (P > 0.001).
24/8 4.2±0.9A 11.1 ±3.4 A 35.0 ± 6.2 B
31/8 2.5±0.7A 3.7+1.1 A 11.4±2.3B
Table 3. Average number (± SE) of whitefly parasitoids (Eretmocerus miiridus Mercet and Encarsia lutea (Masi)) as determined by hand-vacuum sampling, during the 1998 season Sampling date 20/7 24/8 Field treatment 14/7 27/7 17/8 3/8 10/8 8.4 ±2.2 1.8 ±0.9 Vacuum before 1.8 ±0.8 0.4 ±0.2 4.2 ±1.3 19.8 ±2.6 20.6 ± 2.9 1.2 ±0.7 Vacuum after 0.4 ±0.4 0.4 + 0.2 3.8 ±1.0 3.4 ±1.2 6.2 ±1.7 16.8 ± 1.7 7.6 ±4.0 Insecticide 7.4 ±1.3 0.6 ±0.2 0.6 ±0.4 3.0 ±0.9 18.2 ±2.7 13.4 ± 3.7 3.0 ±1.8 Control 3.4 ±0.9 0.4 ±0.2 1.6 ±0.5 28.0 ±4.5 31.0 ±11.8 11.6 ±1.8 There were no significant differences (P < 0.001) between the treatments within the same column.
different from the insecticide-treated plot (Table 2). Parasitoids The number of whitefly parasitoids (Er. mundus and En. lutea) was reduced immediately after field vacuuming; however, there were no significant differences (F = 3.6, df= 2,P = 0.058) in the number of parasitoids in the three treatment plots (Table 3).
31/8 ± 0.6 ± 0.4 ± 0.4 ± 0.5
2 .2 0 .8 2 .8 2 .2
Table 4. Melon yields ' 1998 1996 Avg. Wt (kg) No. No. Treatment Vacuum 62 A 50 A 1.22 A 52 A 1.11 A 45 B Insecticide 48 B 52 A 1.16A Control Different letters within the same column indicate significant differences (P < 0.05).
densities were not significantly lower than the population in the untreated control plots. The results presented herein support the previously Yield reported findings for control of B. tabaci in celery and potatoes (Weintraub et al., 1996) using this In 1996 plants in the vacuum-treated plot showed same vacuum unit. fewer signs of viral infection (leaf yellowing and We were concerned about there occurring curling) than the insecticide-treated or untreated direct physical damage to the crop as a result of control plots and produced significantly more melons at harvest {%2 = 3.6, df= 2,P< 0.05); (Table the passage of the tractor and the blowing/ vacuuming actions. Nevertheless, not only were 4). In 1998, there was less evidence of differences the plants not damaged by the vacuum treatment, in viral infection in the plots, and there were no in one trial the treated plants had larger yield than significant differences in the average number of untreated control or insecticide-treated plants. melons or their average weight per treatment plot During the 1996 trials, the plants in the (Table 4). insecticide-treated plot exhibited signs of viral infection similar to the untreated control plot, DISCUSSION indicating unsuccessful B. tabaci control. Melon yield in the vacuum-treated plot was higher than These trials have shown that weekly field in either the insecticide-treated or untreated vacuuming with our uniquely designed vacuum unit can control B. tabaci in melons as effectively control plot, indicating that field vacuuming once a week was sufficient to control B. tabaci as 2-3 insecticide applications. Furthermore, it populations effectively. Less viral infection was was shown that while parasitoid populations were seen in 1998, indicating that application of slightly reduced by the field vacuuming, their
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acetamiprid might have been more effective in controlling B. tabaci than diafenthiuron. Field vacuuming was as fully efficacious as the insecticide treatment since there were no significant differences in adult populations or yield. The machine used in this research is a prototype, treating one bed at a time; therefore, direct cost analysis was not possible. However, that this type of control is economical is evidenced by the fact that there are large commercial strawberry growers in California, USA, who are using vacuum machines, sometimes in conjunction with the judicious use of insecticides, for the control of Lygns spp. (Street, 1989; Moore, 1990). Furthermore in strawberries, there is the added benefit of pollen dispersal. Commercial machines treat' six to eight beds at a time; treatment requires about the same amount of time as is required to apply insecticides to a field. This study demonstrates that this form of mechanical control could be the sole means of insect control. Realistically, we can foresee its use in insect pest management programmes; field vacuuming is fully compatible with chemical control measures, reducing pest populations either by replacing a regular pesticide application or immediately before it. Furthermore, the efficacy of biological control agents may be greatly improved by first reducing insect pest populations by field vacuuming immediately before their release. Acknowledgements—The authors acknowledge contributions from Yossi Arazi, Moshe Laniado,
Sophia Kleitman for assistance with the trials; Ruth Marcus for assistance with the statistical analysis; Janis Joseph for editorial comments, and the Chief Scientists of Ministries of Agriculture and of Arts and Sciences, Jerusalem, Israel for financial support. This paper is contribution No. 538, 1998 series, from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. REFERENCES Boiteau G., Misener G. C, Singh R. P. and Bernard G. (1992) Evaluation of a vacuum collector for insect pest control in potato. Am. Potato /. 69,157-166. Chiasson H., de Oliveira D. and Vincent C. (1995) Effects of an insect vacuum device on strawberry pollination. Can. }. Plant Sci. 75, 917-921. Moore J. (1990) Sweeping fields controls some pests. Am. Veg. Grower March 3,10-11. Pickel C, Zalom F. G., Walsh D. B. and Welch N. C. (1994) Efficacy of vacuum machines for Lygus hesperus (Hemiptera: Miridae) control in coastal California strawberries. /. Econ. Entomol. 87,16361640. Street R. S. (1989) The bug sucker. Agrichem. Age March: 3, 38-39. Vincent C. and Lachance P. (1993) Evaluation of a tractor-propelled vacuum device for management of tarnished plant bug (Heteroptera: Miridae) populations in strawberry plantations. Environ. Entomol. 22,1103-1107. Weintraub P. G., Arazi Y. and Horowitz A. R. (1996) Management of insect pests in celery and potato crops by pneumatic removal. Crop Protection 15, 763-769. Zar J.H. (1996) Biostatistical Analysis, 3rd ed. PrenticeHall, Englewood Cliffs, NJ. 620 pp.
