Dispersal of Bemisia tabaci the Sweet Potato Whitefly, & Members of its Parasitoid Complex David N. Byrne, Jacquelyn L. Blackmer#, David Bellamy, David Donnell, Rufus Isaacs and Klaas H. Veenstra Dept. of Entomology, University of Arizona, Tucson, AZ 85721 USA #CCTA/UENF, Brazil Dept. of Entomology, 203 Pesticide Research Center, Michigan State University, East Lansing, MI 48824 USA. Abstract* This report focuses on the progress made during the last year in our laboratory's examination of short (<5.0 km) range migration of the sweet potato whitefly, Bemisia tabaci (Gennadius). We also report preliminary results of experiments concerning the whitefly parasitoid Eretmocerus eremicus. We are also investigating the vertical components of whitefly dispersal in the field. Preliminary results show the intense concentration of the flying population near to the ground. Also, marked whiteflies were routinely caught in the highest traps (7.2 m) on a series of trestles. This was true even in the trestles placed at the field edge. This indicates that a portion of the population dispersing from a field immediately rises to reasonably high altitudes. More recent work with traps suspended from balloons has shown that whiteflies can be captured at heights of at least 150' during early morning hours. Sex ratios and potential weights were similar regardless of the heights at which the whiteflies were captured. In a vertical flight chamber we found that E. eremicus, unlike B. tabaci., flew multiple times. Individuals as old as 21 days flew in the chamber. Additionally, females flew for considerably longer periods of time than did males. There was some response to a visual light cue (plant simulator), but not at the level seen previously with whiteflies. Introduction On a worldwide basis Bemisia tabaci (Gennadius), the sweet potato whitefly, continues to be one of the principle pests of crops grown for food and fiber. Because there are no viable alternatives to chemical control available (i.e., resistant varieties or profitable alternative crops), growers are left with one principle control strategy; the application of pesticides. It recent years there has been almost total reliance on the class of chemicals known as the chlornicotinyls. This is not environmentally sound nor does it insure long-term success. High levels of insecticides resistance has already been reported in parts of Europe and seem to exist the Southwest as well. We feel that a better understanding of whitefly dispersal behavior will lead to management strategies that are less pesticide dependent. Additionally, our laboratory has recently been working to character the flight behavior of the whitefly parasitoid Eretmocerus. It seems that if individuals involved in biological control efforts are going to tout the use of refugia as a means of managing whitefly numbers then information concerning flight by these wasps would seem important. During the last nine years, various members of our laboratory have examined what we term mid-range dispersal (by our definition on the scale of a few kilometers). The focus in this report is to discuss the progress made this last year concerning our understanding of short (< 1.0 km) and long-range (>5.0 km) dispersal by B. tabaci., in a large part by testing our hypotheses in the field. Laboratory Experiments in 1996-7 Behavioral aspects We examined the response by B. tabaci that had dispersed from agricultural fields (primarily melons) to visual stimuli. Whiteflies were, in general, strongly attracted to yellow placards, but displayed no response to single mature cotton plants that were presented as targets. Their response to yellow did not seem to be dependent upon distance traveled (from 0.7 to 2.1 km). The increase in numbers caught in traps with a yellow placard was negatively correlated with wind speed (from 1.0 to 5.0 m/s), but not with solar radiation or temperature. Dispersal in B. tabaci is apparently not entirely passive, but the ability to respond to vegetative stimuli likely decreases as wind speed increases. Evidence indicates that prevailing winds can interfere with the ability of B. tabaci to alight on potential hosts. Physiological aspects We examined the reproductive physiology of B. tabaci after their dispersal from cotton fields. In particular, we were interested in the synthesis of vitellogenins and the production of mature eggs. Whiteflies that dispersed out of fields, and were flying approximately 0.1 m above the soil surface, exhibited a reproductive physiology that was not significantly different from that exhibited by whiteflies that remained in cotton fields. B. tabaci captured in fan traps placed at 2.1 m matured eggs at a significantly lower rate. It appears that these latter whiteflies exhibit a physiology that indicates a reallocation of nutrients and energy resources in support of dispersal. We have attempted to measure similar traits in whiteflies caught at heights of 50, 100 and 150 m. This work is yet to be completed. We have found significant differences in sex ratios and weights that varied with height. Parasitoid flight behavior The dispersal abilities of the parasitoid Eretmocerus eremicus (Hymenoptera: Aphelinidae) were examined in a vertical flight chamber to determine its dispersal potential and to compare this to the flight behavior of B. tabaci (Hemiptera: Aleyrodidae). Individual wasps of known age and sex were placed on a raised platform in a vertical flight chamber (31" x 32" x 35") illuminated by a sodium-vapor light from above. Wasps were given two minutes to respond to the light by taking flight. Once airborne, timing of the flight began and a regulated air current was induced to model a vertical climb. Wasps were exposed to a ten second vegetative cue every sixty seconds while in flight to test their migratory state. Flight sessions ended when the wasps ceased flying for a period longer than two minutes. Preliminary results clearly indicate that there is a statistical difference in observed flight times in a vertical flight chamber between males (1 min. avg., 10 min. longest flight) and females (19 min. avg., 93 min. longest flight). Initial results also suggest that there exist two distinct populations within females of short-duration flyers (<20 min.) and long-duration flyers (>25 min.). Field Experiments 1996-7 The aerial distribution of B. tabaci during the early ascent phase of flight was studied over two summers in southwestern Arizona, to test the possibility of making predictions about dispersal patterns from our understanding of flight behaviors. Marked whiteflies were trapped at four heights between 0 and 7.27 m above fallow ground, and at six distances between 0 to 100 m from the insect source. Insects were trapped during a 2-3 h period after the initiation of flight activity during parts of 1995 and 1996. Analysis of the trap catch data revealed a clear negative exponential relationship between height and aerial distribution, and a slightly weaker negative power relationship between distance and aerial distribution. Marked insects were caught in the uppermost traps adjacent to the source, indicating that a portion of the population has a strong capacity for ascent out of the flight boundary layer. Egg-load decreased with the height, but not the distance, at which B. tabaci was trapped. Mean egg load close to the ground was significantly greater than that for those trapped at 4.8 and 7.2 m, supporting the hypothesis that there is a trade-off between flight and oogenesis in weak-flying insects. Air temperatures during the trapping periods were positively correlated with the proportion of male and female B. tabaci caught in the highest traps, but not in the most distant traps. The significance of these results for accurate prediction of whitefly dispersal is discussed, and the importance of individuals behavior in determining dispersal patterns of small insects is emphasized. We also examined vertical distribution on a larger scale. Tetroons were sent aloft with traps at 150', 100', 50' and at ground level. Results are preliminary, sex ratios approximated parity at all heights. Weights at all heights were similar (males weighing an average of 7.6 mg + 0.6, females 18.8 mg + 2.0). This seemed to be a function of being removed from host plants as weights increased (males weighing an average of 18.9 mg + 1.1, females 43.3 mg + 2.7) when insects were returned to host plants. 1996-7 Migration Publications 1. Byrne, D. N., R. J. Rathman, T. V. Orum and J. C. Palumbo. 1996. Localized migration and dispersal by the sweet potato whitefly, Bemisia tabaci. Oecologia 105: 320-328. 2. Byrne, D. N. and J. L. Blackmer. 1996. Examination of short-range migration by Bemisia. In D. Gerling and R. T. Mayer (eds.) Bemisia :1995 Taxonomy, Biology, Damage, Control and Management. pp. 17-28 Intercept Limited, Andover, UK. 3. Tu, Z., D. N. Byrne and H. H. Hagedorn. 1997. Vitellin of the sweet potato whitefly, Bemisia tabaci:: biochemical characterization and titer changes in the adult. Archives of Insect Biochemistry and Physiology 34: 223-237. 4. Veenstra, K. H. and D. N. Byrne. 1997. Effects of starvation and oviposition activity on the reproductive physiology of the sweet potato whitefly, Bemisia tabaci. Physiological Entomology, accepted. 5. Veenstra, K. H. and D. N. Byrne. 1997. Effects of starvation and oviposition activity on the reproductive physiology of the sweet potato whitefly, Bemisia tabaci. Physiological Entomology, accepted. 6. Isaacs, R. and Byrne, D. N. 1997. Aerial dispersal patterns, flight behavior and egg-load: their inter-relationship in the sweetpotato whitefly. Journal of Animal Ecology, tentatively accepted. 7. Veenstra, K. H. and D. N. Byrne. 1997. Behavioral aspects of dispersal by Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae). Journal of Insect Behavior, submitted. 8. Blackmer, J. L. and D. N. Byrne. 1997. The effect of Bemisia argentifolii on amino acid balance in Cucumis melo. Entomologia Experimentalis et Applicata, submitted. 9. Blackmer, J. L. and D. N. Byrne. 1997. The role of plant amino acids in determining life-history traits and flight propensity in Bemisia tabaci (Homoptera: Aleyrodidae). Entomologia Experimentalis et Applicata, submitted. 10. Veenstra, K. H. and D. N. Byrne. 1997. Does dispersal affect the reproductive physiology of the sweet potato whitefly, Bemisia tabaci?. Physiological Entomology, submitted. 11. Veenstra, K. H. and D. N. Byrne. 1997. The effects of physiological factors and host plant experience on the ovipositional activity of the sweet potato whitefly, Bemisia tabaci. Physiological Entomology, submitted. [ 1997 Research Index ]
Last updated 1 June, 2007 This page was constructed by Gail Kampmeier at gkamp[at]uiuc.edu Please direct questions of content and prospects of collaborative research to respective scientists. Research reports do not constitute publication and results may be preliminary. They are included here for informational purposes only. You should contact the authors for further information. Any references to commercial products do not constitute endorsement. [ NCR-148 \| Movement & Dispersal Index \| News Index ]

Dispersal of Bemisia tabaci

the Sweet Potato Whitefly,

& Members of its Parasitoid Complex

David N. Byrne*, Jacquelyn L. Blackmer#, David Bellamy*,
David Donnell*, Rufus Isaacs and Klaas H. Veenstra*

*Dept. of Entomology, University of Arizona, Tucson, AZ 85721 USA
#CCTA/UENF, Brazil
Dept. of Entomology, 203 Pesticide Research Center, Michigan State University, East Lansing, MI 48824 USA.

Abstract

This report focuses on the progress made during the last year in our laboratory's examination of short (<5.0 km) range migration of the sweet potato whitefly, Bemisia tabaci (Gennadius). We also report preliminary results of experiments concerning the whitefly parasitoid Eretmocerus eremicus. We are also investigating the vertical components of whitefly dispersal in the field. Preliminary results show the intense concentration of the flying population near to the ground. Also, marked whiteflies were routinely caught in the highest traps (7.2 m) on a series of trestles. This was true even in the trestles placed at the field edge. This indicates that a portion of the population dispersing from a field immediately rises to reasonably high altitudes. More recent work with traps suspended from balloons has shown that whiteflies can be captured at heights of at least 150' during early morning hours. Sex ratios and potential weights were similar regardless of the heights at which the whiteflies were captured. In a vertical flight chamber we found that E. eremicus, unlike B. tabaci., flew multiple times. Individuals as old as 21 days flew in the chamber. Additionally, females flew for considerably longer periods of time than did males. There was some response to a visual light cue (plant simulator), but not at the level seen previously with whiteflies.

Introduction

On a worldwide basis Bemisia tabaci (Gennadius), the sweet potato whitefly, continues to be one of the principle pests of crops grown for food and fiber. Because there are no viable alternatives to chemical control available (i.e., resistant varieties or profitable alternative crops), growers are left with one principle control strategy; the application of pesticides. It recent years there has been almost total reliance on the class of chemicals known as the chlornicotinyls. This is not environmentally sound nor does it insure long-term success. High levels of insecticides resistance has already been reported in parts of Europe and seem to exist the Southwest as well. We feel that a better understanding of whitefly dispersal behavior will lead to management strategies that are less pesticide dependent.

Additionally, our laboratory has recently been working to character the flight behavior of the whitefly parasitoid Eretmocerus. It seems that if individuals involved in biological control efforts are going to tout the use of refugia as a means of managing whitefly numbers then information concerning flight by these wasps would seem important.

During the last nine years, various members of our laboratory have examined what we term mid-range dispersal (by our definition on the scale of a few kilometers). The focus in this report is to discuss the progress made this last year concerning our understanding of short (< 1.0 km) and long-range (>5.0 km) dispersal by B. tabaci., in a large part by testing our hypotheses in the field.

Laboratory Experiments in 1996-7

Behavioral aspects
We examined the response by B. tabaci that had dispersed from agricultural fields (primarily melons) to visual stimuli. Whiteflies were, in general, strongly attracted to yellow placards, but displayed no response to single mature cotton plants that were presented as targets. Their response to yellow did not seem to be dependent upon distance traveled (from 0.7 to 2.1 km). The increase in numbers caught in traps with a yellow placard was negatively correlated with wind speed (from 1.0 to 5.0 m/s), but not with solar radiation or temperature. Dispersal in B. tabaci is apparently not entirely passive, but the ability to respond to vegetative stimuli likely decreases as wind speed increases. Evidence indicates that prevailing winds can interfere with the ability of B. tabaci to alight on potential hosts.

Physiological aspects

We examined the reproductive physiology of B. tabaci after their dispersal from cotton fields. In particular, we were interested in the synthesis of vitellogenins and the production of mature eggs. Whiteflies that dispersed out of fields, and were flying approximately 0.1 m above the soil surface, exhibited a reproductive physiology that was not significantly different from that exhibited by whiteflies that remained in cotton fields. B. tabaci captured in fan traps placed at 2.1 m matured eggs at a significantly lower rate. It appears that these latter whiteflies exhibit a physiology that indicates a reallocation of nutrients and energy resources in support of dispersal. We have attempted to measure similar traits in whiteflies caught at heights of 50, 100 and 150 m. This work is yet to be completed. We have found significant differences in sex ratios and weights that varied with height.

Parasitoid flight behavior

The dispersal abilities of the parasitoid Eretmocerus eremicus (Hymenoptera: Aphelinidae) were examined in a vertical flight chamber to determine its dispersal potential and to compare this to the flight behavior of B. tabaci (Hemiptera: Aleyrodidae). Individual wasps of known age and sex were placed on a raised platform in a vertical flight chamber (31" x 32" x 35") illuminated by a sodium-vapor light from above. Wasps were given two minutes to respond to the light by taking flight. Once airborne, timing of the flight began and a regulated air current was induced to model a vertical climb. Wasps were exposed to a ten second vegetative cue every sixty seconds while in flight to test their migratory state. Flight sessions ended when the wasps ceased flying for a period longer than two minutes. Preliminary results clearly indicate that there is a statistical difference in observed flight times in a vertical flight chamber between males (1 min. avg., 10 min. longest flight) and females (19 min. avg., 93 min. longest flight). Initial results also suggest that there exist two distinct populations within females of short-duration flyers (<20 min.) and long-duration flyers (>25 min.).

Field Experiments 1996-7
The aerial distribution of B. tabaci during the early ascent phase of flight was studied over two summers in southwestern Arizona, to test the possibility of making predictions about dispersal patterns from our understanding of flight behaviors. Marked whiteflies were trapped at four heights between 0 and 7.27 m above fallow ground, and at six distances between 0 to 100 m from the insect source. Insects were trapped during a 2-3 h period after the initiation of flight activity during parts of 1995 and 1996. Analysis of the trap catch data revealed a clear negative exponential relationship between height and aerial distribution, and a slightly weaker negative power relationship between distance and aerial distribution. Marked insects were caught in the uppermost traps adjacent to the source, indicating that a portion of the population has a strong capacity for ascent out of the flight boundary layer. Egg-load decreased with the height, but not the distance, at which B. tabaci was trapped. Mean egg load close to the ground was significantly greater than that for those trapped at 4.8 and 7.2 m, supporting the hypothesis that there is a trade-off between flight and oogenesis in weak-flying insects. Air temperatures during the trapping periods were positively correlated with the proportion of male and female B. tabaci caught in the highest traps, but not in the most distant traps. The significance of these results for accurate prediction of whitefly dispersal is discussed, and the importance of individuals behavior in determining dispersal patterns of small insects is emphasized.

We also examined vertical distribution on a larger scale. Tetroons were sent aloft with traps at 150', 100', 50' and at ground level. Results are preliminary, sex ratios approximated parity at all heights. Weights at all heights were similar (males weighing an average of 7.6 mg + 0.6, females 18.8 mg + 2.0). This seemed to be a function of being removed from host plants as weights increased (males weighing an average of 18.9 mg + 1.1, females 43.3 mg + 2.7) when insects were returned to host plants.

1996-7 Migration Publications

1. Byrne, D. N., R. J. Rathman, T. V. Orum and J. C. Palumbo. 1996. Localized migration and dispersal by the sweet potato whitefly, Bemisia tabaci. Oecologia 105: 320-328.

2. Byrne, D. N. and J. L. Blackmer. 1996. Examination of short-range migration by Bemisia. In D. Gerling and R. T. Mayer (eds.) Bemisia :1995 Taxonomy, Biology, Damage, Control and Management. pp. 17-28 Intercept Limited, Andover, UK.

3. Tu, Z., D. N. Byrne and H. H. Hagedorn. 1997. Vitellin of the sweet potato whitefly, Bemisia tabaci:: biochemical characterization and titer changes in the adult. Archives of Insect Biochemistry and Physiology 34: 223-237.

4. Veenstra, K. H. and D. N. Byrne. 1997. Effects of starvation and oviposition activity on the reproductive physiology of the sweet potato whitefly, Bemisia tabaci. Physiological Entomology, accepted.

5. Veenstra, K. H. and D. N. Byrne. 1997. Effects of starvation and oviposition activity on the reproductive physiology of the sweet potato whitefly, Bemisia tabaci. Physiological Entomology, accepted.

6. Isaacs, R. and Byrne, D. N. 1997. Aerial dispersal patterns, flight behavior and egg-load: their inter-relationship in the sweetpotato whitefly. Journal of Animal Ecology, tentatively accepted.

7. Veenstra, K. H. and D. N. Byrne. 1997. Behavioral aspects of dispersal by Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae). Journal of Insect Behavior, submitted.

8. Blackmer, J. L. and D. N. Byrne. 1997. The effect of Bemisia argentifolii on amino acid balance in Cucumis melo. Entomologia Experimentalis et Applicata, submitted.

9. Blackmer, J. L. and D. N. Byrne. 1997. The role of plant amino acids in determining life-history traits and flight propensity in Bemisia tabaci (Homoptera: Aleyrodidae). Entomologia Experimentalis et Applicata, submitted.

10. Veenstra, K. H. and D. N. Byrne. 1997. Does dispersal affect the reproductive physiology of the sweet potato whitefly, Bemisia tabaci?. Physiological Entomology, submitted.

11. Veenstra, K. H. and D. N. Byrne. 1997. The effects of physiological factors and host plant experience on the ovipositional activity of the sweet potato whitefly, Bemisia tabaci. Physiological Entomology, submitted.

[ 1997 Research Index ]