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Project description

The Isolation and Characterization of Squash Bug, Anasa tristis, Pheromones and the Development of a Management Program Using Pheromones in Mating Disruption. (99DS023)
Program UC IPM competitive research grants program
Principal
investigators
C.G. Summers, Entomology, UC Riverside
J.G. Millar, Entomology, UC Riverside
Host/habitat Cucurbits
Pest Squash Bug Anasa tristis
Discipline Entomology
Review
panel
Decision Support
Start year (duration)  1999 (Three Years)
Objectives Determine basic biological and behavioral parameters of squash bug which are important in the identification and use of pheromones as management tools and to obtain preliminary data on the existence of a squash bug pheromone(s).

Identify, synthesize, and test sex or aggregation pheromones of the squash bug.

Develop pheromone-based management strategies for the squash bug.

Final report Evaluated the possible production of a sex pheromone in squash bugs by a field bioassays technique using live, laboratory reared squash bugs of known age. Our studies indicate that squash bugs do not mature sexually until 8 to 10 days following their molt to the adult stage. In our field bioassays, virgin males and females (8-12 days old) were placed in a trap-cage and the trap-cages placed in a zucchini squash field for 24 hours. In 12 separate tests, we caught a total of 136 males in traps that had been baited with virgin females. Three females were caught in those same traps. The traps in which the females were caught had remained in the field for 72 hours, and we speculate that during that extended time period, the females crawled in by accident. No females, however, were ever caught in traps baited with virgin males of any age. These data clearly indicated that virgin females produce a volatile compound(s) that attracted the males. This information was then used to isolate volatile compounds from the bugs under laboratory conditions. Volatile compounds were collected from 10-day-old virgin males and females. Comparisons of the profiles of each of these volatiles obtained from males and females revealed that undisturbed females released at least two compounds which neither of which were seen in male extracts.

Extracts prepared from immature insects and from sexually immature and mature virgin adults were analyzed. The exuvia from last instar bugs contained (E)-2-hexenal, (E)-4-oxo-2-hexenal, (Z)-4-oxo-2-hexenal in a ratio of 100: 82: 1, and traces of (E)-2-octenal. These compounds are all known defensive compounds for true bugs. Analyses of aeration extracts from undisturbed virgin males and females determined that females tended to produce more odors than males, but there were no compounds that were consistently found to be produced only be females (the attractive sex in field tests with live females as lures). Aerations from males frequently contained little or no material, whereas female extracts always contained several compounds. Further concentration of the female extracts and reanalysis revealed trace amounts of acetophenone, 1-undecene, undecane, hexyl propionate, hexyl butyrate, dodecane, octyl acetate, 2-undecanone, 2- dodecanone, tetradecane, and several compounds that have not yet been identified.

Overall, there was no clear pattern of the onset of production of compounds by males or females as they became sexually mature. There was also no obvious difference between the extracts prepared from aerations of females only, and females and males in the same aeration chamber, but separated by a screen. Hexanal and hexyl acetate were the two most prominent compounds in those extracts. Furthermore, once the screen was removed, males and females began mating virtually immediately, clearly indicating that they were in the correct physiological state to mate, and presumably producing pheromones. None of the test treatments attracted any male squash bugs to the sticky traps. Thus, the major component in bug extracts, hexyl acetate, is clearly not attractive alone. Furthermore, the reconstructed female blend was not attractive, indicating that the activity of the blend was being masked by some of the other components, or that one or more of the active components were missing.

Second-year
progress
Extracts prepared from immature insects and from sexually immature and mature virgin adults were analyzed. The exuvia from last instar bugs contained (E)-2-hexenal, (E)-4-oxo-2-hexenal, (Z)-4-oxo-2-hexenal in a ratio of 100: 82: 1, and traces of (E)-2-octenal. These compounds are all known defensive compounds for true bugs. Analyses of aeration extracts from undisturbed virgin males and females determined that females tended to produce more odors than males, but there were no compounds that were consistently found to be produced only be females (the attractive sex in field tests with live females as lures). Aerations from males frequently contained little or no material, whereas female extracts always contained several compounds. Further concentration of the female extracts and reanalysis revealed trace amounts of acetophenone, 1-undecene, undecane, hexyl propionate, hexyl butyrate, dodecane, octyl acetate, 2-undecanone, 2- dodecanone, tetradecane, and several compounds that have not yet been identified.

Overall, there was no clear pattern of the onset of production of compounds by males or females as they became sexually mature. There was also no obvious difference between the extracts prepared from aerations of females only, and females and males in the same aeration chamber, but separated by a screen. Hexanal and hexyl acetate were the two most prominent compounds in those extracts. Furthermore, once the screen was removed, males and females began mating virtually immediately, clearly indicating that they were in the correct physiological state to mate, and presumably producing pheromones.

None of the test treatments attracted any male squash bugs to the sticky traps. Thus, the major component in bug extracts, hexyl acetate, is clearly not attractive alone. Furthermore, the reconstructed female blend was not attractive, indicating that the activity of the blend was being masked by some of the other components, or that one or more of the active components were missing. In particular, we did not include hexanal in the blend because this compound is highly volatile and irritating, and it is normally used in the defensive secretions of bugs. However, at appropriate doses, it may indeed be a component of the attractive blend. We will attempt to retest new blends with hexanal added in lab bioassays over the winter.

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