Robert R. Heath

Isolation and identification of allelochemicals that attract the larval parasitoid, Cotesia marginiventris (Cresson), to the microhabitat of one of its hosts

Volatiles released from corn seedlings on which beet armyworm larvae were feeding were attractive to females of the parasitoid,Cotesia marginiventris (Cresson), in flight tunnel bioassays. Analyses of the collected volatiles revealed the consistent presence of 11 compounds in significant amounts. They were: (Z)-3-hexenal, (E)-2-hexenal, (Z)-3-hexen-1-ol, (Z)- 3-hexen-1-yl acetate, linalool, (3E)-4,8-dimethyl-1,3,7-nonatriene, indole, α-trans-bergamotene, (E)-β-farnesene, (E)-nerolidol, and (3E,7E)-4,8,12-trimethyl-1, 3,7,ll-tridecatetraene. A synthetic blend of all 11 compounds was slightly less attractive to parasitoid females than an equivalent natural blend. However, preflight experience with the synthetic blend instead of experience with a regular plant-host complex significantly improved the response to the synthetic blend. Our results suggest thatC. marginiventris females, in their search for hosts, use a blend of airborne semiochemicals emitted by plants on which their hosts feed. The response to a particular odor blend dramatically increases after a parasitoid experiences it in association with contacting host by-products.

Volatiles emitted by different cotton varieties damaged by feeding beet armyworm larvae.

Volatile compounds elicited by insect herbivore feeding damage in five cotton cultivars and one naturalized cotton variety were examined by allowing beet armyworm larvae to feed overnight on leaves and collecting volatiles from the plants in situ. Of 23 compounds identified from larval damaged leaves, terpenes and lipoxygenase-hydroperoxide lyase-derived volatiles predominated. No pronounced differences in the levels of volatile emission were noted from leaves of undamaged plants of the different varieties. However, average volatile emission from damaged leaves of the naturalized variety was almost sevenfold higher than from damaged leaves of the commercial cultivars. This was despite the fact that larvae preferred feeding on the leaves of commercial cultivars over those of the naturalized variety in choice tests.

Volatile Semiochemicals Released from Undamaged Cotton Leaves (A Systemic Response of Living Plants to Caterpillar Damage).

Cotton plants (Gossypium hirsutum L.), attacked by herbivorous insects release volatile semiochemicals (chemical signals) that attract natural enemies of the herbivores to the damaged plants. We found chemical evidence that volatiles are released not only at the damaged site but from the entire cotton plant. The release of volatiles was detected from upper, undamaged leaves after 2 to 3 d of continuous larval damage on lower leaves of the same plant. Compounds released systemically were (Z)-3-hexenyl acetate, (E)-[beta]-ocimene, linalool, (E)-4,8-dimethyl-1,3,7-nonatriene, (E)-[beta]-farnesene, (E,E)-[alpha]-farnesene, and (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene. All systemically released compounds are known to be induced by caterpillar damage and are not released in significant amounts by undamaged plants. Other compounds, specifically indole, isomeric hexenyl butyrates, and 2-methylbutyrates, known to be released by cotton in response to caterpillar damage, were not released systemically. However, when upper, undamaged leaves of a caterpillar-damaged plant were damaged with a razor blade, they released isomeric hexenyl butyrates, 2-methylbutyrates, and large amounts of constitutive compounds in addition to the previously detected induced compounds. Control plants, damaged with a razor blade in the same way, did not release isomeric hexenyl butyrates or 2-methylbutyrates and released significantly smaller amounts of constitutive compounds. Indole was not released systemically, even after artificial damage.

Development and evaluation of systems to collect volatile semiochemicals from insects and plants using a charcoal-infused medium for air purification.

A system is described for the collection of volatiles produced by plants and insects that minimizes stresses on the plant or insect in an environment that is free from chemical impurities. Air entering a volatile collection chamber containing insects and/or plants was purified using a nonwoven fabric medium infused with charcoal. When three layers of this material were used, the total amount of impurities detected by gas chromatography was less than 40 ng/hr at a collection rate of 1 L/min. The air filtration system can maintain this level of air purification for 96 hr at an air flow of 0.43 m/sec, or a total volume of approximately 750,000 L of air. The air filtration system did not alter the relative humidity of the purified air compared to the relative humidity of ambient air. A multiport collector system was developed for use with the insect volatile collection system and enabled up to three samples to be collected without disturbing the system.

Sex Pheromones and Reproductive Isolation of the Lesser Peachtree Borer and the Peachtree Borer

(E,Z)-3,13-octadecadien-1-ol acetate, and (Z,Z)-3,13-octadecadien-1-ol acetate, isolated from the female lesser peachtree borer, Synanthedon pictipes (Grote and Robinson), and the female peachtree borer, Sanninoidea exitiosa (Say), respectively, strongly attract the respective males of these species in field bioassays. These compounds are the largest pheromones isolated thus far from a lepidopterous species. Sanninoidea exitiosa males did not respond to the synthesized (E,Z)-isomer, and low concentrations of it in the synthesized (Z,Z)-isomer did not interfere with their response to the (Z,Z)-isomer. In contrast, even very low concentrations of the (Z,Z)-isomer (1 percent) in the (E,Z)-isomer significantly inhibited the response of Synanthedon pictipes males.

Chemical and behavioral analyses of volatile sex pheromone components released by callingHeliothis virescens (F.) females (Lepidoptera: Noctuidae).

Gas chromatographic and mass spectral analyses were conducted on pheromone gland extracts, volatiles collected from excised pheromone glands, and volatiles collected from calling females. In addition to tetradecanal, (Z)-9-tetradecenal, hexadecanal, (Z)-7-hexadecenal, (Z)-9-hexadecenal, and (Z)-11-hexadecenal, four other compounds, tetradecanol, (Z)-9-tetradecenol, hexadecanol, and (Z)-11-hexadecenol, were also identified from gland extracts. Only the six aldehyde components were found in gland and female volatile collections. The mean percentage of components identified from volatiles collected from calling females was 13.0% tetradecanal, 18.1% (Z)-9-tetradecenal, 7.3% hexadecanal, 0.6% (Z)-7-hexadecenal, 1.0% (Z)-9-hexadecenal, and 60.0% (Z)-11-hexadecenal. Bioassays using rubber septa formulated to release the female volatile blend indicated that all six aldehyde components play major roles in close-range male reproductive behavior. Deletion of (Z)-9-hexadecenal from the six-component blend reduced the number of copulation attempts while (Z)-7-hexadecenal exerted subtle effects on all close range behaviors. Tetradecanal affected the number of times males reorient from close range. Deletion of hexadecanal from the six-component blend resulted in a significant reduction in the number of times males landed. Comparison of the six-component synthetic blend (released at somewhat less than 1 female equivalent per hour) with calling females indicated that the six-component blend was indistinguishable from the females in inducing all of the behaviors monitored.

Chemical Mimicry: Bolas Spiders Emit Components of Moth Prey Species Sex Pheromones

Field studies have indicated that bolas spiders attract male moth prey, apparently by mimicking the odor of female moth sex pheromones. Three moth sex pheromone compounds, (Z)-9-tetradecenyl acetate, (Z)-9-tetradecenal, and (Z)-11-hexadecenal, were identified in volatile substances emitted by hunting adult female Mastophora cornigera spiders. These compounds are components of pheromone blends that attract some of this spiders moth prey species.

TRAP-LURE COMBINATIONS FOR SURVEILLANCE OF ANASTREPHA FRUIT FLIES (DIPTERA: TEPHRITIDAE)

Trap/lure combinations were tested against populations of Anastrepha suspensa (Loew) and Anastrepha ludens (Loew) as substitutes for the traditional glass McPhail trap. Open-bottom, plastic traps baited with a two component synthetic lure (ammonium acetate and putrescine) caught as many and sometimes more fruit flies than the McPhail trap baited with torula yeast. Sex ratio of flies caught with the synthetic lure was similar to that caught with torula yeast, i.e., generally female biased, but variable among seasons and locations. The synthetic lure attracted fewer non-target insects giving a substantial time savings in trap maintenance. Moreover, the synthetic lure was effective for ten weeks without replacement. Propylene glycol antifreeze increased captures significantly and improved preservation of specimens when used as the trap liquid compared to water. Dry jar traps and cardboard sticky traps were ineffective in comparison with the liquid baited traps.

Identification of a sex pheromone ofHeliothis subflexa (GN.) (Lepidoptera: Noctuidae) and field trapping studies using different blends of components.

Eight compounds were isolated from the sex pheromone gland ofHeliothis subflexa (Gn.) and identified as hexadecanal, (Z)-9-hexadecenal, (Z)-11-hexadecenal, (Z)-7-hexadecen-1-ol acetate, (Z)-9-hexadecen-1-ol acetate, (Z)-11-hexadecen-1-ol acetate, (Z)-9-hexadecen-1-ol, and (Z)-11-hexadecen-1-ol. Although the whole blend was found to be an effective male attractant, the deletion of alcohols from the blend increased trap captures considerably. Further, although the binary mixture of (Z)-9-hexadecenal and (Z)-11-hexadecenal caught some maleH. subflexa, significant increases in captures were noted when the three acetate components were included in the blend.

Prediction of release ratios of multicomponent pheromones from rubber septa

A method has been developed to predict the release ratio of the components of blends of alcohols, acetates, and/or aldehydes from rubber septa. The calculations of predicted release ratios are based on the relative vapor pressures of the components. The relative vapor pressures of the compounds were calculated from their retention indices on a liquid crystal capillary gas chromatographie column. The correlation between the theoretically predicted and experimentally determined ratios was very good. Thus, formulations can be prepared that will release a desired ratio of the components of a multicomponent pheromone blend.