Olfactory Basis of Moth-Hostplant Interactions

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4NSF IBN-9983302 8 February 2000Lay Abstract This research focuses on determining how female moths use their sense of smell to find appropriate plants on which to lay their eggs. We study an experimentally favorable and extensively investigated model insect, the tobacco hornworm moth Manduca sexta. Because little is known about hostplant finding by female moths, and in particular which compounds released by plants facilitate this interaction between moths and their specific hostplants, this research comprises two main tasks: (a) chemical separation of volatile compounds ("plant volatiles") collected from the air surrounding living plants, and (b) behavioral testing of the responses of female moths to these hostplant volatiles under controlled laboratory conditions. In the next year of this research, we will focus on utilizing a chemical separation technique called preparative gas-chromatography (GC) to fractionate headspace-volatile mixtures obtained from living plants and on testing the behavioral responses of adult female M. sexta moths to the isolated fractions. Currently we are constructing a special fraction collector that will allow us to trap volatile compounds separated by GC as they emerge from the GC column. As a fraction emerging from the GC column pass into a cooled collection tube in the fraction collector, the volatile compounds in the fraction will be trapped. The isolated fraction then can be tested for its effects on the flight behavior of female moths, in the laboratory, and if the fraction elicits appropriate behaviors, compounds making up that fraction will be identified by means of GC coupled with mass spectroscopy (GC-MS). We will focus on using one hostplant species, named devil's claw (Proboscidea louisianica var. fragrans), and one non-hostplant species, foliage of potato plants (Solanum tuberosum). Headspace-volatiles from potato foliage trigger strong behavioral responses in the moths both in the flight tunnel and in a bench-top bioassay that tests abdomen-curling responses (a simple behavior that immediately precedes egg-laying). Potato plants are closely related to hostplants of M. sexta and are attractive to female moths, but these plants are not good hostplants themselves because they are rejected for oviposition after a female moth has contacted the leaves of the plant. From our previous work in this project, we know that the behavioral responses of female moths to the volatiles released by greenhouse-grown potato plants are stronger than behavioral responses to several documented hostplants. Devil's claw plants are not related to the previously known hostplants of M. sexta, but we recently found that this plant is a surprisingly good hostplant nevertheless. We expect that both of these plant species, whose volatiles elicit strong behavioral responses from the female moths, will emit the same or very similar behaviorally active volatile compounds. By studying and comparing their volatiles and the behavioral effects those compounds elicit, we furthermore expect to be able to discover what volatile compounds are responsible for the attractiveness of hostplants. Because our research plan is directed toward obtaining publishable results within one year, our goal will be to focus on volatiles that elicit one of the two key behavioral responses that are elicited by hostplants and volatiles collected from them -- either odor-modulated upwind flight or the abdomen- curling behavior that precedes egg-laying.