Developing sustainable pest control from chemical ecology

Alate and apterous virginoparae ofAphis fabae Scop, and alate virginoparae ofBrevicoryne brassicae (L.), walking in a linear track olfactometer, were attracted by odor from leaves of their host plants.A. fabae responded to odor from undamaged but not damaged bean leaves. Gynoparae (autumn migrants) ofA. fabae, however, did not respond to their host plant (spindle,Euonymus europaeus) odor. Odors of certain nonhost plants masked the attractiveness of the host plant leaves, but tansy (Tanacetum vulgare) and summer savory (Satureja hortensis) volatiles repelledB. brassicae andA. fabae, respectively. 3-Butenyl isothiocyanate attractedB. brassicae andLipaphis erysimi (Kalt.), the latter species being more sensitive in both behavioral and electrophysiological studies. Isothiocyanate receptors were found on the antennae ofA. fabae, which was repelled by these compounds, 4-pentenyl isothiocyanate being the most active.

Considerable basic information has been gathered on the interaction between the onion fly (Delia antiqua) and its host plant, the onion (Allium cepa). An attempt is underway to manipulate ovipositional behavior of this pest by treating onion seedlings with chemical deterrents while simultaneously providing deeply planted onion culls on which onion flies prefer to lay. This bipolar strategy of behavioral manipulation, termed "stimulo-deterrent diversion" (SDD), has the advantages of: (1) avoiding severe pest deprival and concomitant overriding of deterrents, (2) combining the effects of "push" and "pull" multiplicatively, and (3) providing opportunities for enhanced biological control in sites where the pest becomes concentrated. The suggestion is made that using SDD along with soil insecticide might relax or even reverse selection for physiological resistance ofD. antiqua to insecticides. As tools of molecular biology open new possibilities for manipulating plants and their allelochemicals, applied chemical ecologists should consider arranging situations where the allelochemicals have clear and adaptive messages for the pest. By combining toxins and deterrents at sites where feeding should be prevented, while simultaneously expediting use of alternative plants or plant parts, it might be possible to guide pest evolution toward paths of less conflict with human interest.