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Title: ATTRACTION OF SCAVENGING CHLOROPID AND MILICHIID FLIES (DIPTERA) TO METATHORACIC SCENT GLAND COMPOUNDS OF PLANT BUGS (HETEROPTERA: MIRIDAE)

Author
item Aldrich, Jeffrey
item ZHANG, QINE-HE - DEPT. OF ENTOM. UMD

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/28/2003
Publication Date: 2/1/2004
Citation: Aldrich, J.R., Zhang, Q. 2004. Attraction of scavenging chloropid and milichiid flies (diptera) to metathoracic scent gland compounds of plant bugs (heteroptera: miridae). Environmental Entomology. 33(1):12-20.

Interpretive Summary: The tarnished plant bug is an important pest of many crops in the United States. We are identifying the sex attractant produced by this bug in order to develop safe methods of controlling it. In a study done to identify these attractants, traps were baited with chemical compounds commonly produced in the scent glands of the tarnished plant bug and related bugs. Surprisingly, we found that large numbers of small flies called grass flies were attracted to the traps. This group of flies includes immature stages that damage wheat and barley; adults usually lay their eggs on plants or decaying plant material but can feed on dead bugs. Only female flies were attracted, particularly to two simple chemical compounds. The results indicate that when a bug dies, the volatile chemicals begin leaking from the corpse, and the flies use these volatile compounds as signals to find dead bugs on which to feed. The results are significant because they indicate that female flies need a protein-rich meal for maximum egg production, similar to the necessity of female mosquitoes to feed on blood in order to develop eggs. This is the first realization that this group of flies needs to feed on protein before going to their host plants to lay eggs. The information will be used by researchers monitoring bug and fly pest species with chemically baited traps and developing safe controls by combining chemical attractants with insecticidal baits.

Technical Abstract: Hexyl butyrate and (E)-2-hexyl butyrate, common metathoracic scent gland compounds of plant bugs (Heteroptera: Miridae), attracted large numbers of female chloropid (Olcella trigramma, O. cinerea, Conioscinella sp.) and milichiid (Leptometopa latipes) flies. Blends of these two butyrates attracted significantly more chloropids than did the compounds individually. The optimal synergistic ratios for O. trigramma attraction ranged from 1:1 to 9:1 hexyl butyrate to hexenyl butyrate, similar to natural ratios of these compounds in the scent gland secretion from tarnished plant bugs, Lygus lineolaris, and other mirids. Conioscinella females exhibited similar dose-response curves to hexyl and (E)-2-hexenyl butyrates, with a threshold for attraction to these esters at about the same amount normally produced by an individual plant bug. (E)-2-octenyl acetate, one of the major sex pheromone components of mirids in the genus Phytocoris, was strongly attractive to the milichiid, L. latipes, and weakly, but significantly attractive to the chloropids, O. trigramma, O. cinerea and Conioscinella sp. Another pheromone component of Phytocoris bugs, hexyl acetate, was inactive by itself, yet synergized the attraction of the milichiid and three chloropid species to (E)-2-octenyl acetate. Traps baited with (E)-2-hexenyl (E)-2-hexenoate, a volatile component of various heteropterans, was significantly attractive to both O. cinerea and L. latipes, while addition of g-caprolactone or green leaf alcohols significantly reduced the numbers of both fly species caught. In an electroantennogram study, O. trigramma female antennae strongly responded to (E)-2-hexyl butyrate and, to a lesser degree, to hexyl butyrate, while electroantennogram responses to butyl butyrate and pentyl butyrate were not significantly different from the blank control. Our results suggest that females of these chloropid and milichiid flies use volatile defensive and pheromonal compounds from plant bugs as kairomones to find freshly dead bugs on which to feed. The sex-specific attraction suggests that females of these flies need a protein-rich meal for maximum fecundity, similar to anautogenous mosquitoes.