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Title: PHEROMONES OF MILKWEED BUGS ( HETEROPTERA: LYGAEIDAE) ATTRACT WAYWARD PLANT BUGS

Author
item ZHANG, QING-HE - UNIV. OF MD DEPT OF ENTOM
item Aldrich, Jeffrey

Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/28/2003
Publication Date: N/A
Citation: N/A

Interpretive Summary: There are over 10,000 species of plant bugs in the family Miridae, and many feed on the flowers, fruit and buds of crop plants causing plant deformation and fruit abortion. In spite of their importance as pests, methods for sampling and monitoring plant bug populations are relatively primitive, essentially relying on hand sampling. Here we report the identification of chemical attractants (sex pheromones) for two plant bugs, Phytocoris difficilis and P. breviusculus. The sex pheromones of these plant bugs are composed of inexpensive, commercially available chemicals, and the insects are common in mixed pine/oak forests in the United States. These research results will be most useful as a model system for scientists studying this group of economically important insects.

Technical Abstract: The synthetically reconstructed aggregation pheromone of the large milkweed bug, Oncopeltus fasciatus (Dallas) (Lygaeinae), revealed thatalso attractsed males of the plant bug, Phytocoris difficilis Knight (Miridae)in mid-summer and early fall males of the mirid bug, Phytocoris difficilis Knight., were also highly attracted. Field-testing partial blends against the six-component blend comprising the Oncopeltus pheromone showed that cross-attraction of P. difficilis males was due to a synergism between (E)-2-octenyl acetate and (E,E)-2,4-hexadienyl acetate. Females of two Phytocoris species in the western United States (Millar et al., 1997; Millar and Rice, 1998)[Millar, 1997 #63;Millar, 1998 #64] produce (E)-2-hexenyl and (E)-2-octenyl acetates, which are also in the milkweed bug pheromone, while hexyl acetate (not part of the Oncopeltus pheromone) is produced by both sexes of western Phytocoris spp. and is an essential pheromone component of each species. However, western Phytocoris spp. do not produce (E,E)-2,4-hexadienyl acetate. Gas chromatographic-mass spectrometric (GC-MS) analysis showed that hexyl acetate is a major component ofabundant in the metathoracic scent gland (MSG) secretion of P. difficilis males. , but Ssince female P. difficilis could not initially be found in the field, further combinatorial tests were guided by prior research on the pheromones including hexyl and (E)-2-hexenyl acetates with (E)-2-octenyl acetate were conductedof two Phytocoris species in the western United States (Millar et al., 1997; Millar and Rice, 1998). The combination of hexyl, (E)-2-hexenyl and (E)-2-octenyl acetates was as attractive to P. difficilis males as was the milkweed bug pheromone, yet no milkweed bugs were drawn to this blend. Eventually, two live P. difficilis females attracted to a black light were collected and, using GC-electroantennographic detection (EAD) and GC--MS, analysis of female P. difficilis female MSGs it was determined that their MSG secretion contained three major constituentspredominantly (all strongly EAD-active), hexyl, (E)-2-hexenyl and (E)-2-octenyl acetates (all strongly EAD-active)¿the latter two compounds found only in trace amounts from males¿plus five minor female-specific compounds, three of which were EAD-active. (E,E)-2,4-Hexadienyl acetate was not undetectedable from P. difficilis females and males. The blend of the three major components, hexyl, (E)-2-hexenyl and (E)-2-octenyl acetates (2: 1.5 :1 by volume), was as active attractive as the blend of all six EAD-active compounds identified from females, and this ternary blend constitutes the sex pheromone of P. difficilis. Interestingly, hexyl acetate with (E)-2-octenyl acetate attracted males of another species, P. breviusculus Reuter, but while addition of (E)-2-hexenyl acetate and/or (E,E)-2,4-hexadienyl acetate was antagonisticinhibited attraction of P. breviusculus males. Attraction of males P. difficilisfor each of these Phytocoris malesspp. occurred peaked mainly during the first half ofin early scotophase. The possible neurophysiological basis for this asymmetrical cross-attraction is discussed.