Rl. Metcalf et al., INDOLE AS AN OLFACTORY SYNERGIST FOR VOLATILE KAIROMONES FOR DIABROTICITE BEETLES, Journal of chemical ecology, 21(8), 1995, pp. 1149-1162
Olfactory synergism, where combinations of plant volatile kairomones a
re quantitatively more attractive to insects than the sum of attractio
n of the individual components, is an important but little-studied phe
nomenon in host plant selection and feeding and in pollination ecology
. Diabroticite beetles (Coleoptera: Chrysomelidae) are strongly attrac
ted to Cucurbita blossoms, and 2- to 5-fold olfactory synergism has be
en demonstrated in four species by combinations of the key blossom vol
atiles, 1,2,4-trimethoxybenzene, indole, and (E)-cinnamaldehyde, This
TIC mixture represents an optimized Curcurbita blossom volatile kairom
one mixture useful in monitoring Diabroticite populations and in study
ing their behavior and ecology. Indole, which exhibits a spectrum of a
ttraction to these beetles ranging from moderate for Diabrotica virgif
era virgifera and Acalymma vittatum to very weak for D. barberi, is th
e primary synergistic component. Indole combined with 4-methoxycinnama
ldehyde was significantly synergistic to D. v. virgifera at a ratio of
1:300 and produced 4-fold synergism at a ratio of 1:1. Indole combine
d with 4-methoxyphenethanol was less synergistic to D. barberi with 1.
5- to 2-fold synergism at a 1:1 ratio. These consistent variations in
diabroticite beetle olfactory responses presumably indicate evolutiona
ry divergences in the numbers of relict indole antennal receptors.