Electroantennogram Responses

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Introduction

Bostrichid beetles are generally wood and twig borers, but species in three genera Prostephanus truncatus (Horn), Dinoderus bifoveolatus (Wollaston), and Rhyzopertha dominica (F.), have become facultatively associated with stored cereals, dried starchy tubers, and milled products. In West Africa, Dinoderus bifoveolatus may be found infesting dried cassava chips (Borgemeister et al, 2000). P. truncatus is widely distributed in México and Central America while Rhyzopertha dominica is a pest of stored wheat and other small grains worldwide (reviewed in Edde and Phillips 2006). Large aggregations of both sexes may form in stored products bostrichid pests in response to pheromones from signaling individuals, usually males (Borgemeister et al, 2000, Hodges 2002, Khorramshahi and Burkholder, 1981).

R. dominica aggregation pheromones were identified as (S)-(+)-1-methylbutyl (E)-2-methyl-2-pentenoate and (S)-(+)-1-methylbutyl (E)-2,4-dimethyl-2-pentenoate, commonly called Dominicalure-1 (DL-1) and Dominicalure-2 (DL-2), respectively (Williams et al., 1981; Khorramshahi and Burkholder, 1981). These male-produced pheromones are only released during feeding and volatile emissions from other insect or plant species are not known to contain DL-1 or DL-2. Field tests with synthetic dominicalure conducted in or near grain storages (Cogburn et. al. 1984, Leo-Martinez et al 1987) and in olfactometer experiments (Khorramshahi and Burkholder, 1981, Dowdy 1993) showed that there was no difference in responses by the beetles to the two compounds, individually and in combination. Captured R. dominica was female-biased in olfactometer studies or in aerial traps baited with mixtures of the two compounds (e.g. Bashir et al 2001, Edde et ...

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...imilar behavioral responses on both sexes of the beetle, but attractions increased with dosage (ref), indicating that these pheromones are behaviorally redundant, i.e. each functions as a fail-safe insurance for the other. Hence, males of this species produce two aggregation pheromones. The logical problem with the assumption of a single multi-component pheromone, and thus referring to each separate chemical as a “pheromone component”, as entomologists believed, is that there are several examples in which a host plant volatile is a synergist to insect produced pheromones. The insect produced compounds, pheromones, are only active against members of the insect species, but the required plant volatile cannot be called a pheromone since it is an interspecific semiochemical, and thus is a kairomone. These definitions have been discussed by Nordlund and Lewis (1981).

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