Behavioral Responses of Adult Sitophilus granarius to Individual Cereal Volatiles

Abstract

The antennae of Sitophilus granarius (L.) (Coleoptera: Curculionidae) adults detect a wide variety of compounds in the odor blend of various cereal grains (Germinara et al., Tec. Molit., 53:27-34, 2002). In the present study, we looked at the behavioral responses of the granary weevil to 20 of these individual volatiles (aliphatic alcohols, aldehydes, ketones, and aromatics) in a two-choice pitfall olfactometer, using the aggregation pheromone and propionic acid as the attractant and repellent controls, respectively. Five doses, ranging from 1 microg to 1 mg, of each compound were tested. At least one concentration of eight compounds attracted beetles but required doses 1,000- to 5,000-fold higher than the concentration of aggregation pheromone to elicit a response. Three compounds, while attractive at lower concentrations, acted as repellents at higher doses. Twelve compounds were repellent at concentrations similar to the quantity of propionic acid that significantly repelled beetles. The data show that granary weevil adults have the ability to respond behaviorally to a wide range of cereal volatiles and that responses may change as a function of concentration. The results suggest that host finding behavior of weevils will depend on the balance of positive and negative volatile stimuli from grain as the relative concentrations of volatiles may change during storage. An understanding of how the weevils respond to such changes could be useful for the development of effective integrated pest management strategies.

Repellents effectively disrupt the olfactory orientation of Sitophilus granarius to wheat kernels

“…Some volatile aldehydes and hexanol, known to be emitted by grains of different cereal species (Maga 1978), showed repellent activity towards granary weevil adults when individually tested in the absence of a suitable host odor source (Germinara et al 2008). In this study, hexanol, butanal, hexanal, (E)-2-hexenal, heptanal, (E,E)-2,4-nonadienal, (E,E)-2,4-decadienal, furfural, in the dose range previously tested (from 1 to 1000 lg), were assessed for their ability to disrupt olfactory orientation of insects to In a row, significant differences between treatment and control responses are indicated by Student's t-test (P \ 0.05).…”

“…Test compounds selected on the basis of their repellent activity towards granary weevil adults (Germinara et al 2008) Cat. No.…”

“…A two-choice pit-fall bioassay similar to that described in previous studies (Phillips et al 1993;Germinara et al 2008) was adopted to evaluate the ability of each test compound and blend to disrupt granary weevil orientation to odors of wheat grains. The test arena was a steel container (32 cm diameter 9 7 cm height) with two diametrically opposed holes (3 cm diameter) located 3 cm from the side wall.…”

“…Five doses (1, 10, 100, 500, and 1000 lg) of each compound were assessed. Tests lasted 3 h and were carried out in the dark at 25 ± 2°C and 60 ± 5 % r.h. (Germinara et al 2008). There were five replicates of each assay, and insects were only used once.…”

“…In our previous studies, electroantennographic (EAG) tests showed the ability of the peripheral olfactory system of S. granarius males and females to perceive a wide range of cereal volatiles (Germinara et al 2002). In behavioral pitfall bioassays testing different concentrations of individual EAG-active compounds, at specific doses, five compounds (1-butanol, 3-methyl-1-butanol, pentanal, maltol, and vanillin) acted as attractants, while twelve [1-hexanol, butanal, hexanal, heptanal, (E)-2-hexenal, (E,E)-2,4-nonadienal, (E,E)-2,4-decadienal, 2,3-butanedione, 2-pentanone, 2-hexanone, 2-heptanone, and furfural)] acted as repellents suggesting that host finding behavior by the granary weevil more likely depends on the balance of positive and negative stimuli (Germinara et al 2008). Among previously identified repellent compounds, propionic acid and some short-chain aliphatic ketones were found to reduce wheat grain attractiveness to adult granary weevils (Germinara et al 2007(Germinara et al , 2012b.…”