ABSTRACT
Contact kairomones are essential for host-acceptance behaviour by female parasitoids. In the solitary endoparasitoid wasp, Diadromus pulchellus, this behaviour depends mainly on compound(s) in the cocoon of their host, Acrolepiopsis assectella pupae. Extracts of empty cocoons and polypeptides extracted from cocoons were tested in acceptance behaviour assays using cotton fibre lures bearing extracts. Extractions with solvents of increasing polarity indicated that the active compounds were polar, while SDS-PAGE showed that four glycopolypeptides contained enough information to trigger host-acceptance behaviour in female wasps. This kairomonal activity was found to be due to the protein moieties, and was independent of any glycosylation. These four glycopolypeptides might be two variants of two soluble sericin-like polypeptides differing in their degree of glycosylation.
ABSTRACT
A comparison of the walking locomotory reactions of flightless and flight formCallosobruchus maculatus males when subjected to an air current scented with female sex pheromone was undertaken in a tubular olfactometer. The pheromone was delivered to the males either as short pulses or as a continuous flow. To analyze the males' reactions, three behavioral sequences were defined (sequence 1: male sensitivity/arousal; sequence 2: male reactivity; sequence 3; male progression and source location). Although flightless and flight form males were sensitive and reactive in all experiments, their locomotory displacement differed depending on the stimulus conditions. The flightless form males' response remained roughly the same whatever the stimulus conditions (i.e., they always reached the pheromone source). In contrast, the flight form males displayed a markedly reduced response when subjected to a continuous stimulation, indicating that intermittent on-off pheromone stimulation is required in order to sustain their upwind walking progress. This effect could be the result of sensory adaptation and/or habituation in the central nervous system of the flight form, requiring a flickering signal that is unnecessary for the flightless one.
ABSTRACT
Survival ofAcanthoscelides obtectus larvae depends on the ability of the first instar to pierce the seed coat ofPhaseolus vulgaris, which represents a critical sequence because of physical characteristics and toxicity. We have investigated the influence of seed surface quality on larval boring behavior by the usual method of surface washing with different solvents, or by removing the testa, or by coating the testa with a polymer spray. Observations were made on isolated larvae in no-choice and dual-choice bioassays. In the no-choice situation, larval penetration was reduced after seed coats were soaked with chloroform, whereas water, diethyl ether, or methanol had no significant effect. The ratio of boring attempts to successful penetrations was increased on seeds washed with chloroform. In the dual-choice situation, larvae avoided artificially coated seeds and preferred untreated seeds over those washed with chloroform or methanol. These results indicate that boring stimulants exist on the seed coat and that they are removed by chloroform and methanol or made inaccessible by artificial coating. The high mortality of first instars on seeds washed with these two solvents is attributed to a lack of chemicals necessary to initiate and sustain boring behavior, causing larval stress, possibly due to prolonged locomotory activity and starvation. Thus, seed coat quality may influence the population dynamics ofA. obtectus.
