Using the mosquito Aedes aegypti in a novel olfactometer that measures movement towards and away from a stimulus, we could not confirm that 'deet' is a repellent of mosquitoes. In the absence of a host, deet was an attractant and in the presence of a host, it was an inhibitor of attraction. This inhibition occurred in the gaseous phase and was therefore not the result of the physical properties of deet. We determined that L-lactic acid, a component of human sweat that is an attractant to mosquitoes, is the target of this inhibition, implying that lactic acid may be a bottleneck in the behavioural cascade preceding blood-sucking.
The olfactory ability of the convergent lady beetle, Hippodamia convergens Gué rin-Mé neville, was investigated using an 8-arm airßow olfactometer. Lady beetles tested were normal or had their antennae, antennal tips, or maxillary palps amputated. Normal beetles and those with their maxillary palps removed were highly attracted by the odor of radish leaves infested with green peach aphids, Myzus persicae (Sulzer). Beetles with their antennae or antennal tips removed were not attracted. In addition, the normal lady beetles were signiÞcantly attracted to clean radish leaves. These results indicate that H. convergens can perceive olfactory stimuli released by their prey and their preyÕs host plant (or a combination of the two) and that the beetlesÕ olfactory receptors are located principally on the tips of their antennae. Also as part of this study, the antennal sensilla of male and female convergent lady beetles were examined using scanning electron microscopy. The sensilla were counted, the majority of which were located on the terminal segment, and 4 morphological classes were identiÞed: chetiform, Bö hm, basiconic, and trichoid. Chetiform sensilla were observed on all 11 antennal segments, while the Bö hm sensilla were located only on the Þrst two segments. The basiconic and trichoid sensilla were located exclusively on the terminal two segments. The most abundant sensilla on the terminal segment, trichoid sensilla, were suggested to function in olfaction.
We exposed larval and adult Hippodamia convergens (Guerin-Meneville),convergent lady beetle, to Myzus persicae (Sulzer), green peach aphid, reared on potatoes expressing &-endotoxinof Bacillus thuringiensis tenebrionis. Because the toxin may be ingested by the aphid, the beetle may in tum be exposed to the toxin. However, we measured no statisticallysignificanteffect on survival,aphid consumption, development, or reproduction in beetles.
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