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[Temperature dependence of the electrical activity of wasp cardiac function].

Changes in the temporal structure and amplitude of electrical fluctuations connected with the heart function were revealed by the electrophysiological method. In the range of optimum temperatures, high- and low-amplitude impulses are predominantly generated. Their amplitudes differ approximately by a factor of three. Hypo- and hyperthermia stimulate pauses in heart function. Their duration increases with the unfavorable effect of temperature. During the activation of heart function, high-amplitude fluctuations are predominantly generated. In cold torpor, all forms of electric activity stop, whereas in the active state they are resumed.

Animals↗
PubMed1997

Female size affects provisioning and sex allocation in a digger wasp

Investment ratios in field populations of the European beewolf, Philanthus triangulum F. (Hymenoptera, Sphecidae), are strongly biased towards males. Possible explanations are conditional sex allocation and/or constraints on provisioning females: daughters need at least three prey items (honey bees), whereas sons need only one to develop and reproduce. If small females are not able to procure these three bees quickly enough they might have to produce sons instead. Larger females had a higher proportion of successful hunting flights, carried heavier loads, and could fly continuously with a load for longer than small females. They brought in more and heavier bees but needed less time for a single hunting trip. An estimate of the sex allocation of the food bees, based on the timing pattern of successful hunting trips, suggested that female size is positively correlated with the proportion of daughters produced. However, this effect explains only a small part of the overall variation in investment ratio.

Journal Article↗
PubMed1998

The effect of complete versus incomplete information on odour discrimination in a parasitic wasp.

We studied the function of learning in the parasitoid Leptopilina heterotoma by looking at discrimination of odour stimuli used in foraging for a host. To optimize the rate of encounters with hosts, these parasitoids are expected to assess the extent to which variation in host-substrate odours is reliably associated with variation in the presence of hosts, that is, substrate profitability. Where the association is reliable, parasitoids should attend to variation in odours and discriminate between them; where it is not, they should ignore it. We hypothesized that foraging decisions are based on the completeness of information the animal has about differences in substrate profitabilities. Our laboratory studies showed that discrimination and non-discrimination of odour stimuli are dynamic behavioural decisions that can be related to the degree of substrate variation and to an animal's informational state. In wind-tunnel studies, females learned to discriminate between odours from substrates that were qualitatively different, for example, between odours from apple and pear substrates or between yeast substrates with different C6 compounds added. They did not discriminate when differences were small (e.g. between odours from two apple varieties or between yeast patches with different concentrations of ethyl acetate), unless unrewarding experiences provided evidence of the absence of hosts in one of the substrates. Hence, we suggest that non-discrimination between odour stimuli in L. heterotoma is not a lack of ability to discriminate but a functional decision by the parasitoid. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.

Journal Article↗