The relationship between conspecific superparasitism and the outcome of in vitro contests staged between different larval instars of the solitary endoparasitoid Venturia canescens |
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Authors: | G C Marris Julia Casperd |
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Institution: | (1) Central Science Laboratory, London Road, Slough, SL3 7HJ, Berkshire, UK, GB;(2) Department of Psychology, University of Liverpool, PO Box 147, Liverpool L69 3BX, UK, GB |
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Abstract: | When endoparasitoid wasps oviposit into hosts which have already been parasitized (= superparasitism), this results in potentially
lethal interlarval competition. For solitary species, the decision to lay additional eggs should therefore be based on the
probability of superparasite survival in any superparasitized host. In this study, in vitro contests staged between three larval instars of Venturia canescens Grav. (Hymenoptera: Ichneumonidae) reveal that the age difference between competitors affects the outcome of interlarval
competition. Three parameters were used to assess parasitoid performance: the number of fights initiated, the number of bites
inflicted, and the duration of each bite. When fighting takes place between two first instars, then both competitors were
found to be evenly matched. However, at greater age differences, first-instar competitors appeared to win more fights than
their larger second instar rivals. The advantage shown by younger competitors is most pronounced in contests staged between
first and third instar larvae. These findings are consistent with the increasingly high levels of conspecific superparasitism
shown by V. canescens in the first 5 days after initial host attack, suggesting that this parasitoid can deploy her use of deliberate superparasitism
in an adaptive way.
Received: 13 December 1995/Accepted after revision: 5 March 1996 |
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Keywords: | Solitary endoparasitoid Interlarval competition Conspecific superparasitism |
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