WHO EATS WHOM - COMPLEX INTERACTIONS BETWEEN AN EGG PARASITOID AND ITS CANNIBALISTIC HOST

Interactions between an egg parasitoid (Telenomus sp., Hym., Scelionidae) and its cannibalistic host (Spilostethus pandurus, Het., Lygaeidae) were studied in the laboratory. Parasitoids oviposit in newly laid host eggs which are either fertile or infertile. Host larvae, which hatch before parasitoids, are cannibalistic and attack sibling eggs. These are of three kinds, viz. unparasitized fertile, unparasitized infertile, and parasitized. Preference tests show that both ovipositing parasitoids and feeding host larvae attack all kinds of eggs but at widely different rates. Host egg batches of different sizes were arranged and subjected to attack by one parasitoid female to study interactions between batch size, parasitism and cannibalism. As a result of reciprocal predation by "hosts" parasitoids gain increasing returns from each fertile host egg attacked in a batch. They also prefer fertile over infertile host eggs. Hatched host larvae gain increased survival by feeding on sibling eggs. Infertile eggs, which are preferred, thus contribute to their fitness. Parasitoid attacks lead to strong changes in the ratio of infertile to fertile eggs in differently sized egg batches. Thus the fitness contribution of infertile eggs to hatched siblings will change in response to batch size and parasitoid attack.