Theoretical models predict that brood guarding may evolve in situations where eggs are costly to produce or when handling times are long. This study reveals that females of the secondary hyperparasitoid Trichomalopsis apanteloctena guarded cocoon broods of Cotesia kariyai, a gregarious endoparasitoid. Hyperparasitoid females also monopolized host resources and protected their offspring by driving away other conspecific hyperparasitoid females. The females exhibited antagonistic behavior towards competitors through threatening body postures, biting and chasing. Using a video camera to determine how long a hyperparasitoid female attended and parasitized cocoons within a single host brood, it was found that after about 4 days, cocoon guarding behavior became much less apparent. Moreover, more than 90% of hosts were typically parasitized by a hyperparasitoid female over the course of 4 days after she commenced brood guarding. Observations of egg production during a female's lifetime revealed a physiological interval rhythm that typically lasted 3-4 days, which correlates almost exactly with the period during which the cocoons were guarded. To confirm the giving-up time for a host cocoon brood, hyperparasitoid females were given access to 24 h-old cocoon clusters, each containing 60-100 individual cocoons. Ninety percent of the females remained on cocoons for approximately 72 h. Furthermore, twenty-five percent of wasps continued attending and presumably guarding host cocoon broods for more than 138 h after the female first attended the brood. C. kariyai larvae pupate within a few hours of egression from their host and emerge as adults about 5 days (120 h) later. Therefore, many hyperparasitoid females continued to guard older host cocoons of greatly reduced quality as a resource for their progeny and some even after eclosion of the primary parasitoid. Late-brood guarding enabled a hyperparasitoid female to protect her own progeny from other hyperparasitoid females that readily attacked and killed them when she was removed. Our study thus reveals that extended guarding behavior is an adaptive mechanism that probably plays an important role in the survival of the original brood.
When insect herbivores develop over many generations on the same plant species, their descendants may evolve physiological adaptations that enable them to develop more successfully on that plant species than naïve conspecifics. Here, we compared development of wild and lab-reared caterpillars of the cabbage moth, Mamestra brassicae, on a cultivar of cabbage Brassica oleracea (cv. Cyrus) and on a wild plant species, sorrel, Rumex acetosa, on which the wild strain had been collected and reared for two earlier consecutive generations. The lab strain had been reared on the same cabbage cultivar for more than 20 years representing > 200 generations. Survival to adult did not vary with strain or plant species. Both strains, however, developed significantly faster when reared on R. acetosa than B. oleracea. Pupae from the field strain were larger when reared on B. oleracea than on R. acetosa, whereas the identity of the plant species did not matter for the lab strain. Our results show that long-term rearing history on cabbage had little or no effect on M. brassicae performance, suggesting that some generalist herbivores can readily exploit novel plants that may be chemically very different from those on which they have long been intimately associated., Jeffrey A. Harvey, Eke Hengeveld, Miriama Malcicka., and Obsahuje bibliografii