PUB - Publikationen an der Universität Bielefeld

The egg distribution of the monophagous noctuid moth Abrostola asclepiadis was related to the characteristics of host plant patches and individual plant shoots. Both the density and size of egg batches were greater in small, shaded host plant patches than in large, sun-exposed ones, and egg batches were larger on short host plants than on tall ones. We examined the consequences of this egglaying 'preference' on offspring performance. In the field, there was no difference in either egg or larval mortality between patches differing in degree of sun exposure or size. Nor did mortality differ between batches on small plants and those on taller plants. Furthermore, neither larval growth rate nor pupal size showed any relation to egg-laying 'preferences'. Larvae fed foliage from small, shaded plants ended up smaller than larvae fed foliage from large, sun-exposed plants, but the development rates of the two groups were similar. There was no difference in weight or rate of development between larvae fed foliage from large, sun- exposed plants and those fed foliage from large, shaded plants. Hence, neither the 'preference' for certain patches nor that for certain host plant individuals seemed to be related to larval performance. Reasons for the tendency to deposit large egg batches on small plants remain obscure. However, there is an alternative explanation as to why more eggs were laid in shaded patches, namely that these patches are less subjected to drought, and host plant wilting is therefore less common. An 18-yr record shows that droughts intermittently cause severe drying out of plants in sun-exposed, rocky positions.