Comparing the Rations of Leaf-acceptance Prior to Egg-Laying among several species of Leaf-mining Moths upon Quercus sp pl (Lepidoptera: Gracillariidae, Tischeriidae)

Abstract

Optimal selection among host-units intended to support eggs-deposits is of paramount importance for those insects species with larval stage concealed within one and unique host-unit, such as leaf for leaf-miners. Selection is expected to be particularly severe (leaf acceptance ratio low) when insects specialise upon tough materials with efficient chemical defence, as is the case with oaks leaves. Yet, beyond egg-laying mothers selectivity, a complementary strategy to cope with such leaves opposing substantial deterrents, would consist in adopting more thoroughly a regime which escapes partially these defences such as sap-feeding instead of whole-tissue feeding. Then, mining species which tend to increase the sap contribution of their larval regime might perhaps, hypothetically, relax somewhat the selective exigency of mothers prior to egg-laying. This hypothesis was tested by comparing the leaf-acceptance ratio of Cameraria (larva more consistently sap-feeding) to other mining moth species (becoming more quickly tissue-feeding). Results conform fairly well to the proposed hypothesis but uncertainty remains as for the proper effect of leaves chemical variations among oak species, since we had not the possibility of making more relevant comparisons with mining species occurring on a same oak species. Regarding those results, this work is thus preliminary and in fact, addresses at first a methodological aspect of the question: the implementation of a new procedure allowing convenient quantitative inferences of both leaf-acceptance ratio and clutch-size, on the basis of easily recorded field-data collected a posteriori.