On Competition among Larvae in Experimental Population of a Leaf Mining Fly, Phytomyza ranunculi SCHARANK : Diptera : Agromyzidae

Abstract

The present study was carried out to clarify the competition among larvae of a leaf mining fly, Phytomyza ranunculi, in the leaf of a host plant, Ranunculus asialicus LINNAENUS.The larval mortality in the leaf and the percentage of larvae that moved out from a leaf to a petiole increased with increase of the number of hatching larvae per cm² of the leaf area.It was found that most of the dead larvae in a leaf were young instars. The mortality of young larvae was high when the difference in development among individuals in the same leaf was large because the survival of the late-developed larvae was much lowered due to deterioration of the leaves, mainly caused by the feeding activity of the early developed larvae. In many cases, the larvae which moved out to the petioles or branches tended to be smaller than those that emerged from leaves. Also, the early emerged pupae were larger in size than the late emerged ones. The maximum density of mature larvae emerged from a leaf was about 2 per cm² of leaf area when eggs were laid only for two days but it was much lower when the oviposition period extended over five days.