Studies on the distribution pattern of the pine needle gall midge, Thecodiplosis japonensisUchida etInouye (Diptera: Cecidomyiidae) in a pine forest

Abstract

SummaryNumerical changes and distribution patterns of the pine needle gall midge, Thecodiplosis japonensisUchida etInouye, were studied during the period from 1978 to 1979 in a young plantation of Pinus thunbergii in Shiga Prefecture, Japan. The survivorship curve of this species was characterized by a low mortality of larvae in galls and two high mortalities before the formation of galls and during the overwintering period in soil.The within and between‐trees distributions of eggs and larvae in galls were examined by using the regression method. The egg distribution per shoot was aggregative both within and between host plants. The within‐tree variations in numbers of eggs per shoot were related to the differences in the abundance of available needles for oviposition per shoot among the canopy layers. The between‐tree variations reflected the heterogeneous emergence of adult females in the study plot. The degree of aggregation increased from egg to gall stage in both within‐ and between‐tree distributions and the increase was explained by the different mortality of larvae within trees and the inversely density‐dependent mortality between trees.The distribution patterns in the soil habitat stages were examined by the patchness index (). This species showed aggregative distributions in soil stages. There was a correlation in spatial patterns of adult emergence between the successive generations.The distribution properties of this species were discussed in connection with the population dynamics and the availability of host plants in the study plot.