Effects of the gregariousness of larvae in galls on the reproductive success of the pine needle gall midge, Thecodiplosis japonensis Uchida et Inouye (Dipt., Cecidomyiidae)

Abstract The effects of the gregariousness of larvae of the pine needle gall midge, Thecodiplosis japonensis Uchida et Inouye (Dipt., Cecidomyiidae), on the reproductive success of the midge were examined by field observations and laboratory experiments. The gregariousness of larvae in a gall did not cause the death of larvae in the gall, and the number of emerged adults per gall was expected to increase with the number of larvae per gall. Gregariousness decreased the size of larvae in galls. The decline in the larval size did not cause a simple decline in the number of eggs deposited per female. Females that emerged from medium size larvae deposited many more eggs than those from large and small larvae. The calculated number of eggs deposited per gall increased with an increase in the number of larvae per gall from one to five, but not when the number of larvae per gall was more than six. A simple model showed that if a female deposited about 10 eggs per egg cluster the number of eggs deposited by her daughters in the next generation would be maximum. The oviposition pattern and the gregariousness of larvae in galls in the field probably offer the midge the maximum reproductive success.