Reproductive pattern and population dynamics of aphids having sterile soldier caste.

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Pattern of production of sterile soldiers and population dynamics of two species of bamboo aphids, pseudoregma koshunensis and P.bambucicola, having sterile soldier caste, were studied in Okinawa and Kagoshima. Major results are as follows :(1) Virginoparous females of P.koshunensis first laid normal (to-be-reproductive) larvae and secondly soldier-type larvae. This pattern is quite different from other eusocial insects, all of which produce workers first and to-be-reproductives secondly. (2) In Kagoshima, the number of P.bambucicola individuals began to increase from August, reached its peak in October, then decreased and became nearly zero in July. The soldier ratio was highest in October and November (ca. 20%) and decreased to 10% in March and nearly 0% during period from May to July. On the other hand, in Okinawa, the number began to increase from June, reached the peak at July or August, then decreased. The number was very low in December and became nearly zero during February and March. The soldier ratio was highest in autumn but even in autumn it was far lower than Kagoshima (usually less than 5%). (3) A reason of different population trends between Kagoshima and Okinawa might be difference of badding season of bamboos in the two areas. (4) In Okinawan populations morphological difference between normal and soldier type larvae was not clear as compared with clear difference in Kagoshima. This fact and difference in soldier ratio suggested existence of some genetic differences between the two strains.