SPERM SIZE OR NUMBERS - EFFECTS OF NUTRITIONAL STRESS UPON EUPYRENE AND APYRENE SPERM PRODUCTION STRATEGIES IN THE MOTH PLODIA-INTERPUNCTELLA (LEPIDOPTERA, PYRALIDAE)

1. Sperm numbers are important for fertilization and sperm competition success but the importance of sperm size is not known. 2. We forced m ales of a meal moth (Plodia interpunctella) to develop on a low-protei n diet with intense competition for food and compared their sperm size s and numbers with sperm produced by males developing on a normal diet . 3. We find that males suffering resource restrictions for spermatoge nesis reduce sperm numbers but not sperm sizes for both the fertile 'e upyrene' and non-fertile 'apyrene' sperm types. Under a restrictive la rval diet, males do not alter the relative proportion of apyrene to eu pyrene sperm produced from a 9:1 ratio. 4. We conclude that apyrene sp erm play a critical role in the ejaculate and that both sperm sizes ar e constrained about narrow optima. The results suggest that males woul d suffer more drastic fitness losses for their ejaculate if they varie d sperm sizes rather than numbers, as predicted by recent ESS sperm co mpetition models.