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D e p a r t m e n t of E n t o m o l o g y , U n i v e r s i t y of Nairobi, P.O. Box 30197, Nairobi a n d The I n t e r n a t i o n a l Centre of Insect Physiology a n d Ecology, P.O. Box 30772, Nairobi, K e n y a ABSTRACTThe tsetse-fly female matures a single oocyte at a time. It ovulates this into the uterus, where it hatches, develops into a full-grown larva, and is later larviposited by the mother. It is only then that the next mature oocyte is ovulated, and the whole sequence is repeated. Thus, in this insect, it is possible to differentiate clearly four processes of egg production: (1) oogenesis, (2) oocyte growth and vitellogenesis, (3) ovulation, and (4) oviposition (in this case, larviposition). Mating is necessary to initiate the process of ovulation, but it is not necessary for the earlier processes. In virgin females, oogenesis, oocyte growth and vitellogenesis takes place normally; but the sequentially matured oocytes are lysed within the egg chambers without being ovulated.

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The relative importance of three factors ‐ mating, nutrition, and crowding ‐ in regulating the reproductive biology of Dysdercus fasciatus Signoret, D. nigrofasciatus Stål and D. cardinalis Gerst. was studied under standard laboratory conditions. Observations on mated and virgin females of these three species of Dysdercus showed that there were no significant differences in pre‐oviposition period and inter‐oviposition period. In D. fasciatus and D. nigrofasciatus there was, further, no significant difference in the rate of oocyte development; but D. cardinalis differed from these two species in that mating had a profound effect on the rate of oocyte development and consequently on the first oviposition. However, in all three species of Dysdercus mating had a significant effect on the number of eggs produced in each batch, the egg batches of mated females being significantly larger than those produced by virgin females. Further, in both D. fasciatus and D. nigrofasciatus virgin females lived longer than mated females but in D. nigrofasciatus mating had no significant effect on adult longevity. Mating activity was drastically reduced in starved adult bugs. But where it occurred under these conditions, mating did not have any effect on the development of the oocytes, even in D. cardinalis. Under starvation conditions, growth proceeded up to the stage where yolk deposition would normally occur, then stopped; the oocytes showed no signs of degeneration or oosorption. Crowding of female adults led to the acceleration of oocyte development and the onset of oviposition in all three species. These findings are discussed in relation to the known field biology of the three Dysdercus species. ÉTUDE COMPARÉE DU DÉVELOPPEMENT DES OVOCYTES CHEZ LES PUNAISES DU COTON DU GENRE DYSDERCUS (PYRRHOCORIDAE) ET LES FACTEURS QUI CONDITIONNENT LA PRODUCTION D'OEUFS. La biologie de la reproduction de 3 espèces de Dysdercus du Kenya a éTÉ étudiée au laboratoire. Des 3 espèces, D. fasciatus Signoret présente Ies périodes les plus courtes de pré‐copulation et de pré‐oviposition. Puisque cette espèce est inféodée à un relativement petit nombre de plantes‐hôtes, qui ont une courte saison de fructification procurant alors une ample source de nourriture, elle tire un avantage maximum de la brièveTÉ de cette période favorable, grâce à la réduction des phases de pré‐copulation et de pré‐oviposition. Par contre D. nigrofasciatus Stål est adapTÉe à un très grand nombre de plantes hôtes et pour elle il n'est pas indispensable d'avoir une très grande capaciTÉ de reproduction. Cela s'applique encore mieux à D. cardinalis Gerst. qui a une plus longue période de pré‐copulation et de pré‐oviposition. Cette espèce préfère les plantes qui sont dispersées sur une grande super***ticie et cela exige une longue période de vol exploratoire avant de s'alimenter et de se reproduire. Chacune de ces 3 espèces s'accouple de façon presque continue, mais les observations faites au laboratoire montrent que l'accouplement n'a aucun effet notable sur la longéviTÉ des adul...