The effect of different instars of black bean aphid, Aphis fabae (Hem., Aphididae) on fitness obtained in sexual strain of Lysiphlebus fabarum (Hym., Braconidae)

Parasitoid wasps usually encounter hosts of different ages or sizes and they select the most suitable hosts to maximize their reproductive fitness. In this study, a sexual population of Lysiphlebus fabarum was reared on different instars of the black bean aphid, Aphis fabae Scopoli, to evaluate some biological components. The results showed that pre-adult development times were decreased with increasing the host body size (from first to third instars), but the longest period was observed in the fourth instar. There was no significant difference in the rate of parasitism of the different treatments, while sex ratios in wasps reared in first and third instars were the most. The largest wasps were observed in wasps reared in second instar as well as, these wasps had a high egg load and egg size. Moreover, a survey on lifespan of parasitoids reared in different host instars showed that the maximum longevity was observed in the wasps reared in second and fourth nymphal instar, in the presence of host aphids. Totally, the greatest fitness was achieved when the wasps were reared in second nymphal instar of aphids, although the wasps reared in other instars obtained some biological components.