Effects of Nosema Infection on Ovipositional Preference and Larval Performance of Plutella xylostella (L.) (Lepidoptera: Plutellidae), on Some Brassica Plants

AbstractBiological control, using pathogenic microsporidia, may have the potential to be an alternative to chemical control against the diamondback moth (DBM), Plutella xylostella (Lepidoptera: Plutellidae). The microsporidium, Nosema bombycis (NB), is one of many disease agents that can be used in the Integrated Pest Management (IPM) of DBM. Nosema bombycis affected DBM fecundity negatively and may affect its preference to lay eggs on particular host plant species. To investigate this, infection was performed on second instar larvae of DBM and the emerged adults were released into cages in greenhouse. A choice experiment with whole plants was conducted with four selected hosts: rape leaves, Brassica juncea, green mustard, B. Chinese, cabbage, B. Oleracea and pak choi, B. Rapa to examine adult oviposition preference for both untreated and N. Bombycis-infected DBM. P. xylostella performance (larvae hatched, pupae developed, adults emerged and developmental time for each stage) parameters were also conducted using mean values for each host plant and the results showed that it varied between plants. For untreated DBM, rape plants were the most preferred for oviposition, and more eggs were laid by DBM on rape than either green mustard or pak choi while oviposition was lowest on cabbage. However, the infected DBM exhibited no significant different in egg laying preference between rape, green mustard and pak choi with low number of egg laid irrespective of host plants. Interestingly, Normal and Nosema-infected DBM adults showed an unattractive egg laying behaviour to cabbage