Abstract
Isotima javensis is a solitary ecto parasitoid of the sugarcane top borer, S. exceptalis. It attacks the prepupal stage and deposits an egg either on the prepupa or near its vicinity. The extent of parasitisation was observed 2.12%, 4.28%, 7.14%, 5.88% and 5.23 % in I, II, III, IV and V broods of top borer, respectively. The contribution of mortality of pupae of the top borer by parasitisation is high in III and IV broods (Aug-Oct), the time when the brood infestation remains generally very high. The maximum female ratio (59.72%) was observed in III brood of parasitisation followed by 55.20 % in IV brood. In I and II broods, however more or less equal number of males and females can be observed in the field. Equality in the sex ratio at this time ensures fertilisation of almost all the females for retaining the vigour and vitality of the species. The absence of unfertilized parasites naturally removes the chances of parthenogenetic reproduction and thus the number of females gradually rises in the succeeding season. It is concluded that there are several attributes of parasitoid i.e. specific parasite of top borer; its life cycle is much shorter than its host; active throughout the period of activity of the host and even it hibernates under north Indian conditions which make it a good biocontrol agent. It is suggested that parasitoid may be exploited in biological control programme, more detailed study is required for mass multiplication in the laboratory on an alternate host, release technique and survival in the sugarcane field.
Sugarcane top borer, Scirpophaga excerptalis F. is a major pest of sugarcane in almost all the important cane growing areas of India (Gupta 1959 and Sithanantham 2013). The pest passes through 5 to 7 broods in a year under north Indian conditions (Kalra and David, 1967). The borer spends major portion of the life-cycle within the plant tissues, the short period passed outside is either as adult or in the egg stage. The young caterpillars enter the leaf mid-ribs within a few hours of their hatching from the eggs, and after that the pest remains hidden inside the plant tissue till its emergence as moths. However, immediately before pupation, the grownup caterpillar cuts an exit hole in one of the top internodes for the emergence of moth at later stage. This exit hole renders the grown up caterpillar or the newly formed pupa vulnerable to parasitisation by Isotima javensis (Kalra and David, 1967). Top borer larva/prepupa has been recorded parasitising by parasitoids, I. javensis, Rhaconotus scirpophagae, Stenobracon niecevillei/ deesae, Elasmus zehntneri (Gupta, 1958, Rahman, 1976 and Tanwar and Varma, 1997).
Keywords
Sugercane, Top Borer, Parasititation
Refbacks
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