TEMPERATURE DEPENDENT DEVELOPMENT RATES OF PARASITOID, HABROBRACON HEBETOR, DIRECTLY FED ON BACILLUS THURINGIENSIS VAR. KURSTAKI

Abstract

The interaction of temperature and directly ingested Bacillus thuringiensis (Bt), on the developmental rates of the parasitoid Habrobracon hebetor progeny was investigated using Corcyra cephalonica 4th instar larvae as host. Development rates increased with temperature rise. Regression analysis revealed highly significant (p <.01) good fit of the equation for incubation, larval and total lifecycle period, while significant (p <.05) for larval period in untreated diet fed H. hebetor, However, under the influence of Bt- honey diet, larval period (p >.05) was not a good fit of the equation. Although r- values were overall lower and regression showed no significant fit of the equation for larval periods, significantly higher development rate was observed towards higher temperatures. However, rates during pupal period and total lifecycle showed highly significant (p <.01) good fit of the equation. Significant interactions between Bt and temperature were observed during larval (F3,72= 45.443, p <.001) and pupal periods (F3,72= 3.932, p <.05), however, no such significant interaction occurred during incubation period (F3,72= 1.643, p= .187). Mean developmental rates during total life cycle also showed significant interaction between the factors, F3,72= 4.684, p <.01. Temperature was way more influential in all stages, as a factor (p < .001), than Bt. This study emphasizes the importance of temperature as an ecofactor during combined biological control. Interaction between higher temperatures and Bt, within the tolerance limit, may actually be beneficial through faster development during larval stage; although the same cannot be said of the other parameters of its life history.