Biodiversity and bionomics of predatory coccinellids in vegetable crops

Abstract

The role of biocontrol in keeping the natural balance of the ecosystem is universally accepted. However, the use of insecticides, interventions by man viz. cropping patterns, other methods of control, resistant varieties etc. may cause changes in natural enemy population. No information is available on the number and suppressive potential of predatory coccinellids and their effect on pest population and the present study is intended to meet the aforesaid desideratum. In the present investigation the detailed biology of the coccinellid predators prevalent in the vegetable crops like cowpea, bhendi, brinjal, pumpkin and bittergourd was studied under laboratory condition. Fecundity, predatory potential and feeding preference of these predators were also ascertained. Seasonal fluctuation of aphid and coccinellid predators was studied from June 2001 to May 2002 in cowpea, bhendi, pumpkin, brinjal and bittergourd. Coccinellids like Coccinella transversalis Fab. , Cheilomenes sexmaculata, (Fab.) Brumoides suturalis(Fab.) and Jouravia soror Weise were persistent in the vegetable ecosystem. Biological data indicated higher feeding potential of C. transversalis (213.5 ± 4.710 aphids) and C. sexmaculata (226.2 ± 2.77 aphids), which shows that they can effectively control A. craccivora. Higher fecundity of C. transversalis (421. 8 ± 4.983 eggs) account for the successful establishment of these predators in the field: Feeding preference study was conducted by no choice test and multiple choice test. CoccinelIids ate only aphids in both the situations. The population of aphids and coccinellids vary widely in different crops.ln cowpea, aphid and coccincllid population. were present throught the course of study. Maximum aphid population (221.5 and 22) was seen on the first fortnight of January in cowpea and bittergourd respectively, whereas the maximum coccinellid population was noticed during the second fortnight of January (1.2) in the former and first fortnight of February (0.4) in the latter. In pumpkin and brinjal, peak population of aphids (29.8, 22.4) and coccinellids (0.5,0.2) were observed on the second fortnight of January and in bhendi on the first fortnight of February (aphids 32.5, coccinellids 0.5) Correlation studies between aphid and coccinellid

coccinellid population with weather factors was also studied. Rainfall and temperature was having negative correlation with aphid population. Coccinellid population did not show any significant relation with weather factors except in cowpea. Influence of relative humidity on aphids and coccinellids vary widely in all the five crops. The inconsistency may be due to numerous factors interacting among the components of the biotic systems and their interaction with numerous abiotic factors. For consistent conclusions these correlation studies may have to be extended over a number of seasons.