MSc

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.