M Sc

Salad cucumber (Cucumis sativus L.) is among the most popular vegetables
grown in polyhouses across Kerala, which has been gaining significance in recent
years. However, the warm, humid conditions, abundance of food and the relatively
low presence of natural enemies encourage build up of arthropod pests in polyhouse
cultivation. Among these, the tobacco cutworm Spodoptera litura
(Fab.)
(Lepidoptera: Noctuidae) is one of the destructive pest. Management of the tobacco
cutworm using insecticide based management strategies is not advisable as cucumber
fruit is consumed in raw form. Biocontrol could be a more ecologically sound and
economically feasible alternative. The reduviid bug, Sycanus collaris (Fab.)
(Hemiptera: Reduviidae) is one such potential candidate for biocontrol of S. litura in
polyhouses. However, S. collaris remains to be evaluated as a biocontrol agent under
Kerala conditions. Hence a study was conducted to investigate the biology, functional
response and prey stage preference of the reduviid predator S. collaris as well as to
evaluate its potential for the management of S. litura on cucumber under polyhouse
cultivation.
Biology of S. collaris was studied on larvae of Galleria mellonella. Eggs were
hatched after a mean incubation period of 13.21 days. Development of nymphs,
normally with five instars, with a mean duration of 12.55, 9.12, 8.88, 10.95 and 15.93
days respectively. After the pre oviposition period of 12.60 days, egg laying
continued for 51.86 days. Females died in 13.43 days after laying last batch of eggs.
Average fecundity of the bug was 451.56 eggs. Mean longevity of 78.95 days was
longer for females than 66.29 days for adult males.
Functional response of fifth instar nymphs of S. collaris on third instar larvae
of S. litura at different prey densities of 1, 2, 4, 8 and 16 larvae/bug was assessed in
laboratory. Nymphs of S. collaris killed up to 5.50 larvae in 24 h at a prey density of
16 larvae per bug. Logistic regression analysis revealed a type II curvilinear
functional response with an attack rate of 0.0198 h -1 while the handling time was
between 0 to 0.460 h.The prey stage preference of the fifth instar nymphs of S. collaris on S. litura
was studied by offering all the five different larval instars larval instars in equal
proportions of 2:2:2:2:2 ratio. The predator showed marked preference towards first,
second and third instar larvae of S. litura larvae over fifth instar larvae. The predator
also showed significantly higher preference to third instar S. litura larvae as compared
to fourth instar larvae.
Biocontrol potential of S. collaris against tobacco caterpillar, S. litura on salad
cucumber in polyhouse conditions was evaluated on KPCH 1 variety of cucumber.
The plot in which predator was released recorded significantly lower number of S.
litura compared to untreated control. The population of S. litura declined by 63.4 and
89.4 per cent, respectively on the first and third day after release of the predator and
no larvae were observed on the five days after bug release. However, the larval
population of five per plant showed no reduction after five days, in control plots. The
mean yield per plant in which predator was released @ 100 nymphs/50 m 2 recorded
significantly higher yield than control plot.
The study demonstrated that the reduviid predator S. collaris can be used for
inoculative release for the management of S. litura in protected cultivation.