Biological control of the tobacco cutworm Spodoptera litura (Fabricius) (Lepidoptera:Noctuidae) using Sycanus collaris (Fabricius) (Hemiptera: Reduviidae)

Abstract

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.