The distribution pattern and seasonal incidence of spider (Araneae: Araneidae) prevalence in the onion ecosystem of West Bengal’s red lateritic zone

Abstract

Background: One of the best methods to reduce the usage of chemical pesticides and insect pests is biological control using spiders. Natural enemies, such as predators, parasitoids, and pathogens, play a crucial role to minimize the use of chemical pesticides and insect pest complexes in onion ecosystem. The experiment was conducted in order to know the seasonal incidence and distribution pattern of Spider in onion ecosystem at Sriniketan, West Bengal, India during rabi season 2021-22. Healthy seedlings of onion were transplated on the experimental field. To check the seasonal incidence and dispersion of spider, the field was inspected on a weekly basis. Different indices of dispersion i.e mean, variance, variance-mean ratio, dispersion parameter ‘K’, David and Moore’s index, Lexis Index, Charlier coefficient, Index of dispersion, Lloyd mean crowding index were calculated by using of pooled data and checked the distribution pattern of the predatory agent spider. Results: When insect pests appeared, species of spider were discovered on the crop to reduce the pest population in the agroecosystem. Spiders were observed at different temperature, relative humidity, growth period of onion throught the cropping season. Highest Spider population was found during the 4th week of February, about 3.14 spiders per plant. The distribution of spider during the crop-growing season was clumped, infectious, and aggregative, as shown by various dispersion indices. The majority of the standard weeks' computed K values, however, were found to marginally depart from the negative binomial aggregative kind of dispersion. Conclusion: Our study was able to characterize the population, spatial distribution of spiders in onion ecosystem and develop a comprehensive sampling plan for their population assessment. Future studies can validate this sampling scheme for major onion growing areas in the red lateritic zone of West Bengal and examine the spatial distribution of an additional natural enemy i.e. spider, to improve pest management programs for major insect pest of onion.