INSECT BIODIVERSITY AND ASSESSMENT OF POST-HARVEST GRAIN LOSSES IN STORED COWPEA (Vigna aunguiculata L.)

Abstract

Insect pests cause huge economic losses to stored grain cereals and pulses in tropical and subtropical areas around the globe. The level of damage and losses caused by different insect pests varies depending upon the infesting species, type of food materials, duration of storage and structures. The information about the diversity of infesting species, their dispersal and abundance are key for devising effective pest management techniques against storage insect pests. The present study aimed to collect information on the distribution, relative abundance and biodiversity of major insect pests of stored cowpeas in Dera Ismail Khan (Khyber Pakhtunkhwa) and its adjoining Punjab province areas of Pakistan. The areas selected for biodiversity studies were Paniala, Mankera, Bhakkar, Paharpur, Kulachi, Ramak, Dera Ismail Khan, Darya Khan, Notak and Behal. A vast survey of godowns was conducted to find out the population dynamics of insect pests of stored cowpeas and to explore the % grains damage and weight losses in the mentioned areas. For the collection of samples, a spear sampler was used to collect 500-gram samples from the top, middle and bottom portions of the bags. Samples were preserved in plastic containers and after 30 days, were sieved out with the help of a 2mm mesh sieve to remove different types of dead and alive insects. A total of five species representing two distinct orders i.e., Coleoptera and Lepidoptera. Coleopterans are Callosobruchus maculatus, Tribolium castaneum, Oryzaephilus surinamensis, Trogoderma granarium belonged to four families including Chrysomelidae, Tenebrionidae, Silvanidae, Dermestidae and Lepidopteron are Sitotroga cerealella belonging to family Gelechidae. The most abundant species among all the recorded insect pests of cowpea was C. maculatus (53.60%) followed by T. castaneum (18.60%), S. cerealella (16.97%), O. surinamensis (6.49%) and T. granarium (04.34%). The maximum infestation (26.98%) and weight loss (28.91%) of cowpea was recorded in Darya Khan followed by Dera Ismail Khan (22.70% and 26.33%), whereas; minimum % infestation and weight losses were recorded in Bhakkar (16.91% and 17.14%) area showing significant differences between the surveyed areas. The C. maculatus is the most abundant specie of the stored cowpea grains in the surveyed areas and needs management tactics to minimize the post-harvest grains losses. The population of C. maculatus starts to build up during the month of March (23.30⁰C and 56.25% RH) and reaches at peak in May (35.32⁰C and 68.88% RH). Special measures should be taken during these months to minimize the infestation and losses caused by C. maculatus.