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Diversities of gut endosymbionts in Cowpea beetle on resistant and susceptible cowpea varieties

Olajumoke Alabi: University of Ibadan

<div>Insects harbor endosymbionts that supply essential nutrients and detoxify toxic substances in their food hosts. Resistant populations of Cowpea Beetle (CB) (<em>Callosobruchus maculatus</em> F.) are known to develop overtime on resistant cowpea (<em>Vigna unguiculata</em> [L.] Walp.) varieties due to activities of endosymbionts. However, information on role of gut endosymbionts in CB causing development of resistant populations is limited. Therefore diversities of endosymbionts in CB guts was investigated. Five pairs of newly-emerged adults were introduced into 20g of each of IT96-610, IT81D-994 (resistant varieties) and IfeBrown (susceptible variety). Adult emergence and mean developmental period (days) were assessed. Diversities and counts of bacteria and fungi from guts of F<sub>2</sub> beetles from each of the variety were determined. Sex ratio of 1 male: 3 females was recorded from adults on IT81D-994, while a 1:1 ratio was obtained from the other varieties. Development of beetles was prolonged on IT96-610 (51.0±2.5) and IT81D-994 (51.0±3.0) compared with Ifebrown (39.0±2.0). Bacterial (<em>Bacillus</em> sp., <em>Staphylococcus</em> sp., <em>Micrococcus</em> sp., <em>Streptococcus</em> sp.) and fungal (A<em>spergillus candidus, Penicillium alfredil, Collentrotrichum gloeosporiodes</em>, <em>Aspergillus terreus</em>) strains were isolated from beetles’ guts. Beetles on Ifebrown had the highest bacterial count (12.25x10<sup>4</sup>CFU/mL) and least count was 6.5x10<sup>4</sup>CFU/mL from IT96-610. Highest fungi count, 14.0x10<sup>3</sup>CFU/mL, was from beetles on IT96-610, while the least (6.0x10<sup>3</sup>CFU/mL) was from Ifebrown. IT96-610 and IT81D-994 prolonged development of beetles, while IT81D-994 altered the sex ratio. Use of antibiotics to treat cowpea will destroy endosymbionts in beetles’ guts and consequently reduce damage of seeds in store.</div>