Efficacy of Locally Produced Papain Enzyme for the Production of Protein Bait for Bactrocera Invadens (Diptera: Tephritidae) Control in Ghana

Abstract

Autolysed brewery yeast waste is currently being used as cost effective protein bait for Bactrocera invadens control the world over to replace commercial protein hydrolysate bait formulations. However, significant reduction in production cost can be achieved when all the production materials are from local sources. This experiment was aimed at assessing the efficacy of locally produced papain extracted from ―Red lady‖ pawpaw fruit latex and skin peel to be used for protein bait production. Aqueous two-phase extraction of papain from pawpaw fruit latex with 15 % (NH4)2SO4 - 8 % PEG recovered 64.72 ± 2.08 % papain into the supernatant with 7.33 % proteolytic activity yield and a fold purification of 58.11 ± 1.67. Proteolytic activity and protein concentration measured for the aqueous two-phase extracts of pawpaw skin peel were significantly higher (p= 0.00) than crude extracts of skin peel. However, the aqueous two phase extraction of papain from skin peel needs to be optimised further since SDS-PAGE showed no visible bands in the different phase extracts. Gamma irradiation at 10 KGy increased the proteolytic activity of crude papain by 21.69 % of the non-irradiated papain and subsequently increased the specific activity by 18.51% but the protein concentration was not affected. Protein baits prepared with crude papain extracted from the pawpaw fruit latex and skin peels were evaluated in laboratory bioassays with wild flies reared from field collected infested mangoes. The source of papain did not affect the protein bait recovery, the pH and protein concentration though colour of bait differed for crude fruit latex papain bait (dark brown) and skin peel papain bait (light brown). The bait preparations had equal attractance to male and female B. invadens. Mean attractance to protein baits produced

with fruit latex and skin peel papain baits were between 25.00 ± 7.56 % and 47.50 ± 11.09 % respectively for males, 25.00 ± 13.13 % and 32.86 ± 8.23 % for female flies. Similarly, female flies showed equal affinity to feed on the different protein baits in a choice assay. However, flies reared on the no papain protein bait (control) were more fecund than flies reared on the local laboratory diet formulation. There was a relation between survival duration and fecundity; high fecundity resulted in reduced survival duration for flies reared on the different protein baits and laboratory diet formulation. Papain extracted from the ―Red lady‖ pawpaw fruit latex and skin peels are as effective as the commercial papain for proteolysis of proteins, therefore, local protein baits can now be prepared using the extracted local papain for Bactrocera invadens control in Ghana. In conclusion, an aqueous two-phase extraction of 15 % (NH4)2SO4 – 8 % PEG is effective for papain extraction from the ―Red lady‖ pawpaw fruit latex which can be used to produce local protein baits. Crude papain from local pawpaw variety is as effective as commercial papain for the proteolysis of protein bait. The phase concentration of the aqueous two-phase extraction system should be evaluated to improve especially the papain extraction from the pawpaw fruit skin peel. Cobalt-60 gamma radiation did not improve the purity of the crude papain, however, it can be a suitable treatment to enhance or maintain the proteolytic activity.