Evaluation of Bioactive Ingredients of Arica papaya and Azadirachta indica on Development and Reproduction of Bemisia tabaci (Homoptera: Aleyroididea)

Abstract

Bemisia tabaci is a cosmopolitan pest affecting a wide range of crops including but not limited to horticultural and ornamental crops. Damage is caused through direct feeding on the phloem sap of host crops thereby inducing physiological disorders and   serving as vector causing viral diseases in insect population. Both forms of damage have direct consequences on crop production, productivity leading to drastic reduction of economic values of the crops .  Management of B. tabaci in Sierra Leone has been dominated by the use of broad-spectrum chemical pesticides, though having the intrinsic feature of reducing the pest population below the economic injury level, yet their usages are associated   with adverse effects on the environment, non-targets organisms  and development of resistant genes in insects . Equally important, cost and affordability of pesticides for large scale applications are being considered constant economic burden to smallholder farmers. These challenges have prompted to seek alternative substitutes to broad-spectrum chemical pesticides, with a paradigm shift of the use of plant derived bio-active ingredients significant from plants and fungi serving as bio-pesticides.  These bio-pesticides have proven to be quite useful in managing sap sucking insects like B. tabaci though their abilities have not been fully exploited in under Sierra Leonean circumstance . This investigation aimed at determining the impact of bio-active ingredients of Neem and Papaya on the reproduction and development of B. tabaci under controlled laboratory conditions. Concentrations of the active ingredients of A. papaya and A.indica  were prepared and serially diluted at different concentrations and assayed against eggs and developmental stages of B. tabaci in bioassay cages and maintained under controlled laboratory conditions of 25±2^OC and photoperiodism of 12:12 (L:D).   No significant impact     % hatchability (p=0.0001) as > 60% of eggs hatched into crawlers, however    larval mortality was dose-dependent, larval mortality was significantly impacted and varied with age of immature in the order 2^nd instars >3^rd instars > pupa at (P<0.0.001). LT₅₀ values varied across developmental stage, 2^nd instars required 2.54 and 4.3 days to inflict 50% mortality in population treated with Neem and Papaya respectively. Larval mortality was dose-dependent with mortality proportionally increasing with increased in concentration of the active ingredients.   The LC₅₀ values strongly correlated with developmental stage and concentration in the order 2^nd instars <3^rd instars < pupa for neem and papaya extracts respectively. Moreover, the extracts impacted the population dynamics of B. tabaci as the population parameters were significantly influenced by the toxicity of the extracts suppressing the growth and population parameters as compared to the control. Comparatively, the neem extracts significantly impacted the demographic parameters R_o, ƛ, r^m   13.66, 1.103, 0.018 as compared to A. papaya extract 18.97, 1.106 0.101 and control 23.56 1.130 , 0.123 respectively . The importance and potentials of A. indica and   A. papaya as effective bio-pesticides for sustainable management B. tabaci were well highlighted and discussed.