Department of Horticulture

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Author: search.filters.author.Musa, Peter Dennis

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    Development and Reproduction of Sweet Potato Whitefly Bemisia tabaci (Homoptera; Aleyroididae) on Four Vegetable Crops in Southern Sierra Leone
    (Scientific Research Publishing, 2025) Musa, Peter Dennis
    Bemisia tabaci is a polyphagous herbivore that feeds on a wide range of horticultural and ornamental crops cultivated under diverse ecological zones. In Sierra Leone, B. tabaci is found to infest a wide range of vegetable crops by directly feeding on phloem sap thereby inducing physiological disorders, and also serve as a vector to gemini viruses. Invariably the destructive feeding of B. tabaci affects the productivity and aesthetic values of vegetables and other horticultural crops and hence is considered a serious economic pest. A bioassay experiment was carried out by rearing B. tabaci populations on four vegetable crops under controlled laboratory conditions to determine its life table and demographic parameters. Results showed that the intrinsic rate of growth which measures the population size and growth pattern was highest for populations reared on tomato crops with the following values: rm 0.145 female female−1 day−1, the gross reproduction rate (Ro), and finite growth rate λ were highest for population reared on tomato, correspondingly the development period from egg-adult emergence was shortest with a value of 26 d. Conversely, the computed demographical parameters rm, λ and Ro for the population reared on sweet pepper were 0.106 female female−1 day−1 respectively, with a corresponding development period egg-adult emergence as 36d. The computed biological parameters for okra and garden egg varied with intermediary values between tomato and pepper host materials. The survivorship rates were quite significant for the smaller instars (Instars 1-III) with over 80% surviving to pre-pupa and pupa stage for the populations reared for all the test materials. High mortality was noticed for the pre-pupa and pupa stages as their survival rates were significantly low compared to the high survival rates of the smaller instars. Less than 50% of pupae failed to emerge to adults except for populations reared on tomato test materials where 52% emerged to adults. The study indicated tomato as the most suitable host among the four vegetable crops. Although life table and demographic parameters are invaluable information for forecasting pest populations and help in designing pest management efforts, further investigations such as the economic threshold and economic injury levels of B. tabaci population are requisite decision tools for sound pest management decisions of B. tabaci on these vegetable crops. The information obtained from this investigation would be quite relevant for extension service and pest management practitioners where mixed vegetable farming is a common practice.
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    Evaluation of the Functional Response of Seven Spotted Lady Bird Beetle Coccinella septumpunctata (Coleoptera: Coccinellidae) on Five Varying Densities of Bemisia tabaci (Homoptera: Aleyrodidae) Population under Controlled Laboratory Conditions
    (2026-02-12) Musa, Peter Dennis
    Bemisia tabaci is a cosmopolitan polyphagous insect undermining the productivity of a wide range of crops including but not limited to horticulture, ornamental and vegetable crops. The management of B.tabaci has been dominated by the use of broad-spectrum insecticides, though having the unique feature of reducing pest population below action threshold and economic injury level, their usage is however characterized with side effects including but not limited to environmental degradation and development of resistant genes in insects. The use of natural enemies (biological control) is considered more sustainable and viable option, environmentally friendly and poses no risk to users. Among the numerous biological control opportunities, the use of coccinellid beetles potentially proves to be quite promising and are abundantly found in insect infested vegetable fields. The ability of natural enemies as effective biological control agents is highly vested in their respond to density of preys density-dependent which can be measured in terms of their functional responses focusing on instantaneous search rates (a) and handling time (Th) as distinct and invaluable parameters. A bioassay cage experiment under laboratory conditions was carried out to evaluate the functional response of seven spotted lady bird beetle C. septumpuntata late 4th instars, male and female adults respectively on varying densities of B. tabaci eggs, 2nd and 3rd instars. The results were normalized and nature of response curves of C. septempartite on these prey densities were characterized and determined as Type II functional response. The response curves monotonically declined with increased in pest density for the 4th instars , female and male adults when fed on 2nd instar larvae with female adults showing the highest instantaneous search rate 0.54 and lowest handling time 0.19 and maximum consumption of 10.95 prey-1hr-1 strongly indicating that the female beetles showed potential attributes as ideal biological control candidate compare to the male and late 4th instar counterparts when fed on the 2nd and 3rd instars. However, when beetles were offered with B. tabaci eggs , the 4th instars demonstrated least handling time 0.73 and higher attack rate 2.57 than the female and male counterpart correspondingly showing the highest satiation threshold 32.87 prey-1hr-1.Though the beetle demonstrated promising potential as an ideal candidate based on current laboratory findings providing insight on the possibility for mass rearing and subsequent utilization in biological control programs of agricultural pests , there is however need for further investigation under greenhouse and field scenarios. Meanwhile, the prospect of C. septumpunctata as an ideal biological control candidate on B. tabaci population is discussed.
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    Evaluation of Bioactive Ingredients of Arica papaya and Azadirachta indica on Development and Reproduction of Bemisia tabaci (Homoptera: Aleyroididea)
    (2026-02-06) Musa, Peter Dennis
    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±2OC 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 2nd instars >3rd instars > pupa at (P<0.0.001). LT50 values varied across developmental stage, 2nd 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 2nd instars <3rd 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 Ro, ƛ, rm 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.