Abstract
The effects of three bio-insecticides Azatrol [neem: 1.2% azadirachtin A and B], Molt-X [neem: 3% azadirachtin], and Conserve SC [spinosad; 11.6% spinosyn A and spinosyn D], applied at different concentrations were evaluated on Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) under both laboratory and greenhouse conditions. Laboratory bioassays demonstrated that both neem-based insecticides were repellent to adult whiteflies in a dose-dependent manner. The amounts and frequency of honeydew excretion were significantly reduced up to 0.95 by foliar application of these insecticides at the labeled rate, as compared to untreated plants, with the neem products displaying greater effects on food uptake than spinosad. Reduced fecundity and egg hatch also were associated with these bio-insecticides. The bio-insecticides decreased significantly the survival of nymphs, egg hatch and adult emergence when applied systemically via the roots. However, the impacts of neem-based insecticides on all parameters tested were greater than that of spinosad. The results indicate that the biologically based formulations tested were effective in suppressing whitefly abundance and acting as an efficient repellent, though they were not able to completely inhibit food intake. The repellent and antifeedant activities of such natural products render plants unattractive to B. tabaci , thus potentially reducing the incidence of viral diseases transmitted by this pest. The systemic properties of these formulated biopesticides minimize their rapid degradation by strong ultraviolet light and their adverse effects on non-target organisms.
Highlights
The agricultural sector of Jordan is one of the most important economic pillars for integrated development in Jordan, constituting 16% of the country's exports [1]
Indirect damage can arise from the contamination of fresh-market crops with honeydew and sooty mold, which adversely affects some physiological processes in the host plant and may renders crops unsaleable [7]
In two-choice assays, whiteflies given a choice of either treated or untreated cucumber plants had a lower tendency to colonize treated plants; both neem-based insecticides showed up to 0.68 repellency in non-choice tests with higher levels of repellency elicited by increasing concentrations (F = 242.91; df = 6, 63; P < 0.0001) (Table 1)
Summary
The agricultural sector of Jordan is one of the most important economic pillars for integrated development in Jordan, constituting 16% of the country's exports [1]. Infestation by pestiferous insects is one of the main constraints for crop productivity in the country, among them the whitefly Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) This pest is found worldwide, where it produces several generations per year and attacks hundreds of plant species in numerous plant families grown both in the field and under greenhouse conditions [2,3]. B. tabaci can inflict severe injury directly by depriving the plant of its essential nutrients, eventually resulting in a wilting, deformed plant with premature leaf senescence and retarded growth [4] It disrupts the host plant by injecting toxic saliva while feeding on the plant; this causes physiological changes in plant tissue such as uneven ripening of tomato fruits and discoloration of cucurbit foliage [5,6]. B. tabaci is one of the most important vectors of several plant viruses throughout the world [8,9]
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