Abstract
The toxicity of seven biorational insecticides [five insect growth regulators (Buprofezin, Fenoxycarb, Pyriproxyfen, Methoxyfenozide, and Tebufenozide) and two oil-extracts of neem and bitter gourd seeds] against Bemisia tabaci and their selectivity for its parasitoid, Encarsia formosa were evaluated in laboratory and field conditions for 2 years (2018–2019) in Pakistan. Toxicity results demonstrate that Pyriproxyfen, Buprofezin, and Fenoxycarb proved to be effective (80–91% mortality and 66.3–84.2% population-reduction) against B. tabaci followed by Methoxyfenozide, Tebufenozide (50–75% mortality and 47.8–52.4% population-reduction), and then oil-extracts of neem and bitter gourd (25–50% mortality and 36.5–39.8% population-reduction) in the laboratory [72 h post-application exposure interval (PAEI)] and field trails (168 h PAEI), respectively. All tested biorationals, except Methoxyfenozide [(slightly-harmful/Class-II), i.e., causing mortality of parasitoids between a range of 25–50%] and Tebufenozide [(moderately-harmful/Class-III), i.e., causing mortality of parasitoids between the ranges of 51–75%], proved harmless/Class-I biorationals at PAEI of 7-days in the field (parasitism-reduction < 25%) and 3-days in the lab (effect < 30%). In laboratory bioassays, exposure of parasitized-pseudopupae and adult-parasitoids to neem and bitter gourd oils demonstrated that these compounds proved harmless/Class-I biorationals (< 30% mortality). Alternatively, Pyriproxyfen, Buprofezin, Fenoxycarb, Methoxyfenozide, and Tebufenozide were slightly-harmful biorationals (30–79% mortality) against the respective stages of E. formosa. We conclude that most of the tested biorationals proved harmless or slightly harmful to E. formosa, except tebufenozide after PAEI of 7-days (168 h) in the field and, therefore, may be used strategically in Integrated Pest Management (IPM) of B. tabaci.
Highlights
Bemisia tabaci, is a serious pest of cotton and many other vegetables and orchard crops[1,2,3,4]
The laboratory and field studies in the present study demonstrate that adults and nymphs of B. tabaci show increased mortality in the laboratory and higher population reduction in field when exposed to pyriproxyfen followed by buprofezin, fenoxycarb, methoxyfenozide, tebufenozide neem-extract, and bitter gourd-extract
The results of the present study show that at the maximum post-application exposure interval (PAEI) (168 h), pyriproxyfen, buprofezin, fenoxycarb, and methoxyfenozide were in Class-II biorationals, neem and bitter gourd oils were Class-I biorationals, and tebufenozide was in Class-III biorationals when emergence and mortality of E. formosa were recorded inside the treated host pseudopupae in lab bioassay
Summary
Bemisia tabaci, is a serious pest of cotton and many other vegetables and orchard crops[1,2,3,4]. They disrupt hormonal regulation and result in abnormal molting, growth, and development in several insects They are used for the control of many insect species acting as ecdysone agonists (tebufenozide and halofenozide), juvenile hormone mimic (pyriproxyfen) and chitin synthesis inhibitors (benzoylphenylureas and buprofezin). Fenoxycarb acts as a juvenile hormone mimic and has been documented as an effective molecule for controlling various insect pests infesting economic crops, ornamentals, and fruits It interrupts the metamorphosis, growth, and development of all insect life stages and inhibits oogenesis and the development of o varies[40]. Tebufenozide and methoxyfenozide as IGRs act both as stomach and contact poisons with a 3-week residual activity period Both result in mortality by a failure of feeding in target insects or by disrupting the normal process of molting, in lepidopteran pests[43,44]. The impact of these biorational insecticides is not well understood on the whitefly and its parasitoid in Bt cotton
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