Abstract
Experimentsconducted to study the toxic and biological effects of three chemicalinsecticides (chlorpyrifos, Lambda-Cyhalothrin, and Methomyl), onebiochemical insecticide (spinosad), and two bio-insecticides (Bacillusthuringiensis kurstaki Bt and Nucleopolyhedrovirus, NPV) against neonatelarvae of the pink bollworm, Pectinophora gossypiella (Saund.), were carried out underlaboratory conditions. The highest effect of tested pesticides on larvalmortalities was recorded after four days of feeding these larvae on treateddiet. Spinosad was the effective toxin (LC50=1.84 ppm) to neonatelarvae followed by chlorpyrifos (LC50= 3.06 ppm), Lambda-Cyhalothrin(LC50= 5.99 ppm) then Methomyl (LC50=23.50 ppm) but B.t.(74.84×104 I.U) and NPV (83.5×109 I.U) were the lowestones. LC50 treatments of neonate larvae with all tested insecticidesproduced reduction in larval and pupal weights especially Lambda-cyhalothrintreatment, (31.9 and 24.3 %, resp.) compared with untreated insects. Thedecreasing effect of all treatments observed in fecundity and life span ofadult females which reflected in very high percentages of insect sterility withchlorpyrifos (66.7%) and Methomyl (61%) treatments. Insignificant increase oftotal protein contents and activity of Glutathione-S-transferase enzyme wasdetected in tissues of LC50 treated larvae compared with untreated larvae,but a significant (23.5%) and highly significant (56.9%) increase in enzymeactivity were resulted by Chlorpyrifos and Spinosad treatments. A very highinhibition in activity of Acetylcholinesterase enzyme of larval tissues wasrecorded with NPV (61.3%), B.t. (58.8%), Lambda-Cyhalothrin (55.6%), Spinosad(54.4%), Chlorpyrifos (48.7%), and Methomyl (37.5%)treatments than untreated ones.
Highlights
Cotton is one of the most important cash crops in Egypt which plays a dominant role in the industrial and agricultural economy of the country
Bioassay: The toxic effect of Chlorpyrifos, Lambda-Cyhalothrin, Methomyl, Spinosad, Bt, and NPV was shown in Table 1 revealed that Spinosad treatment gave the highest toxic effect on neonate larvae of the pink bollworm (LC50 = 1.84 ppm and Toxicity index, T.I = 100%) Chlorpyrifos (3.06 ppm and 6.01%), Lambda-Cyhalothrin (5.99 ppm and 30.7%), and Methomyl was the lowest chemical insecticide (23.5 ppm and 7.8%)
Our data show that LC50 treatments of the tested insecticides produced several changes in biological aspects of the pink bollworm treated as neonate larvae
Summary
Cotton is one of the most important cash crops in Egypt which plays a dominant role in the industrial and agricultural economy of the country. The pink bollworm, Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae), is one of the most injurious cotton pests, because it is difficult to control with insecticides (Lykouressis et al, 2005). The bolls of cotton are the most susceptible to pink bollworm infestation from 12 to 30 days post bloom. Once a boll is “rock hard” in firmness, it is generally immune to infestation by newly hatched larvae. Environmental and health problems associated with chemical-based insecticides have prompted the search for ecologically acceptable pesticides. The application of chemical pesticides compatible with biological control is very important. The reduction of pesticide uses aroused increased economic profit and contributed to a cleaner environment and improved the health status of farmers (Hossain et al, 2004; Kouser and Qaim 2011; Abdullah et al, 2015)
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