The absorption of cypermethrin in the grasshopper Melanoplus sanguinipes (Fab.): Effects of volatilisation,temperature, age,sex and parasitisation by Malameba locustae (King and Taylor) |
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| Authors: | Christopher F Hinks Neil D Westcott Randy A Reichle David T Spurr |
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| Abstract: | The residues from metered doses of cypermethrin were recovered from excised portions of grasshopper cuticle to determine losses by volatilisation. Residues from similar doses were also recovered from the cuticles of intact grasshoppers and from whole body homogenates after rinsing the cuticle, to determine rates of absorption and losses from metabolism. Residues were recovered from males and females one week and three weeks after fledging in grasshoppers infected with Malameba locustae and in uninfected ones. They were maintained at 15 or 30°C and sampled from each combination of factors at 4, 8, 16, 24, 30 and 48 h after treatment. There was no measurable loss of cypermethrin by volatilisation up to 72 h after application to excised portions of cuticle at either 15 or 30°C. In all combinations of factors, more cypermethrin was recovered externally (P <0.05) from grasshoppers held at 15°C than those held at 30°C and more from infected grasshoppers than from those that were uninfected. Significantly more cypermethrin was also recovered externally from males than from females (P <0.05) and more from infected one-week-old grasshoppers than those that were three weeks old. At 15°C there was a gradual trend towards accumulation of cypermethrin internally, but at 30°C an initial trend towards accumulation was followed by one of decline. Residual cypermethrin recovered could in general be related to the negative temperature coefficient of toxicity, to a decreased sensitivity to cypermethrin in infected grasshoppers and to an increased sensitivity in older grasshoppers. |
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