No abstract

: The activity of teÑuthrin, carbofuran, terbufos and dieldrin in soil against eggs of di †erent ages of the southern corn rootworm, Diabrotica undecimpunctata howardi (Barber) (Coleoptera : Chrysomelidae) was determined. Embryological development following treatment with these insecticides was also investigated to determine the stage of developmental arrest. Generally, younger eggs were found to be more susceptible, dieldrin being the least and teÑuthrin the most potent ovicide of combined egg age mortalities. Terbufos and carbofuran were relatively inactive against older eggs compared with teÑuthrin. Terbufos stopped embryonic development at the time when acetylcholine esterase activity has been shown to commence. Carbofuran, dieldrin and teÑuthrin slowed but did not arrest embryonic development, although the two former compounds prevented eclosion to a greater degree than teÑuthrin, suggesting death during absorption of serosal Ñuids at eclosion. Neonate emergence following treatment of eggs with teÑuthrin resulted in death within a few hours. The results are discussed in relation to insecticidal action and permeability changes of egg membrane structure with age.

: The internal and external levels of topically applied soil insecticides, teÑuthrin, terbufos and dieldrin, to 3rd-instar larvae of the southern corn rootworm, Diabrotica undecimpunctata howardi (Barber), were monitored over 48 h. Symptomology of poisoning with 10 times the dose of the larval 72-h for LD 90 each chemical was observed over 48 h at various time points after treatment. Terbufos penetrated more rapidly than teÑuthrin or dieldrin, although internal levels of teÑuthrin and dieldrin had a longer-lasting plateau than terbufos. A 72-h treatment with teÑuthrin resulted in faster penetration and also faster dis-LD 30 appearance from the insect compared with the 10 ] 72-h dose over a 48-h LD 90 period. Recorded symptoms of poisoning included regurgitation of gut contents, defaecation and writhing and these are suggested to play an important part in voiding of the toxicants at lower (sub-lethal) treatment levels. The sub-lethal e †ects of teÑuthrin are discussed with respect to likely pest behavioural changes, such as anorectic response, after Ðeld treatment of a crop.

No abstract