Toxicity and Anticholinesterase Activity of Two Halogenated Phosphorothioates to Boettcherisca peregrina
1 and Chrysomya megacephala
Relative toxicity of Ciba C-9491 (O
- (2,5-dichloro-4- iodophenyl) O,O
-dimethyl phosphorothioate) , and C-8874 (O
- (2,5-dichloro-4-iodophenvl) O,O
-diethyl phosphorothioate) to mature 3rd-stage larvae, 1- to 2-day-old pupae, and 3- to 4-day-old male and female adults of Boettcherisca peregrina
.(Robineau-Desvoidy) and Chrysomya megacephala
(F.) was investigated. In vitro and in vivo anticholinesterase activity and the correlation between toxicity and anticholinesterase activity of the 2 insecticides to the adult females of both species also were determined.
The insecticides were of low toxicity to the immature stages of both fly species. Based on the LD50
values, larvae of B. peregrina
were approximately 2 and 4 times more susceptible than the larvae of C. megacephala
to C-949! and C-8874, respectively. In terms of the LD95
values, B. peregrina
larvae were approximately 6 times more susceptible than the larvae of C. megacephala
to C-8874, but were equally susceptible to C-9491. Pupae of both species were highly tolerant to the insecticides, and dosage levels as high as 16,000 Mg/g resulted in less than 25% mortality.
In general, C. megacephala
adults were either as susceptible or more susceptible than B. peregrina
adults to both insecticides. At the LD50
levels, adults of both species were equally susceptible to topically applied C-9491, but after injection with C-9491, C. megacephala
adults were more susceptible than B. peregrina
.Females of both species were equally susceptible to the topical application of C-8874, hut C. megacephala
males were more susceptible than B. peregrina. C. megacephala
was more susceptible than B. peregrina
to injected C-8874 at the I.D,o level, but both species were equally susceptible at the LD50
The natural head cholinesterase activity of both species was similar when based on the number of heads needed to produce 80% hydrolysis of acetylcholine chloride after 30 minutes' incubation. However, based on the actual head "weights, the head cholinesterase of B. peregrina
was approximately 1.7 times more active than that of C. megacephala.
Sex had no effect on enzyme activity.
C-9491 and C-8874 were both moderate in vitro cholinesterase inhibitors and were equally effective in decreasing the enzyme activity of the head breis of both species. There was a direct correlation between insecticidal toxicity and in vitro head cholinesterase inhibition for the adult flies of B. peregrina
and C. megacephala.
On the other hand. there was no correlation between insecticidal toxicity and in vivo head cholinesterase inhibition. Both C-9491 and C-8874 were slow-acting insecticides and were weak in vivo inhibitors. In all cases, maximum inhibition was somewhat higher in dead flies than in surviving flies. Little or no recovery of cholinesterase activity occurred in surviving flies of either species treated with C-9491 or C-8874, but some enzyme recovery in dead flies was demonstrated.