Pyrrole Insecticide Research Articles

Chlorfenapyr: A pyrrole insecticide for the control of pyrethroid or DDT resistant Anopheles gambiae (Diptera: Culicidae) mosquitoes

Owing to the development and spread of pyrethroid resistance in Anopheles gambiae in Africa there is an urgent need to develop alternative insecticides to supplement the pyrethroids. Chlorfenapyr is a pyrrole insecticide first commercialized for the control of agricultural pests and termites. Performance against An. gambiae bearing kdr (pyrethroid and DDT resistance) or Ace-1 R insensitive acetylcholinesterase (organophosphate and carbamate resistance) mechanisms was studied using a variety of adult bioassay tests including a simulated-experimental hut system (tunnel tests) that allows uninhibited mosquito behaviour/insecticide interactions. Strains resistant to pyrethroids and organophosphates showed no cross resistance to chlorfenapyr. In cone bioassays on treated netting the mortality of adult mosquitoes showed an unexpected curvilinear response, with highest mortality occurring at intermediate dosages. Adults expressed irritability to chlorfenapyr at higher dosages, which might explain the dosage–mortality trend. Toxic activity of chlorfenapyr was slow compared to conventional neurotoxic insecticides and additional mortality occurred between 24 h and 72 h. In tunnel tests, the dosage–mortality trend showed a more typical sigmoid response and most mortality occurred during the first 24 h. Mosquito penetration through the holed, treated netting showed only limited inhibition and blood-feeding was not inhibited. Mortality rates in the kdr strain exposed to chlorfenapyr treated netting in tunnel tests were much higher than with permethrin treated netting over the same 100–500 mg/m 2 dosage range. Chlorfenapyr has potential for malaria control in treated-net or residual spraying applications in areas where mosquitoes are pyrethroid resistant. For treated-net applications chlorfenapyr might be combined with pyrethroid as a mixture to provide personal protection as well as to give control of resistant mosquitoes.

Investigations into the Parallel Synthesis of Novel Pyrrole-Oxazole Analogues of the Insecticide Pirate

Investigations into the parallel synthesis of selected analogues of a structurally unique pyrrole-oxazole analogue of the pyrrole insecticide pirate, are reported. Acylaminoketone salts were obtained from ketobromides in moderate to high yields and excellent purity. A number of N-tosyl pyrroles were obtained; however, formation of the target acyl tosyl pyrroles was thwarted by the stereoelectronic effects of the pyrrole substituents. During the pyrrole subunit chemistry, an interesting pyrrole derivative, vinyl pyrrole, was isolated. By restricting diversity to the aryl subunit, the parallel synthesis of selected pyrrole-oxazoles in moderate purity, was achieved when electron-donating or no groups were present on the aryl ring.

Increased Susceptibility of Pyrethroid-Resistant Tobacco Budworm (Lepidoptera: Noctuidae) to Chlorfenapyr

Chlorfenapyr is a new pyrrole insecticide with a new mode of action. Its toxicity to adult Heliothis virescens (F.) is negatively correlated with cypermethrin toxicity by the equation y = 1.065x + 3.513 (r = 0.97), where x = log LC50 cypermethrin, y = log LC50 chlorfenapyr. Chlorfenapyr was most toxic to adults of a pyrethroid-resistant strain (LC50 = 70.1 µg per vial in adult vial tests at 48 h). The negative correlation was not observed in neonates fed with chlorfenapyr impregnated diet. Cross-resistance to chlorfenapyr in Pyrethroid-R larvae was 2.3-fold with the diet method, compared with 28-fold resistance to cypermethrin. Cross-resistance was only significant in diet tests. Chlorfenapyr was as effective as insecticides registered for cotton against H. virescens. Inheritance data showed that only 1 allele is necessary from the Pyrethroid-R strain to produce complete susceptibility to chlorfenapyr in adults. The susceptibility to chlorfenapyr is a dominant trait, and the resistance to chlorfenapyr is a recessive trait. In a backcross experiment, one-half the progeny were highly susceptible to chlorfenapyr and one-half were highly resistant, indicating segregation of a single factor. The mechanism for this effect could be caused by pleiotropy (i.e., a gene for pyrethroid resistance controls increased detoxication to cypermethrin while also increasing the susceptibility of chlorfenapyr). The pyrethroid-resistant gene is likely to be identical to, or closely linked to, the gene that gives increased susceptibility to chlorfenapyr.