Current resistance status to temephos in Aedes aegypti from different regions of Argentina

In Argentina, more than 25,000 cases of dengue were reported in the summer of 2009, even in provinces where the disease was formerly absent. We analysed the susceptibility levels to the larvicide temephos in seven populations of Aedes aegypti, the primary vector of dengue, collected during summer 2007/2008, using the susceptible Rockefeller strain as a control. Although no control failures were observed during the experiment, a majority of the lethal concentration and resistance ratio values indicate an incipient resistance. An integrative program to monitor the resistance of Ae. aegypti to insecticides is needed in the country.

Synthesis and bioactivity of new phosphorodithioates derived from N-substituted maleamic esters

1. A new series of organophosphorus compounds derived from N-substituted maleamic esters by reaction with dimethyl and diethyl phosphorodithioic acid was synthesized. 2. Two isomers, with chemical structures analogous to malathion were obtained for each maleamic ester assayed. 3. They were characterized, and their toxicity against a resistant strain of Musca domestica (strain G), a susceptible one (strain RAC) and Triatoma infestans (vector of Chagas' disease) were measured. 4. The structural chemical modification introduced by replacing a carboxyester group for a N-substituted amido one, reverted the resistance obtained for malathion. 5. Replacement of methyl by ethyl dithiophosphoric acid did not introduce significative differences. 6. In the case of Triatoma infestans, the synthesized compounds were less active than malathion.

Feeding and mating deterrency by sulfhydryl reagents in Triatoma infestans

Topical application of different sulfhydryl (SH) reagents in acetone solution resulted in a deterrence of the feeding activity of Triatoma infestans nymph V. The ED50 for topical application of N-ethylmaleimide (NEM), the more active compound assayed, was 8.9 micrograms/insect. This effect showed a dose-dependent reversibility. We also observed feeding deterrency when a gauze cloth impregnated with NEM was located between the food source and the nymphs. After topical NEM treatment, mating deterrency was assessed by counting spermatophores dropped and eggs laid. When a population of adult insects, nymphal stages and eggs was reared in a cage containing filter papers treated with 0.4 mg/cm2 of NEM, a significant decrease of population density was seen after 200 days of exposure. Weekly replacement of filter papers impregnated with 0.13 mg/cm2 NEM for a period of one year enabled population control to be maintained. Antifeeding and antimating effects of NEM in Triatoma infestans and the resulting population control could be attributed to a chemoreceptor blockage produced by SH reagents.

Activity of the insect growth regulator fenoxycarb (RO-13-5223) on Triatoma infestans (Hemiptera)

1. Fenoxycarb (RO-13-5223) exhibits a strong juvenile hormone type of activity against Triatoma infestans. 2. Topical treatment of last-stadium nymph with the juvenoid caused the formation of superlarvae, adult-larvae intermediates and adultoids. The ED50 was 0.02 microgram/insect. 3. Taking into account abnormalities in oceli, head, thorax, legs, wings, abdomen, conexivo and external genitalia, a scoring system to evaluate the retention of juvenile characters after moulting was developed. 4. Intermediate dose of the juvenoid produced the prolongation of the last instar nymph. 5. Abnormal individuals formed composite cuticles possessing both nymph and adult morphological features.