spinetoram and cyhalothrin

Many countries in Latin America have recently experienced outbreaks of Zika and chikungunya fever, in additional to the usual burden imposed by dengue, all of which are transmitted by Aedes aegypti in this region. To identify potential larvicides, we determined the toxicity of eight modern insecticides to A. aegypti larvae from a colony that originated from field-collected insects in southern Mexico. The most toxic compounds were pyriproxyfen (which prevented adult emergence) and λ-cyhalothrin, followed by spinetoram, imidacloprid, thiamethoxam, and acetamiprid, with chlorantraniliprole and spiromesifen the least toxic products. Field trails performed in an urban cemetery during a chikungunya epidemic revealed that insecticide-treated ovitraps were completely protected from the presence of Aedes larvae and pupae for 6 and 7 weeks in spinosad (Natular G30) and λ-cyhalothrin-treated traps in both seasons, respectively, compared to 5-6 weeks for temephos granule-treated ovitraps, but was variable for pyriproxyfen-treated ovitraps with and 1 and 5 weeks of absolute control in the dry and rainy seasons, respectively. Insecticide treatments influenced the mean numbers of Aedes larvae + pupae in each ovitrap, mean numbers of eggs laid, and percentage of egg hatch over time in both trials. The dominant species was A. aegypti in both seasons, although the invasive vector Aedes albopictus was more prevalent in the rainy season (26.7%) compared to the dry season (10.2%). We conclude that the granular formulation of spinosad (Natular G30) and a suspension concentrate formulation of λ-cyhalothrin proved highly effective against Aedes spp. in both the dry and rainy seasons in the cemetery habitat in this region.

Topics: Aedes; Animals; Cemeteries; Chikungunya Fever; Dengue; Drug Combinations; Insect Vectors; Insecticides; Larva; Macrolides; Mexico; Neonicotinoids; Nitriles; Nitro Compounds; ortho-Aminobenzoates; Oxazines; Pupa; Pyrethrins; Pyridines; Spiro Compounds; Temefos; Thiamethoxam; Thiazoles; Zika Virus Infection

Agricultural organisms, such as insect herbivores, provide unique opportunities for studies of adaptive evolutionary processes, including effects of insecticides on movement and oviposition behavior. In this study, Brassica leaves were treated with one of two non-systemic insecticides and exposed to two individual strains (referred to as single or double resistance) of diamondback moth (Plutella xylostella) (DBM) exhibiting physiological resistance. Behavioral responses by these two strains were compared as part of characterizing the relative effect of levels of physiological resistance on the likelihood of insects showing signs of behavioral avoidance. For each DBM strain, we used choice bioassays to quantify two possible types of behavioral avoidance: 1) females ovipositing predominantly on leaf surfaces without insecticides, and 2) larvae avoiding insecticide-treated leaf surfaces. In three-choice bioassays (leaves with no pesticide, 50% coverage with pesticide, or 100% coverage with pesticide), females from the single resistance DBM strain laid significantly more eggs on water treated leaves compared to leaves with 100% insecticide coverage (both gamma-cyhalothrin and spinetoram). Females from the double resistance DBM strain also laid significantly more eggs on water treated leaves compared to leaves with 100% gamma-cyhalothrin, while moths did not adjust their oviposition behavior in response to spinetoram. Larvae from the single resistance DBM strain showed a significant increase in mobility in response to both insecticides and avoided insecticide-treated portions of leaves when given a choice. On the other hand, DBM larvae from the double resistance strain showed a significant decrease in mobility in response to insecticides, and they did not avoid insecticide-treated portions of leaves when given a choice. Our results suggest that pest populations with physiological resistance may show behavioral avoidance, as resistant females avoided oviposition on leaves without gamma-cyhalothrin. Thus, physiological resistance and behavioral avoidance do not appear to be controlled by the same selection pressures, and the mechanisms responsible for behavioral avoidance may vary among life stages. Our analysis also suggested that a population with lesser physiological resistance to insecticides may be under a stronger selection pressure and therefore be more likely to develop avoidance behaviors than a population with higher levels of physiological resistance.

Topics: Agriculture; Animals; Behavior, Animal; Biological Assay; Female; Insecticide Resistance; Insecticides; Macrolides; Moths; Nitriles; Oviposition; Plant Leaves; Pyrethrins; Species Specificity