Area-Wide Survey of Chlorantraniliprole Resistance and Control Failure Likelihood of the Neotropical Coffee Leaf Miner Leucoptera coffeella (Lepidoptera: Lyonetiidae)

The Neotropical coffee leaf miner, Leucoptera coffeella (Guérin-Mèneville & Perrottet, 1842), is a key pest species of unshaded coffee plantations in Neotropical America, particularly in Brazil, where pest management involves intensive insecticide use. As a consequence, problems of resistance to conventional insecticides are frequent, and more recently developed insecticide molecules, such as diamide insecticides, are at risk of becoming ineffective. Thus, a survey of resistance to the diamide insecticide chlorantraniliprole was carried out in high-yield coffee-producing areas in the State of Bahia, Brazil. The likelihood of control failure with this insecticide was also assessed. Spatial dependence among the insect sampling sites was assessed and spatial mapping of chlorantraniliprole resistance and risk of control failure was carried out. The frequency of chlorantraniliprole resistant populations was high (34 out of 40 populations, or 85%), particularly in western Bahia, where 94% of the populations were resistant. Resistance levels ranged from low (<10-fold) to moderate (between 10- and 40-fold) with more serious instances occurring in western Bahia. This results in lower chlorantraniliprole efficacy among these populations, with a higher risk of control failure and exhibiting spatial dependence. These findings invite attention to problems with the intensive use of this relatively recent insecticide and demand management attention, but they suggest that local, farm-based management efforts are likely to be the most effective actions against resistance problems in this pest species.

Impact of Imidacloprid Soil Drenching on Survival, Longevity, and Reproduction of the Zoophytophagous Predator Podisus maculiventris (Hemiptera: Pentatomidae: Asopinae)

Systemic insecticides when applied as seed treatments or soil drenches are often more toxicologically selective for natural enemies than target pests. This may not be the case, however, for omnivorous predators, which are at risk of extended exposure to systemically applied pesticides through ingestion while feeding on treated plants for nutrients or water. Such exposure may kill or have sublethal consequences for these natural enemies, compromising their role as biocontrol agents of agricultural pest species. The spined soldier bug, Podisus maculiventris (Say) (Hemiptera: Pentatomidae: Asopinae), is an important zoophytophagous biocontrol agent (i.e., able to substitute zoophagy by phytophagy for survival) that may be exposed to systemic insecticides in many agricultural systems. We, therefore, examined effects on P. maculiventris following exposure to cabbage plants subject to soil-drench treatments with imidacloprid, a systemic neonicotinoid insecticide. Predator survival, development, body weight, and reproduction were recorded. Imidacloprid significantly affected nymph survival and adult emergence, but not duration of the nymphal period or adult body weight. At one-twentieth the recommended field rate for whitefly and aphid management, imidacloprid treatments reduced longevity, fecundity, and fertility of female predators. These findings demonstrate that soil treatments with systemic insecticide can negatively impact zoophytophagous natural enemies.

Imidacloprid Soil Drenches Affect Weight and Functional Response of Spined Soldier Bug (Hemiptera: Pentatomidae)

There are ongoing concerns of potential direct and indirect lethal and sublethal effects of insecticides on nontarget arthropod populations. The risk to natural enemies from systemic insecticides is mainly through exposure to the active ingredient by ingestion, and such risk may be elevated for omnivores that feed on treated plants, as well as herbivores that also feed on those same treated plants. Podisus maculiventris (Say), an important natural enemy in many agricultural systems, can be potentially exposed to the neonicotinoid imidacloprid when ingesting contaminated prey and feeding on plants subjected to soil-drench applications of this compound. In the current study, we examined the potential impact of imidacloprid soil drenches on some functional and morphological endpoints. Cabbage plants were treated with soil drenches of imidacloprid that corresponded to half and full recommended labels rates against whiteflies and aphids. Fourth instar diamondback moth, Plutella xylostella (Linnaeus) (Lepidoptera: Plutellidae), larvae on plants were used as prey in our experiments; P. xylostella is not a target of imidacloprid applications but may co-occur with other pests in systems where the insecticide is applied. We found that exposure to imidacloprid-treated plants did not cause significant mortality neither to P. maculiventris nor to P. xylostella, but both treatment concentrations impaired the predation, with consequences for predator weight gain during the assessment period. Our results corroborate those from other studies and demonstrate that effects from systemic insecticides can transcend trophic levels to affect natural enemies indirectly, such as through exposure from feeding on pests not targeted by the insecticide.