Multiple Factors Mediate Insecticide Toxicity To A Key Predator For Cotton Insect Pest Management

Mortality of agricultural pests caused by arthropod predators is a valuable ecosystem service for crop production. The earwig, Euborellia annulipes (Lucas), attacks different pest species in various crop ecosystems, including larvae and pupae of the boll weevil, Anthonomus grandis grandis (Boh.). Despite such biological control, cotton pest management remains heavily dependent on synthetic insecticides. In this study, multiple factors were assessed to measure the selectivity of insecticides used against sap-sucking and chewing cotton pests for two E. annulipes populations. Nymphs and adults of E. annulipes were exposed to the insecticides in two ways: ingestion of contaminated prey, and contact with dried residues on either inert surfaces or treated plants bearing prey. Pymetrozine, chlorantraniliprole, and spinetoram had little effect on the predator regardless the tested earwig population, life stage, or the route of exposure. Cyantraniliprole affected the predator in some life stages and through some types of contact. Pyriproxyfen was harmless to adult earwigs, but prevented normal development of nymphs to adults. Chlorfenapyr, indoxacarb, lambda-cyhalothrin, chlorpyrifos, dimethoate, and malathion were harmful to the predator regardless earwig life stage or method of exposure. The negative impact was diminished when exposure occurred on plants with predator allowed to shelter in the soil. The results indicate that insecticide selectivity outcome is a multi-factor driven by the insecticide, predator life stage and the redator’s behavior. Therefore, testing different predator life stages via several routes of exposure, without denying the insect the opportunity to engage in its normal behaviors can provide better estimates of insecticide selectivity.

Insecticide selectivity to Ooencyrtus submetallicus (Hymenoptera: Encyrtidae) under extended laboratory conditions

ABSTRACT Bioassays to evaluate the selectivity of pesticides to beneficial organisms are important tools to discriminate products compatible with biological pest control programs. This study aimed to evaluate the effects of the main insecticides used in the soybean crop on the egg parasitoid Ooencyrtus submetallicus (Hymenoptera: Encyrtidae). The tested treatments (active ingredients) were: methomyl, lambda-cyhalothrin + thiamethoxam, beta-cyfluthrin + imidacloprid, novaluron and teflubenzuron, in the highest doses indicated by the manufacturer for the soybean crop, and a control treatment (water). The evaluations enabled to calculate the mortality and parasitism capacity of adults exposed to the pesticides, in addition to the sex ratio of their descendants. Methomyl and lambda-cyhalothrin + thiamethoxam were classified as Class 4 (harmful), beta-cyfluthrin + imidacloprid as Class 3 (moderately harmful), and novaluron and teflubenzuron as Class 1 (harmless). The products classified as Class 3 and Class 4 should, as much as possible, be replaced by insecticides selective to O. submetallicus.