Toxicity of fenthion to Anastrepha fraterculus (Wied.) (Diptera:Tephritidae): dose response analysis

Abstract

Three toxicological bioassays were performed in two F1 south Brazilian field populations of Anastrepha fraterculus (Wied.). Lethal doses of fenthion (50% and 90%) were estimated in two bioassays, with oral administration, and with residual contact bioassay. Results of topical bioassays using fenthion diluted in alcohol, acetone or water were inconsistent. Samples treated with acetone or alcohol diluents presented high mortality (>10%), while the samples treated with water diluent showed a non linear response between dose and mortality. The residual contact bioassay was significatively more toxic when compared to a feeding bioassay, occurring equal slopes in males and females in the populations analysed. Additional test showed that insects did not discriminate between diets with and without fenthion.

Controle químico de Anastrepha fraterculus (Wied.) (Diptera: Tephritidae) em laboratório

“…Os inseticidas foram oferecidos numa solução/suspensão aquosa associada à mel a 2,5%, através de um rolete de algodão inserido em um tubo de 10mL. Após o preparo das soluções/suspensões, foi adicionado 1g L -1 de corante vermelho Ponceau (Sigma Chemical Co.) para atuar como indicador do consumo do inseticida, observado através da cor vermelha no abdômen dos insetos (CRUZ et al, 1997).…”

Age and time exposure-related toxicity of fenthion to male and female Anastrepha fraterculus (Wied.) (Diptera: Tephritidae)

“…The A. fraterculus population was collected in the town of São Joaquim, SC, Brazil from fruits of guava (Feijoa sellowiana). It was reared in conditions described by Da Cruz et al (1997). The experiments were carried out using the first generation of field collected fruit-flies; this procedure avoids loss of genetic variability that may decrease when the population is reared for many generations under laboratory conditions.…”

“…[0,0-dimethyl-0,-(methylmercapte-4-methylphthiophenyl)thiophosphate 0,0-dimethyl-0-(3-methyl-4methylthio-phenyl) phosphorothionate] 500 CE was used in a 10 ppm concentration. The insecticide manipulation and glass preparation were made as described by Da Cruz et al (1997) for the residual contact bioassay. Each of the following experiments was replicated five times, including the controls; 10 males and 10 females were used in each replication.…”

“…The intoxication effect was estimated using the initial appearance time of the rapid wing beat pattern of behavior. For this analysis, Petri dishes previously treated with fenthion were used as described in residual contact bioassay (Da Cruz et al 1997) . The samples were observed at 5 min intervals until more than 95% showed intoxication effects.…”

“…A recent study in A. fraterculus (Da Cruz et al 1997) showed differential fenthion toxicity in three classic bioassays: feeding, topical contact and residual contact. The insects exposed to residual contact were 18 times more susceptible than those exposed by feeding bioassay.…”