Mortality and reproductive effects of ingested spinosad on adult bollworms

Upon emergence from their pupal cells, bollworm, Helicoverpa zea (Boddie), adults actively seek and feed on plant exudates before they disperse and reproduce on suitable host plants. This nocturnal behavior of the bollworm may be exploited as a pest management strategy for suppression of the insect by using an attractant/stimulant mixed with an insecticide to induce feeding to cause adult mortality or reproductive reduction/inhibition. This study aimed to determine in the laboratory whether or not spinosad when mixed with sucrose solution as a feeding stimulant and ingested by bollworm could influence mortality and reproduction of the insect.

Sublethal concentrations of spinosad fed to laboratory-reared females confined with males significantly reduced percentage hatch of eggs at 0.1 mg L(-1), and it was reduced to near zero at 2.5 mg L(-1) when compared with females fed 2.5 M sucrose solutions only. The lethal concentration (LC(99)) for males captured from the field in sex-pheromone-baited traps was 73 mg L(-1) for 24 h response. Proboscis extension response was not inhibited significantly even at 10 g L(-1). In spite of a 137-fold increase in lethal dose concentration, spinosad did not inhibit feeding.

A detailed study of laboratory-reared and field-collected bollworm adults relative to mortality and reproduction after ingestion of spinosad indicates that spinosad would be useful in an attract-and-kill strategy to control the insect when mixed with a feeding attractant/stimulant. Field validation of the data is warranted.