Toxicity of acaricides to and the behavioural response of Steneotarsonemus concavuscutum (Acari: Tarsonemidae)

Abstract

Steneotarsonemus concavuscutum Lofego and Gondim Jr. causes chlorosis, necrosis, deformation, resinosis and death of coconut fruit (Cocos nucifera L.). These types of damage are commonly interpreted to result from Aceria guerreronis Keifer. The control of mites in coconut fruits is carried out primarily by acaricide applications. However, no records exist on the effectiveness of acaricides for S. concavuscutum control. Therefore, this study aimed to evaluate the toxicity of acaricides registered for the control of A. guerreronis on S. concavuscutum, in addition to analysing the walking behaviour of tarsonemid mites when exposed to the products. The behaviour of mites exposed to acaricides was studied with a video-tracking system in choice and no-choice arenas treated with acaricides. The LC50 estimate for abamectin and fenpyroximate was 1.1 mg/L and 2757 mg/L, respectively. Azadirachtin, spirodiclofen and hexythiazox caused mortality of up to 25%. Only exposure to abamectin reduced the number of mites that reached the perianth and remained live, but no difference was observed in the number of eggs found at this site. No acaricide showed an ovicidal or sterilizing effect on the females. The total distance walked and the walking velocity were higher when S. concavuscutum was exposed to azadirachtin and lower when exposed to abamectin. All acaricides irritated S. concavuscutum; however, repellence was observed in only 5% of the tested population for abamectin and azadirachtin. Among the products recommended for the control of A. guerreronis, only abamectin showed potential in controlling S. concavuscutum.