Chemical control of Nysius natalensis Evans (Hemiptera: Orsillidae), a pest of sunflower in South Africa

Abstract

No insecticide is currently registered for Nysius natalensis Evans (Hemiptera: Orsillidae), control on sunflower [Helianthus annuus L. (Asteraceae)]. Field as well as laboratory trials were conducted to evaluate efficacy of insecticides for N. natalensis control. During budding prior to anthesis, insecticides were applied aerially. These were endosulfan, a mixture of dichlorvos + monocrotophos, mevinphos, a mixture of endosulfan + cypermethrin, methomyl and cypermethrin Compared to the untreated control, all insecticides provided effective control of N. natalensis. However, re-infestation by the pest occurred in all treatments after five days. A laboratory evaluation of the efficacy of the contact action of eleven insecticides in controlling N. natalensis adults on sunflower heads during application or immediately thereafter was conducted. Insecticides were representative of different groups and modes of action. These were carbosulfan, methomyl, endosulfan, demeton-S-methyl, dichlorvos, chlorpyrifos, malathion, profenofos, cypermethrin, fenvalerate and tau-fluvalinate. The insecticides were applied to sunflower heads containing 50 N. natalensis adults in plastic containers. All insecticides controlled N. natalensis effectively. The efficacy of the eleven insecticides against N. natalensis adults that re-infest sprayed fields from three hours post-application onward, were also evaluated. The insecticides were applied as full cover sprays to sunflower plants in the field. Disks were cut from the leaves three hours after treatment and placed in small plastic containers. Adults were transferred to the treated leaves and evaluated against those on leaves treated with water only. Fenvalerate and tau-fluvalinate were less effective in controlling N. natalensis than the other insecticides evaluated. Reduction in efficacy of seven of the insecticides was evaluated over a period of 14 days. Systemic insecticides remained more effective over longer periods than contact insecticides. However, the contact action of endosulfan remained as effective as the systemic insecticide, demeton-S-methyl. Endosulfan has a low toxicity to bees and will therefore control N. natalensis without a detrimental effect on pollination. To limit the number of applications, correct timing of insecticide application is important. The period that sunflower heads take to turn downward after completion of anthesis will determine the period for application of insecticides against N. natalensis during seed fill.