Evaluation of the interaction between beauveria bassiana and an aphicide for the management of the tobacco aphid myzus persicae nicotianae.

Abstract

Aphids (Myzus persicae nicotianae) cause damage by sucking sap from the plants leading to distortion and wilting of the foliage, and eventually reducing economic yields. In order to minimise losses to viral diseases, it is important to use insecticides in association with fungi to control insect pests in an environmental and ecological friendly way without contaminating the environment. A study was carried out from October, 2013 at Kutsaga Research Station in the laboratory to evaluate the efficacy of Beauveria bassiana (contact insecticide)and imidacloprid (systemic insecticide) 200 SL for the control of tobacco aphid, Myzus persicae nicotianae. Three doses of 200 SL Imidacloprid (Imida) namely: Imida low rate 0.55 ml per 500ml water (LR); Imida medium rate 1.1 ml per 500ml water (MR) and Imida high rate (2.2 ml per 500ml water (HR) were mixed with Broadband® Beauveria bassiana (B. Bass) at three different rates namely: B. bass 4 x 103 (LR); B. bass.4 x 104 (MR) or B. bass 4 x 105 (HR) to evaluate the most effective application combination rate of Beauveria bassiana and imidacloprid for the control of the tobacco aphid. Treatments were: water (control); Imida MR; B. bass MR; B. bass LR + Imida LR; B. bass LR + Imida MR; B. bass LR + Imida HR; B. bass MR + Imida LR; B. Bass MR + Imida MR; B. Bass MR + Imida HR; B. Bass HR + Imida LR; B. Bass HR + Imida MR and B. Bass HR + Imida HR. Inoculation of aphids was done and data collected from day 1 to day 7 after inoculation. Mortality of aphids was recorded at 8 o’clock in the morning cumulatively as a percentage of the initial number infested (10 per petri dish). Results showed that there were significantly high p<0.001 cumulative mortality from B. Bass HR + Imida HR and B. Bass HR + Imida MR in comparison with the control and other treatments. The number of deaths on day one indicated clearly that the level of mortality was dose-dependent and the presence of the contact insecticide (Beauveria bassiana) compared with systemic insecticide (imidacloprid) which took three days to show mortality. In Imida MR death rates started at day 3 and accumulated up to 98% at day 7 whilst B. Bass started at day 1. However, death in day 1 increased as the dosage of B. Bass increased. It was also evident that as the rates of B. Bass and Imida increased the cumulative mortality also increased significantly (p<0.001). For controlling aphids B. bass HR + Imida MR was the best because its efficacy was the same as B. bass HR + Imida HR showing the same mortality in day one and by day five, both mortality had reached 100%.