Innovative Control Methods for Amblyomma Variegatum (Fabricus, 1794), using Entomopathogenic Fungi, Beauveria Bassiana and Arhizium Anisopliae in Traps Baited with the Attraction-Aggregation-Attachment Pheromone

Abstract

Studies were commenced to investigate the potential use of the fungi, Beauveria bassiana and Metarhizium anisopliae and the attraction-aggregation-attachment pheromone (AAAP) for the control of Amblyomma variegatum. The objectives of the study were threefold: to determine the range of perception of the optimal dose of the pheromone with and without carbon-dioxide. in the field; to investigate if there were any synergistic or additive effects of B. bassiana and M anisopliae on A. variegatum; and to develop and test a device which could be used for pheromone delivery and infection of ticks by the fungi. The number of ticks that responded to AAAP in the laboratory decreased with decreasing doses of AAAP. The relation of the tick response to decreasing doses of AAAP was given by: r= 0.62, r2 = 0.39;, r=0.13, fl= 0.018 and r= 0.611, r2 =0.376 for males, females and nymphs respectively. For increasing doses of AAAP, tick responses were given by the relation r = 0.81, ?- = 0.066 and r = 0.58, r2 = 0.337 for males and females respectively. The nymphs showed a weak response to both decreasing and increasing doses of AAAP. When AAAP alone was used, a dose of 6.6mg attracted the highest number of adult ticks in the field from a distance of 4m but when 500g of CO2 was incorporated, more ticks were attracted to the AAAP and the range of attraction was increased to Sm. Upto 900/o of the released ticks within a radius of 4m were attracted to the combination of AAAP and CO2 within 3hrs while only 23% were attracted with AAAP alone within the same period. Reducing the weight of CO from 500g to 50g reduced the number of ticks attracted to AAAP and the number of ticks even reduced further when the weight of CO2 was reduced to 5g. These differences were significantly different at the 5% level. High soil temperature ranges, 3 I-52°C were found to reduce the attraction of ticks to the AAAP. The oil formulations of the separate and the mixture of fungi of a concentration of lx108 spores/ml, caused higher tick mortalities (sometimes as high as 100°/o) in the laboratory while that of the water formulation had less than 25% even at higher fungal concentrations. Tick mortalities were higher during the wet season (92%) compared. to the dry season when the highest mortality recorded was only 30% and these results were significantly different at the 5% level. The mixed fungi caused significantly higher tick mortalities compared to the separate fungi. Tick mortality increased with increasing fungal concentrations and the highest mortality was obtained with a concentration of lxl011 spores/ml in the field, while in the laboratory I 00°/o tick mortality was obtained with a fungal concentration of lxl 08 spores/ml and above. In the experiments to study any potential detrimental effects of AAAP to the fungi, the number of ticks killed due to fungal infection decreased when the amount of AAAP added to the fungi was increased but the differences were not significant at the 5% level. Tick mortality due to infection by lateral transfer of fungi occurred with the ratio of 1: 1 for exposed: non-exposed combination producing the highest tick mortality. There were significant differences between mortalities caused in long term exposure (24hrs) and short term exposure (30 minutes) with higher mortalities being observed in long term exposure. Tick mortalities took place irrespective of sex combinations. However, the overall efficiency of tick mortality due to fungal infection by lateral transfer was relatively low. The tick trap that was devised showed 790/o efficiency in mortality for ticks that were incubated in the laboratory and 66.3% for ticks that were left in the field after exposure to the mixed fungi and these results were significantly different at the 5% level. This technology could be improved and can be transferred to small scale famis where it can be incorporated with other Integrated tick Management (ITM) packages to help reduce A. variegatum populations in the field and also reduce losses due to heartwater, poor quality of animal products and improve the general economic gains for the farmers.