Studies on The Biology and Chemical Control of Amblyomma Variegatum (Fabricius, 1794) Ticks on The Accra Plains of Ghana

Abstract

In a study of the life cycle of Amblyomma variegatum under laboratory conditions of 72%±2 RH and temprature of 28°C±2, the feeding periods of larvae and nymphs on rabbits were 6-9 days and 6-13 days respectively, while that of adults on sheep was 17-19 days. The mean unfed weights of larva, nymph and adult were 0.149 x 10-3g, 0.906 X 10-3g and 28.5 x 10-3g respectively, while their mean fed weights were 2.14 x 10-3g, 48.6 x 10-3g and 2874 x 10-3g respectively. The moulting periods for larvae and nymphs were 14-19 days and 17-19 days respectively. Oviposition took an average of 26 days, with a range of 24-28 days. Saturated KCL and NaCL solutions with water as control were used to study the weight changes in and the laying pattern of ovipositing adult female A. variegatum ticks. Relative humidities of 83%±2, 72%±2 and 95%±2 were provided by saturated KCL and NaCL solutions and water respectively throughout the period of the experiment. Total number of eggs laid were 9,655 for KCL, 10,583 for NaCL and 5,074 for H20. Under these conditions, saturated NaCL solution appeared to provide the best favourable humidity conditions for the ovipositing Amblyomma variegatum tick. In a study to assess the sex of moulting nymphs,55 fed nymphs of Amblyomma variegatum were randomly selected and weighed. Nymphs which weighed above 0.059g resulted in adult females, while nymphs which weighed below 0.031 g resulted in adult males, with 0.031 g - 0.059g as area of overlap. In an experiment to look at the efficacy of some acaricides, Supamix, SteLadone , Lindane and Amitraz were assayed against fed and unfed larvae, nymphs and adults of Amblyomma variegatum. Based on their lethal concentrations (LC50), Supamix and Steladone placed first and second respectively in all the stages except at the unfed nymphal stage where Lindane led with LC50 of 0.001629, while Supamix and Steladone had LC50 of 0.001794 and 0.002258 respectively. Amitraz appeared not to be effective against all the stages since the percentage mortalities were less than 50% at the recommended concentration of 0.025, especially the larval stage where no mortality was recorded, even when the concentration was increased to 0.045 (almost twice the manufacturer's recommended concentration). It however, had a quick knock down effect on larvae and nymphs with the ticks recovering after 3 hours Lindane produced only 66% inhibition of oviposition of the laying females at the recommended concentration of 0.025, while Arnitraz had no inhibition at the recommended concentration. Supamix and Steladone showed 100% inhibition of oviposition at their recommended concentrations.