The Role of Predators , Parasitoids and Pathogens in Regulating Natural Populations of the Non-parasitic Stages of Rhipicephalus Appendiculatus Neumann and other Livestock Ticks, and Related Aspects of the Ticks' Ecology

Abstract

Natural enemies of the important ticks in Kenya were studied with a view to assessing their role in regulating natural populations, and their possible use in biological control of ticks. Predators of engorged females of Rhipicephalus appendiculatus and Amblyomma variegatum in the field were found to be rodents, ants, spiders, birds, lizards and shrews. In the field there was about 43% predation of R· appendiculatus females, 46% of A· variegatum females and 36% of engorged R.appendiculatus nymphs. Death due to environmental factors did not exceed 7% for any group while predation contributed by small animals was 7% . Domestic chickens were found to be effective tick control agents in a cattle boma where they ate 86% of engorged ticks put out there. These results have shown that the effect of predators should not be ignored in making a computer model for R· appendiculatus • .. A hymenopteran parasi toid resembled Hunterellus hookeri and Ixodiphagus texanus in some aspects, and differing in other aspects was found in A· variegatum nymphs from the Trans-Mara area, infesting 49% of 463 nymphs collected over a period of one year. This is the first record of a parasitoid of A· variegatum. The parasitoid was however not found in nymphs of A· variegatum from Rusinga Island. A 40% infestation of A· variegatum of unfed nymphs was achieved in the laboratory when the ratio of parasitoids to nymphs was 1: 3. The bacteria Proteus mirabilis, Pseudomonas sp. and Serratia marcescens were isolated from engorged ticks which had been in the grass for 8 days, causing about 10% mort ality, while laboratory colonies were infected with Enterobacter cloacae, Escherischia coli and Staphylococcus aureus. Only 1% of 484 ticks were fo und to be infected with fungi; Mucor sp., Fusarium sp. and Aspergillus sp. Experimental infections of adult R· appendiculatus with Beauveria bassiana and Metarhizium anisopliae resulted in 73% and 30% mortalities respectively Engorged females of R· appendiculatus were found to have a d r opping off rhythm , with about 71% of them dropping between 0600 and 1000 hours, while 66% of the engorged nymphs dropped off between 1400 and 1800 hours . There was no definite rhythm of drop-off for larvae however. The dropoff rhythm in females a nd nymphs was not affected by feeding on tick-sensitised animals or by their time of application on animals . Onset of drop-off was delayed by 24 hours in both cases. These results indicate that delaying animals in the cattle boma until 1000 hours and bringing them in at around 1600 hours would allow most engorged ticks to drop in unfavourable places, and this procedure would therefore be useful in an integrated tick management package.