Host plant resistance among tomato accessions to the spider mite Tetranychus evansi in Kenya.

The spider mite Tetranychus evansi has a broad range of host plants. Control of T. evansi has been a big challenge to tomato farmers due to its fast rate of reproduction, development of resistance to chemical pesticides and its ability to use weeds as alternative hosts when the tomato plants are not available. The aim of the current study was to determine the host plant acceptance and the relative contributions of trichomes in the control of the red spider mite by comparing the survival, development and oviposition rates of the red spider mite on eight tomato accessions. Leaflets from eight tomato varieties were assayed with the spider mites to determine the egg laying capacity and developmental time of the spider mites on the tomato accessions as well as the trichome densities. Densities of trichome types I, IV, V and VI varied among the tomato accessions. Variation in types I, IV and VI accounted for most of the variation in mite responses. The varieties with high densities of types IV and VI had the highest fecundity and mite development did not go beyond the larval stage. The developmental time varied significantly among the tomato accessions. The results indicated that the higher the density of trichome type I the lower the adult survival. The findings indicated possible resistance of some of the tested tomato accessions against T. evansi which is partially associated with trichomes types and density.

Attraction response of adult Rhipicephalus appendiculatus and Rhipicephalus pulchellus (Acari: Ixodidae) ticks to extracts from Calpurnia aurea (Fabaceae).

Experiments were carried out to investigate the response of two tick species Rhipicephalus pulchellus Gerstaker, 1873 and Rhipicephalus appendiculatus Neumann, 1901 to three different extracts (acetone, aqueous and oil) of the dried leaves of Calpurnia aurea (Aiton) Benth in both an inverted glass tube and a dual choice T-olfactometer. The oil extract at 50 and 100mg/ml attracted 46.7% and 65.9% of R. appendiculatus, respectively, in the inverted glass tube assay, which was comparable to 47.8% of the attraction-aggregation-attachment pheromone (AAAP) used as positive control. At a dose of 100mg/ml the oil extract attracted 52.4% of R. pulchellus in the T-olfactometer bioassay. The relative attraction of both tick species to plant extract was also tested in semi-field plot experiments using a trap baited with different concentrations of emulsifiable extract of C. aurea. A dose of 100mg/ml attracted 52.2% of R. pulchellus and 44.4% of R. appendiculatus from a distance of 1m while 14.4% of R. pulchellus and 12.2% of R. appendiculatus were attracted from 5m distance at the same dose. Addition of CO(2) to the plant extract-baited-trap at the dose of 100mg/ml increased the range of attraction of adult R. pulchellus (44.4% from 5m distance) and up to 33.3% of adult R. appendiculatus tick from a distance of 4m. The results of this study suggest that extracts from C. aurea can potentially be used as baits in a trap for the control of ticks in the field.

Performance of a prototype baited-trap in attracting and infecting the tick Amblyomma variegatum (Acari: Ixodidae) in field experiments.

Investigations were commenced to study the potential use of the fungi, Beauveria bassiana, Metarhizium anisopliae, and the attraction-aggregation-attachment pheromone (AAAP) for the control of Ambloyomma variegatum as an environmentally friendly technology. The objective of the study was to develop and test a device, which could be used for pheromone and carbon dioxide delivery and infection of ticks with the fungi in an attempt to control the tick populations in the vegetation. Using a pheromone-baited device treated with the fungi mixture, 79% of the ticks released were attracted and exposed to the fungi and of these, 78% died during incubation in the laboratory. In another set of experiments, of the released ticks that were similarly exposed to fungi using the pheromone-baited device and left in the vegetation, 33.8% were recovered compared to recoveries of between 76 and 84% in the controls. These results were significantly different at the 5% level, an indication that the pheromone/fungi mixtures had significant effect in reducing the tick population in the field.

Effects of combining the fungi Beauveria bassiana and Metarhizium anisopliae on the mortality of the tick Amblyomma variegatum (ixodidae) in relation to seasonal changes.

The effect of formulation, fungal concentration, type and seasonal changes on the mortality of the tick Amblyomma variegatum was investigated. A previous study demonstrated high pathogenicity of strains of the fungi Beauveria bassiana and Metarhizium anisopliae against the ticks Rhipicephalus appendiculatus and Amblyomma variegatum (Kaaya et al. J Invertebr Pathol 1996; 67: 15-20). The present study was undertaken to explore possible additive or synergistic effects of the two fungi on A. variegatum. The effects of oil and water formulations at different concentrations of each fungus and combination of the two on the mortality of A. variegatum in the laboratory and in the field during the wet and dry seasons were determined and compared. The oil formulation performed better in all assays, with highest tick mortality of 92% occurring during the wet season at conidia concentration of 1 x 10(10) conidia/ml of the mixed fungi compared to 49% for the water formulation at similar conidia concentration. However, at the same conidial concentration during the dry season, mortalities in the field were relatively low with the mixture of the fungi recording 24% and 17% tick mortality for the oil and water formulation respectively. The effect of infecting the ticks with a cocktail of the two fungi was inconclusive under more controlled conditions in the laboratory but field results under both wet and dry seasons indicated significant differences between the separate and mixed fungi infections. The results demonstrate a potential of cocktail formulations in the control of ticks and possibly of other arthropod pests.

Attraction of Amblyomma variegatum (ticks) to the attraction-aggregation-attachment-pheromone with or without carbon dioxide.

The responses of adult Amblyomma variegatum ticks released from various distances to different doses of the synthetic attraction-aggregation-attachment pheromone (AAAP) (made up of orthonitrophenol, methyl salicylate and nonanoic acid in paraffin oil), dispensed from the center of circular field plots, were studied in the presence or absence of elevated levels of CO2. Up to 90% of the ticks released were attracted to the pheromone source in the presence of CO2 within 3h. CO2 alone was unattractive, similar to previous findings in Zimbabwe, but unlike results from a Caribbean A. variegatum population, which was significantly attracted to this signal. In the absence of CO2, smaller but significant proportions of the released ticks were attracted to the pheromone, albeit more slowly, suggesting another variation in the responses of this bont tick to inter- and intra-specific signals. Our results are interpreted in the light of a study undertaken elsewhere demonstrating relatively high heterozygosity among tick populations. Possible directions of further research to explore the use of the pheromone in off-host control of the tick are also highlighted.