Optimizing modes of inoculation of Rhipicephalus ticks (Acari: Ixodidae) with a mitosporic entomopathogenic fungus in the laboratory

The process of strain selection is an important step in the development of insect pathogens for biological control. Bioassays were conducted in the laboratory to evaluate the efficacy of different methods of inoculation using Rhipicephalus pulchellus Gerstäcker (Acari: Ixodidae) as a model. Initially, an oil-based formulation of Metarhizium anisopliae (Metsch.) Sorok. (Ascomycota: Hypocreales) titred at 10(9) conidia ml(-1) was applied to R. pulchellus adults using a Burgerjon spray tower or a microapplicator. Inoculation by microapplicator yielded poor results (25.0% tick mortality) compared to Burgerjon's spray tower (52.3% tick mortality), although the mean number of fungal conidia on R. pulchellus adults was lower (1.5 x 10(4) +/- 1.1 x 10(3) conidia ml(-1)) after spraying by Burgerjon's spray tower compared to 1 x 10(6) conidia ml(-1) obtained with the microapplicator. Thus, inoculation by Burgerjon's spray tower was selected for further investigations. Different modes of inoculation were tested and included direct spray of inoculum on the tick and substrate (SS), direct spray on the substrate and tick followed by transfer of the tick to clean uncontaminated Petri dish (SP) or indirect inoculation of ticks through substrate (SW). The LC(50) values following contamination of nymphs (LC(50) = 1.4 x 10(7) conidia ml(-1)) and adults (LC(50) = 6.7 x 10(7) conidia ml(-1)) in SS were significantly lower compared to SP; nymphs (LC(50) = 5.7 x 10(8) conidia ml(-1)) and adults (LC(50) = 5.3 x 10(9) conidia ml(-1)) and SW; nymphs (LC(50) = 5 x 10(8) conidia ml(-1)). Although the LC(50) value in SS was the lowest, it recorded the highest tick mortality among control ticks (24.2% at 2 weeks post-treatment) and (23.3% at 3 weeks post-treatment) in nymphs and adults respectively compared to SP (2.5 and 5.8%, respectively) and SW (0.0 and 0.0). Results show that among the modes of inoculation tested, SP was the most appropriate for inoculating R. pulchellus adults. SW and SP were identified as appropriate techniques for infecting the R. pulchellus nymphs with conidia formulated in oil.

In vitro investigation of the toxic effects of extracts of Allium sativum bulbs on adults of Hyalomma marginatum rufipes and Rhipicephalus pulchellus

The toxic effects of the extracts of Allium sativum (Garlic) were evaluated against adults of Hyalomma marginatum rufipes and Rhipicephalus pulchellus using three types (Types A, B and C) of contact toxicity bioassays. A. sativum bulbs were extracted with acetone, ethanol and dichloromethane (DCM) solvents. Among these three solvents, it is the DCM extract of A. sativum that appears to have anti-tick activity. In the Type A contact toxicity bioassay, DCM extracts of A. sativum demonstrated a high acaricidal bioactivity against H. m. rufipes with 100 % of ticks killed in less than an hour, and toxicity persisted to the second day. A weak acaricidal activity of aqueous extracts of A. sativum was observed in the Type B contact toxicity bioassay. In the Type C contact toxicity bioassay, a concentration of 24 % w/v of DCM extracts of garlic in sunflower oil (Helianthus annuus) had killed 100% of H. m. rufipes (LC50= 5.9 % w/v) and R. pulchellus (LC50 = 10.3 % w/v) by 24 hours post-treatment of ticks. The results obtained from this study suggest that DCM extract of A. sativum is a potential source of novel acaricidal agents.