Virulence And Infection Mechanism Of Entomopathogenic Nematodes To Two Ixodid Tick Species

Ticks are well known vectors transmitting a great variety of infectious pathogens and causing serious damage to human and livestock. In general, they arc controlled mainly with acaricides by means of plunge dips or spray races. Although acaricides have been effective in suppressing tick populations and incidences of tick-borne diseases, their main disadvantages have been the high costs, development of acaricide resistance in ticks, and environment pollution. To alleviate these problems, researches have been developing new methods of tick control, which not only can kill availably ticks, but are safe to environment. Consequently, non-chemical methods of tick control have received much recent attention and biological control of ticks is a popular option. Entomopathogcnic nematodes are excellent biological control agents. Numerous studies have demonstrate a high susceptibility of insects to entomopathogenic nematodes, but as yet little attention has been paid to their effect upon ticks.In the present study, a series of experiments were conduced on Dermacentor silvarum Olenev and Haemaphysalis longicornis Neumann, including efficacy of entomopathogenic nematode trains, susceptibility of tick species at various developmental stages, optimum concentration of nematodes, effects of nematode infection on fecundity of engorged female adults, changes of protein concentration and EST activity in tick hemolymph after nematode infection. The present results would provide important data for tick biocontrol by entomopathogenic nematodes in the future. The main results were as follows:1. The mortality of D, silvarum and H. longicornis adult ticks was recorded after their exposure in Petri dishes to 5 entomopathogenic nematode species. The species used were Steinernema carpocapsac BJ (Sc BJ) , NC32 (Sg NC32), Heterorhabdilis bacleriophora E-6-7 (Hb E-6-7), S.fcltiae Otio (Sf Otio), and S. ceratophorum D43 (Sc D43) . Engorged D. silvarum and H. longicornis female adults are killed readily by entomopathogenic nematodes, but their mortality differs among nematodes strains. The Sc BJ appeared to be the most pathogenic species for D. silvarum, the mortality of engorged females exposed to the nematode species for 14 days were 90%. Hb E-6-7 appeared to be the most pathogenic species for Hlongicornis, the mortality of engorged adult females exposed to the ncmatodc species for 14 days were 93.3%.2. The mortality of ticks varied significantly with nematode concentrations (1000-10000 infective juveniles per 6-cm-diamcter dish).7 The mortality of engorged female adults D. silvarum exposed to various concentration of the Sc BJ were 30.0% (1000 Us/dish), 85.0% (3000 Us/dish), 90.0% (5000 Us/dish), and 95.0% (7000-10000 Us/dish) respectively. 75.0% of engorged female adults //. longicornis were killed when exposed to 1000 Us/dish dose of the Hb E-6-7; 90.0% were killed by 3000 Us/dish nematodes; 95.0% were killed by 5000-10000 Us/dish nematodes.3. We measured tick fecundity by the number of eggs. The results showed significantly difference in the fecundity of D. silvarum and H. longicornis females between infected ticks and uninfected control ticks. At the concentration of 10000 Us/dish nematodes, the onset of laying eggs of H. longicornis females were later than uninfected control ticks.4. The hcmolymph protein level of H. longicornis feeding females infected by Hb E-6-7 changed greatly. After infection of 12 hours, the protein level in hemolymph of infected ticks increased sharply to its maxmum (92.21 μ,g/μl). The protein level in hcmolymph of infected ticks declined remarkably (49.06 μg/μl) at 24th hour, and declined its minmum (34.25 μg/μ1) at 48th hour. The proteins level of uninfected control were steady during experimental period.5. The EST activity in hemolymph of H, longicornis feeding females infected by Mb E-6-7 varied significantly. The EST activity of infected ticks was similar to that of uninfected control ticks from 0th hour to 12th hour. On the 24th hour, the EST activity of infected tick...