| As an ancient social insects, termites formed a unique immune mechanism in evolution synergy with nature. Termites have individual physiological immune strategy, but also they can greatly enhance their resistance for the control of pathogen depending on camp group life. Reticulitermes chinensis Shyder is a serious insect pest of houses and buildings, which is widely distributed in China. R. chinensis always exists in group of small and scattered, with a series of characteristics as strong disease resistance, difficult to control etc. Metarhizium anisopliae is a species of insect entomogenous fungi. It possesses broad application prospects in view of its various advantages including:wide host range, strong pathogenicity, safety for higher animal and crop. Hence, from the angle of the comparison of the termite individual physiological immune with group behaviors defense, this paper focuses on the research of group resistance and its mechanism of R. chinensis infected by M. anisopliae. The main results are as follows:1. Metarhizium anisopliae toxic effect on Reticulitermes chinensisTermites were divided into three densities (1heads/dish,10heads/dish,20heads/dish, respectively.Φ=9cm) after being infected by high concentrations of fungal conidia (1.0x107spores/ml). In4th days of infection, the mortality of termites in1heads/dish and10heads/dish were significantly higher than that of termites in20heads/dish, but there was no significantly different between the former two densities on the mortality. In8th days of infection, the mortality of termites has showed significantly difference within three density above. Moreover, the greater density of termites, the mortality is smaller. The same case happened in12th days of infection as the8th days. With the extension of the infection time, the mortalities of termites with three densities were rising.For the termites of three densities, the LC50after4days being infected by M. anisopliae were greater than that both after8days and12days. Under the same time of treatment, the bigger of the population density, the greater of LC50value, i.e. LC50(1heads/dish)<LC50(10heads/dish)<LC50(20heads/dish). The result showed that the greater the population of termites, the stronger of its resistance. 2. Infection effect of M. anisopliae on groups and the individual of termitesUnder scanning electron microscope, we found that the number of spores on the surface of termites presented a significantly change between groups (20heads/dish) and the individual (1heads/dish) of termites after infected by M. anisopliae. From lhour to12hours,24hours after termites inoculated with conidias of M.anisopliae, we found that the number of spores on individual termite’surface didn’t reduce obviously with the time going while it lessened significantly in groups of termites In addition, it was almost not observe the spores on the surface of individuals living in groups of termites after24hours.3. The role of hygienic behaviors of termites in resistance to M. anisopliaeThe behavioral relationship between termites had greatly strengthen when they were infected by M.anisopliae, which embodies two aspects as follows:allogrooming frequency and trophallaxis frequency, both of them had a significant increase. Mutual allogrooming frequency and trophallaxis frequency between two infected termites had a greater increase than both two Tween80-treated termites and both two completely untreated termites (control). Also, mutual allogrooming frequency and trophallaxis frequency between two Tween80-treated termites showed no significant difference with both two completely control termites. Meanwhile, the whole frequency of mutual allogrooming and trophallaxis in two infected termites had a greaterly higher than two Tween80-treated termites and two control termites, but there was no significant difference between the latter two experimental groups.In addition to the allogrooming duration of both two infected termites showed a obvious difference with two Tween80-treated termites. There wasn’t found clearly difference and regularity in other experimental groups in terms of mutual allogrooming duration. Comparing mutual trophallaxis duration in all treatment groups of termites, we obstained a result that mutual trophallaxis duration of one infected termite with one untreated termite in the same dish, which presented a greatly longer than two Tween80-treated termites and two completely control termites. However, the duration of mutual trophallaxis between two termites in other experimental groups had no dramatically difference with each other. In the mean time, we dindn’t discover the difference within two infected termites, two Tween80-treated termites and two completely control termites in the gross duration of mutual allogrooming and trophallaxis. We infer that the time of hygienic behaviors in termites, which sustains unstably and there isn’t clearly regular.4. Antibacterial activity of group and individual termites infected by M. anisopliaeThe3rd day testing found that the antibacterial activity generated by individual termites was the strongest and significantly higher than the group termites after infected by lower concentrations of M. anisopliae and other experimental termites. Although other experimental termites had generated some antibacterial activity, the difference was not significant. And the analysis result of the5th day was the same with the3rd day.5. Activity changes of protective enzymes in termites infected by M. anisopliaeFrom the activity of protective enzymes in group termites and individual termites after infected by lower dose of M. anisopliae spores, we can find that there was no significant difference between group-infected termites and their control groups on the activity of CAT, SOD, AKP and ACP. But the activity of CAT and AKP in individual termites were significantly higher than that in their control group, while no significant difference in individual termites on the activity of SOD and ACP.6. Expression changes of immune genes in termites infected by M. anisopliaeBy fluorescence qPCR assay, we found that termicin and transferrin significantly upregulated in individual infected termites, and significantly higher than that in individual comparison termites, group infected termites and group comparison termites. What’s more, the relative expression of termcin in individual comparison termites was higher than that of group comparison termites. Similarly, the relative expression of transferrin in individual comparison termites was significantly higher than that in group infected termites. Yet there was no significant difference between other two groups. |
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