| Tetranychus cinnabarinus (Boisduval), which is widely distributed in China and the world, can harm many crops, vegetables and flowers, such as Zea mays, Solanum melongena and Hydrangea macrophylla. At present, chemical measures are widely used to control the mite. However, a series of problems such as resistance, residue and resurgence are increasingly serious. Bio-control is the important content of controlling the mites. It is reported that there are rich natural enemy resources of T. cinnabarinus. In this paper, the dominant natural enemy insects were evaluated, and their controlling effect against T. cinnabarinus was studied. The major results obtained are as follows.1. Evaluation of dominant natural enemy insects preying on T. cinnabarinusThe species and population dynamics of natural enemy insects preying on T. cinnabarinus on Hydrangea macrophylla, Solanum melongena and Zea mays were investigated, and the dominant species were evaluated with dominance index. The results showed that the species of natural enemy insects and dominant species were different on three species of host plants. Stethorus punctillum, Scolothrips takahashii, Acaroltes sp. and Oligota sp. were found on H.macrophulla, and the first two species were dominant natural enemies. S. takahashii, Orius minutus, Acaroletes sp. and S. punctillum were found on S. melongena, and S. takahashii was dominant. There were 3 species of natural enemy insects on Z. mays, S. punctillum, S. takahashii and Acaroletes sp., and S. punctillum was the dominant natural enemy insects. The daily preying capacity of adult and larva of natural enemy insects to adult, nymph, larva and egg of T. cinnabarinus were determined. Meanwhile, the relative disparity-sum method was introduced to evaluate natural enemy insects. The result showed that S. punctillum and O. minutus were dominant natural enemy insects of T. cinnabarinus.2. Functional responses and searching efficiency of dominant natural enemy insects to T. cinnabarinusThe predation functional response of O. minutus, S. punctillum and S. takahashii on the adult of T. cinnabarinus were studied. It was found that the functional response of 3 species of natural enemy insects were all belonged to Holling-Ⅱtypes, and the disc equations were Na=0.8420N0 /(1+0.0121N0), Na=07181N0 /(1+0.01757N0) and Na=0.5168NN0 /(1+0.0136N0) respectively. The values of Na max and a'/Th obtained by the disc equations showed that O. minutus had the strongest control to T. cinnabarinus and S. punctillum followed.By further analysis on the disc equations obtained, searching efficiency of 3 species natural enemy insects to T. cinnabarinus was studied. The results showed that searching efficiency models of O. minutus, S. punctillum and S. takahashii were S=0.8420/(1+0.8420·0.0144·Ng), S=0.7181/(1+0.7181·0.0243·N0) and S=0.5168/(1+0.5168·0.0262·N0) respectively. The searching efficiency of natural enemy insects declined gradually with the increase of T. cinnabarinus density. The optimum searching densities of 3 species natural enemy insects were simulated by the functional response moded of Holling-Ⅲtype. The results suggested that the mathematical models of optimum searching efficiency of O. minutus, S. punctillum and S. takahashii were Na=49.87·exp(-25.18/N0),Na=31.78·exp(-21.29/N0) and Na=26.59·exp(-22.40/N0), and therefore concluded that the ratio of natural enemy insects and pests can be 1:25,1:21 and 1:22 as a references, respectively.3. Starvation tolerance of dominant natural enemy insects and influence of starvation and spatial dimension on their predationThe starvation tolerance of dominant natural enemy insects, S. punctillum, O. minutus and S. takahashii, was examined by leaf disc test. The results showed that all of them had strong abilities of tolerating starvation, and they can survive for 96 hours,80 hours and 64 hours respectively under the condition of no preying completely. With the prolongation of starvation times, the survival rates of 3 natural enemy insects all decreased.The influence of starvation on predatory functional responses, preying capacities and predation rates of O. minutus, S. punctillum and S. takahashii were studied. The functional responses of 3 species natural enemy insects on various ranges of starvation to adult mites of T. cinnabarinus were all fitted to HollingⅡ-types. The functional response types of natural enemy adults were not altered by starvation duration within a certain range. The predation in 24 hours of natural enemy insects starved for 72 hours were concentrated in the first 12 hours of the test, especially in the first 4 hours, and natural enemy insects had fastest predation rates in this period. While the predation of natural enemies unstarved allotted in whole period of the test, and the predation rates changed slightly. The effect of spatial dimension on predation of adults O. minutus, S. punctillum and S. takahashii was studied with the petri-dishes of different sizes. Both preying capacity and predation rates of 3 species natural enemy insects decreased with the increase of the petri-dishes diameters. The predation of O. minutus and S. takahashii were appreciably affected by spatial dimension, while S. punctillum was less affected.4. Interspecific and intraspecific mutual interference and competition of dominant natural enemy insectsInterspecific and intraspecific mutual interference and competition of adults O. minutus, 5. punctillum and S. takahashii were studied. The results indicated that the predation efficiency of 3 natural enemy insects on T. cinnabarinus reduced gradually along with the density increase of natural enemy insects themselves. The interspecific mutual interference had more influence on predation than the intraspecific mutual interference did among 3 natural enemy insects. With the increase of natural enemy densities, both interspecific and intraspecific competition strength increased.5. Selectivity of natural enemy insects to host plantsSelectivity of adults O. minutus, S. punctillum and S. takahashii to host leaves was studied. The results showed that O. minutus had highest selective rates to S. melongena leaves, and S. punctillum demonstrated the best preference to Hydrangea macrophylla and Zea mays leaves. Selective rates of S. takahashii to Hydrangea macrophylla and S. melongena leaves were obviously higher than that of other leaves.6. Study on biological characteristics of S. takahashiiWith the feeding container made of concave slides, the predation behavior and development duration of S. takahashii were studied. The results showed that the predation process of S. takahashii to the mites included approaching, exploring, swooping, predation, throwing off and cleaning, and so on. The developmental periods of 2nd,3rd and 4th nymph of S.takahashii at 28℃were 1.8 d,0.9 d and 0.9 d respectively. |
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