| Eotetranchus sexmaculatus(Riley),Oligonychus biharen(Hirst)and Eutetranychus orientalis(Klein)are three important pestiferous spider mites on rubber trees.Chemical control are the main strategy and widely used for the control of these three rubber tree spider mites.However,the chemical control has inherent disadvantages,such as insect resistance,pest resurgence and environmental pollution.Biological control can overcome these disadvantages.Neoseiulus barkeri(Hughes)is a widely used commercial predator mite for controlling spider mites.Additionally,Amblyseius largoensis(Muma)is the predominant predator mite found on rubber trees.To evaluate the efficiency of applying both introduced and native natural enemies for controlling rubber tree spider mites.This study evaluated the predatory efficiencies and prey preferences of N.barkeri and A.largoensis on three rubber tree spider mites.Also,the effects of prey density on cannibalism between two natural enemies and intraguild predations(IGP)of them were assessed.Additionally,the study analyzed the control efficiencies of N.barkeri alone and both predator mites together on three rubber tree spider mites using indoor and greenhouse experiments.The main results were as follows:1.The control efficiency of A.largoensis on three species of spider mitesThe functional responses of A.largoensis to the different stages of E.sexmaculatus,O.biharen and E.orientalis all matched Holling-II equation,but the predation efficiencies were different on different spider mite species.The predation capacity of A.largoensis against the larvae of three spider mites reached 347.92/d,409.48/d and 438.4/d,respectively.The control efficiencies of A.largoensis on the adults O.biharen,E.sexmaculatus and E.orientalis were the lowest,which are 2.83/d,35.41/d and 29.66/d,respectively.The order of control efficiencies on E.sexmaculatus is larva,protonymph,egg,deutonymph and adult.The order of control efficiencies on O.biharen is larva,protonymph,deutonymph,adult and egg.The order of control efficiencies on E.orientalis is larva,protonymph,deutonymph,egg and adult.2.The prey preferences of N.barkeri and A.largoensisThere were certain differences in the prey preferences of predators when facing different prey combinations.When there is no extraguild prey,N.barkeri prefers to prey on the eggs,larvae and nymphs of themselves,and the survival rates were 40.00%,80.00% and 53.33%,respectively.On the other hand,A.largoensis prefer to prey on eggs,larvae and nymphs of N.barkeri,and the survival rates were 13.33%,80.00% and 73.33%,respectively.When there were spider mites existing,the prey preference of A.largoensis depend on the species of spider mites.It preferred intraguild prey(survival rate 26.67%)when E.orientalis existed.When E.sexmaculatus or O.biharen existed,it preferred extraguild prey,and its preference on O.biharen was higher compared to E.sexmaculatus and E.orientalis.3.The effects of prey density on the cannibalism and IGP of N.barkeri and A.largoensisThe density of extraguild prey could significantly affect the cannibalism and IGP of N.barkeri and A.largoensis.When sufficient number of E.sexmaculatus existed,the largest decrease of N.barkeri cannibalism was observed,which was 68.85%.When sufficient number of O.biharen existed,the cannibalism of A.largoensis was smallest,it decreased 62.90%.For the IGP,the largest decrease of N.barkeri IGP was observed,when O.biharen existed,which was 80.00%.When E.sexmaculatus existed,the IGP of A.largoensis was smallest,it decreased 69.44%.However,the effect of E.orientalis density on the IGP of A.largoensis was relatively small.When E.orientalis existed,the IGP of A.largoensis decreased only 20.83%.4.The control efficiencies of applying both N.barkeri and A.largoensis together indoor and in greenhouseIndoor observation results showed that different combination of predator mites had different predatory abilities against E.sexmaculatus,O.biharen and E.orientalis.When one N.barkeri combined with three A.largoensis,the average daily predations of E.sexmaculatus,O.biharen and E.orientalis were 96.67,77.33 and 30.33,respectively.The predation ability here reached the highest compared to four N.barkeri,three N.barkeri combined with one A.largoensis,two N.barkeri combined with two A.largoensis,and four A.largoensis.In the greenhouse,the control efficiency of N.barkeri and A.largoensis with the ratio of 1:3 as well as the A.largoensis alone on O.biharen reached 87.11% on the 28 th day,which was significantly higher than the control efficiency of N.barkeri alone.5.Evaluation of the control efficiencies of N.barkeri on E.sexmaculatus in field6,000/plant,12,000/plant,and 18,000/plant of N.barkeri were released on the rubber trees.The control efficiencies on E.sexmaculatus on the seventh day after releasing reached 53.67%,54.85%,and 53.16%,respectively.On the 14 th day after releasing,the control efficiencies increased up to77.83% 、 60.38% and 69.00%,respectively.the control efficiencies of N.barkeri on three spider mites increased over time. |
