| The apple buprestid, Agrilus mali Matsumura (Coleoptera: Buprestidae), is a devastatingborer of apple trees (Malus spp.). The damage is caused by larvae as they bore in the phloemand the cambium, with serious infestations, dieback of branches can be led, and even death ofthe whole tree. In1995, A. mali was found in Xinyuan, Yili, Xinjiang Uygur AutonomousRegion, attacking the endangered Xinjiang wild apple Malus sieversii (Ledeb.) Roem, the soleancestor of nowadays cultivars of the apple Malus domestica. After nearly20years of spread,40%of the Xinjiang wild apple forest, over3866.67hm2stand was damaged, and another666.67hm2stand has dead. Agrilus mali has became the primary threat of M. sieversii. For thelarvae living under the bark, insecticide are hard to contact, consequently, biocontroltechnologies were researched, and the results are as fallowed:1. Field survey of A. mali life history has been executed. Results indicated that, A. malihas one generation annually in Xinjiang, and overwinters in larval stage. Pupating takes placein mid May, till in mid August. Emerging begins in late May, and the adults appear about10days later. Oviposition begins in mid June and lasted in three months. In late June, the firstgeneration larvae begins to hatch, and in November they go into overwintering period. Thisresults are mainly consistent with previous studies, but all four stages of A. mali appear earlierand last longer, which means that its development is more irregular than the previous studies.2. Distribution patterns of A. mali larvae has been researched by field survey. At15subquadrats in Gongliu and Xinyuan,150M. sieversii were checked and all of them weredamaged in different degrees. Generally, the wild apple forests of Xinyuan were damaged moreseriously than Gongliu, and the tree grows at higher altitudes or closer to the water sourceusally suffered less. The populations of A. mali were counted by surveyed branches in differentways (i.e. the branch direction, the branching height, the damage degree and the branchdiameter measured for each larval gallery). It showed that the larvae distributions at different directions and heights has no significant difference, but populations in the branch with76～100%dead leaves, are significant less than other three damage degrees of branches (percentageof dead leaves:0～25%,26～50%,51～75%), and81.78%of larvae distribute on the branchwith20～55mm diameter. In addition, three calculating methods of A. mali population havebeen concluded, to meet different case.3. Determination of A. mali larval instars was studied. The larvae were sampledperiodically in forest, and the eggs were collected to hatch the first instar larvae. Threecharacteristics (i.e. peristoma width, urogomphus length and body length) were measured.According to the Dyar’s law, the data was managed with frequency analysis, and examined byone-way ANOVA method, Crosby ratio and checked with molting larvae, A. mali larva hasbeen divided into five instars, and all three determination characteristics are effective exceptbody length.4. Population limiting factors of A. mali were surveyed in Gongliu and Xinyuan.11species of natural enemies and3other factors were found. They totally caused67.66%and68.57%mortality of A. mali in Gongliu and Xinyuan respectively. The parasitoid waspAtanycolus denigrator (Hymenoptera: Braconidae) is the dominant natural enemy, caused19.10%and12.00%parasitization in Gongliu and Xinyuan respectively, Pyemotes sp. takessecond place, caused6.30%and10.13%parasitization in Gongliu and Xinyuan respectively.5. Biological habits of Pyemotes sp.(Acariformes: Pyemotidae) were researched. Resultsshowed that the mite has strong reproductive capacity. Its reproductive modes is viviparity, andits generation cycle is about7days, each female mite can produce87.5female progenies and5.5male progenies in average. Requirements of reproductive condition for this mite is easy tosatisfy. Its host selection range is wide, and the larvae of wasps are the best. Using Pyemotes sp.to control A. mali with indoor test, the highest parasitization gets47.83%. According to theresearch, Pyemotes sp. is a promising natural enemy, attaching with its wind dispersal ability,the application prospect of Pyemotes sp. is bright. 6. Four species of bethylid wasp, i. e., Sclerodermus pupariae, S. guani and another twospecies in the genus Sclerodermus,were applied under five different releasing ratio (0.5:1,1:1,2:1,4:1,8:1)(parasitoid number: host number) by bagging. Results showed that, after30d, allof the four parasitoids are effective, and the best is S. pupariae, making A. mali65.56%rectified reducing rate at ratio of8:1. After investigating the population of A. mali, S. pupariaehas been released directly on the damaged M. sieversii with the5ratio, and checked after30d,45d, and60d. The results showed that, the reducing rate is not only increasing as the timegoes by, but also increased by the higher releasing ratio. The best treatment is using8:1releasing ratio for60d, making A. mali50.97%rectified reducing rate. This result showed that,S. pupariae is an excellent parasitoid of A. mali. Combined with other natural limiting factors,A. mali would be completely controlled.7. Color traps were tested with different patterns of color and setting mode to learn ofattraction of A. mali adults. Results indicated that, the color of yellow and white aresignificantly more attractive than red, pink, blue, light blue, green, purple, grey and black; trapshanging in north are significantly more effective than the others; traps hanging at4m heightare significantly better than those hanging in2.5m height. The best board caught46A. maliadults during20days testing, which was lower than the expectation, the color traps still need toimprove.Through these surveys and researches, A. mali life history, larval instars and damageregulation has cleared; three calculating methods of A. mali population have been concluded;technique of using parasitoid S. pupariae to control A. mali in the forest stands was summarize;population limiting factors of A. mali had been mastered; color traps for adult were tested. Atlast the integrated management measures for A. mali were recommended. |
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