| The emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae),(=A. marcopoli Obenberger), is an important international quarantine insect pest. It mainlyattacks the ash trees (Fraxinus spp.)(Oleaceae). EAB larvae feed on the phloem, cambium, andsapwood under ash bark. It is very difficult to detect and control because of its highlyconcealed life characters. Recent years, EAB have caused more and more serious damages, andposed great threat to urban landscaping and forest development in China.At present, life history and biology of emerald ash borer have already been investigated indetail, but the key factors influencing its natural population development are still unsure.Therefore, in this study, the abiotic and biotic factors related to the EAB population densitieshave been surveyed and analyzed in different damage extent areas such as Tianjin City, BeijingCity and Liaoning Province from2010through2011in order to obtain the key factors, and toforecast the population developmental trend in the future. The main results were as follows:1. Ecological niches of EAB larvae and its natural enemies in Tianjin, Beijing andLiaoning areas were studied respectively. The results showed that the number of EAB larvaeand its natural enemies decreased gradually with the height of host trees, but the verticaldistribution ranges of EAB larvae and its natural enemies were different between different hosttrees, F. mandshurica and F. velutina. Distribution scope of EAB larvae and its natural enemieson F. velutina was wider than that on F. mandshurica. The following effects of varied naturalenemies to EAB larvae and their utilization on space and nutrition were also different. InTianjin area, both parasitoid Spathius agrili Yang (Hymenoptera: Braconidae) and predatorwoodpeckers had strong following effects to EAB larvae and thus showed intensivecompetition for space and nutrition. Woodpeckers revealed the strongest following effects to itsprey in Beijing. While the competition among mircroorganism, Metapelma sp.(Hymenoptera:Eupelmidae)and Spathius agrili was intense. In Liaoning, distribution scope of EAB larvae andits natural enemies was narrower than that in Beijing and Tianjin, so the following effects of natural enemies to host larvae were not apparent. But competition for space and nutrition werealso tense among different natural enemies.2. The EAB adult longevity, food consumption, oviposition and oviposition duration weredetermined by group rearing, couple rearing, and single female rearing without separation,single female rearing under visual separation and single female rearing under olfactoryseparation in laboratory. The results showed that separate rearing reduced the longevity andfecundity of EAB adults. The adult longevity and fecundity differed significantly (P<0.05)among different treatments, but there was no significant difference in oviposition (P>0.05). Noseparation for single female rearing gave the longest (32.40d), while group rearing caused theshortest average longevity (20.77d). The average longevity in the treatment of single femalerearing was longer than those in couple rearing and group rearing. For single female rearingtreatment, adults with visual separation consumed the maximum ash leaf (156.16mm2per day),while those with olfactory separation consumed (107.35mm2per day). No separation forsingle female rearing caused highest oviposition and the longest oviposition duration, whichwas98.33d and21.33d, respectively. It is concluded that block of intraspecific individualcommunications significantly influences the feeding, development and fecundity of EABadults, and olfactory plays the most important roles in intraspecific individual communicationsand vision follows. In addition, disturbance or competition among individuals may also havesome effects on the longevity and fecundity of EAB adults.3. Natural population life tables for EAB in three areas of Tianjin, Beijing and Liaoningwere constructed by specific time sampling method. The results indicated that populationquantity would increase for the three areas in the following years. And in Beijing the EABpopulation density had the fastest growing trend (I=12.9997), then in Tianjin (I=12.4388), andlast in Liaoning (I=3.6394). In addition, it was also illustrated that the parasitoid S. agrili(EIPC=1.5382and woodpecker (EIPC=1.4515) were the main lethal factors for EAB inTianjin and Beijing, respectively. But in Liaoning, the main lethal factors was resistance of hosttrees (EIPC=1.4029). 4. Abiotic and biotic factors of EAB natural population were studied by using theprincipal component analysis method. The results showed that host trees was the mostimportant factor related to EAB population densities. In addition, both annual extreme hightemperature and annual extreme low temperature were the main abiotic factors. Meanwhile,influence of host plant and its DBH on the number of EAB larvae was examined usingvariance analysis method. The results revealed that influence of host plant on the number ofEAB larvae differed significantly (F=37.011, P<0.0001), while there was no significantdifference in host trees DBH (F=1.414，P>0.05). And no interactive effect was found betweenhost plant and DBH (F=0.257, P>0.05).Through those investigations and studies, we got the following conclusions: the influencesof separation conditions on EAB population development were ascertained; life tables of EABnatural population in different damage areas were constructed successfully; the niches of EABand its main natural enemies in different areas were clarified; and the key factors influencingEAB natural population development were confirmed finally. These findings provide necessaryparameters and scientific supports for rational control of EAB. |
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