Abstract:

Objective: Massicus raddei is widely distributed in eastern Asia, but the insects only outbreak in regional oak forests in Jilin and Liaoning provinces of China. This study aims to ascertain potential effects of host plants with different preference levels on the spread and outbreak of M. raddei in China, so as to provide theoretical guidance for ecological management in outbreak regions and early warning in distribution-free regions. Method: A total of 137 distributional points of M. raddei in China were obtained based on literature, database search, and field investigation. Eight climate variables with correlation coefficients < |0.9| and relatively larger contribution rate to the potential distribution of M. raddei were screened out from 19 environmental variables downloaded from WorldClim between 1970 and 2000 by ArcGIS 10.0. Then the data were converted into the ASCII format data required for Maxent. Through database search and further artificial screening, 2 548 host distributional points of M. raddei were obtained in China. Based on the feeding preference degree of host species distributed in every counties of China, the suitability degrees of M. raddei in each county were assigned as specific values, and then the ASCII format data of risk map of hosts was obtained by using ArcGIS. In the MaxEnt model, two files of distribution points of M. raddei and environmental variables and two files of distribution points of M. raddei and the risk map of hosts were successively imported, and the average predictive results of repeated 10 runs by MaxEnt were regarded as the potential suitable areas of M. raddei based on only climate factors or host distribution, respectively. By applying ArcGIS, aforementioned two layers were overlapped to obtain a new potential distribution combining climate with host distribution, and then the precision of the three predicted models was all evaluated through actual distribution points obtained from field surveys. In the three predicted results, the habitat of M. raddei in China was divided into four categories: non-suitable areas, low suitable areas, moderate suitable areas, high suitable areas, according to the suitability index. Finally, the areas of regions of four suitability levels in three prediction results were calculated and plotted. Result: Under current climatic conditions, the high suitable areas of M. raddei were mainly concentrated in Jilin, Liaoning, Beijing, Hebei, Tianjin and northern Zhejiang, whereas the suitable areas failed in including some distribution points in Yunnan obtained from the field survey. Under the current host distribution, obvious distinction in host preference was observed between southern and northern China. Two susceptible hosts (Quercus mongolica and Q. wutaishanica) were distributed in the northern provinces, where the borer would show high suitability, whereas the secondary preferred hosts were mainly distributed in the southern provinces, accordingly, the borer would show low and moderate suitability. The potential distribution of M. raddei based on the combination of climatic and host factors would be more concordant with its actual distribution and infestation conditions, that is, the suitable area covers all distribution points obtained from field surveys. Most regions of China were climatically suitable for M. raddei except for Xinjiang autonomous region and Qinghai province. The total suitable areas were larger than those only based on climatic or host factors. Therein, the range of low and moderate suitable regions became wider and the range of high suitable regions reduced. Conclusion: Host species and distribution are the dominant ecological drivers which determine the suitability level of M. raddei. Both preferable host plants and suitable climate are potential ecological drivers which result in regional outbreak of M. raddei in northeastern China. In addition, all non-distribution areas of China are facing risks of spread and colonization of M. raddei.

Key words: Massicus raddei, maximum entropy model, susceptible hosts, regional outbreak, potential suitable distribution