Spatial distribution pattern of Endoclita signifier larvae infestation on Eucalyptus.

Endoclita signifier is a new borer pest which has caused serious damages to introduced Eucalyptus species in Guangxi and Guangdong provinces in recent years. We applied six indexes of distribution and geo-statistical methods to analyze the spatial characteristics of the damages to Eucalyptus by larvae E. signifier. The analysis of distribution indexes showed that the spatial distribution pattern of E. signifier larvae was aggregated. The geo-statistical analysis indicated that, at small scale of plantations, the spatial distribution pattern was aggregated at slight, moderate and serious infestations, and the distances of spatial dependence of E. signifier larvae were 20.00,40.38 and 69.42 m, respectively. The degree of spatial dependence decreased with the increase of infestation. The E. signifier larvae had no aggregation characteristics in the plots. The larvae bored into the same stem through independent tunnels without connections. The larvae could attack each other while two or more larvae were collected from their host stem tunnels and put together in one container. The aggregation of the larvae at small scales is due to the synergistic effects from exterior environment of the larvae population and the oviposition characteristics of adults. At provincial scale, the spatial distribution pattern was random at slight infestation, and aggregated at moderate and serious infestations. The distance of spatial dependence of the pest was 43.60, 15.50 and 12.47 km, respectively at slight, moderate and serious infestations. The degree of spatial dependence increased with the increase of infestation, and the degree of aggregation of E. signifier larvae was related to the distribution and age of Eucalyptus plantations. Eucalyptus plantations are widely distributed in every county of Guangxi Province, and the slightly infested plantations were scattered with random spatial distribution pattern. The moderately and seriously infested plantations were mainly distributed in central and southern areas of Guangxi Province where Eucalyptus were planted early, and currently most of the plantations were 2nd generation of sprout. After this native insect shifted its host to exotic Eucalyptus successfully, it infested more seriously in the 2nd generation plantations than in the 1st generation plantations and showed an aggregated spatial distribution pattern.