The tree-of-heaven trunk weevil, Eucryptorrhynchus brandti (Harold) (Coleoptera: Curculionidae), is one of the most harmful pests that damage the tree of heaven, Ailanthus altissima Swingle (Sapindales: Simaroubaceae). Aggregation behavior tests of E. brandti adults were conducted in laboratory conditions. The effects of temperature and light on the aggregation behavior of adults were tested, and the effect of sex and host was conducted with binomial choice experiments. The results showed that (1) the adults aggregate in both light and dark environments but preferred the dark environment, (2) temperature can drive the aggregation of E. brandti adults, (3) host plants could trigger E. brandti adults’ aggregation behavior, which is probably related to phytochemicals and insect feeding and localization, (4) there was mutual attraction of males and females and chemical attraction of crude intestinal extracts of males and females, and (5) aggregation behavior of E. brandti adults may also be related to the mediating of physical signals in insects. In this study, aggregation behavior can help us understand conspecific interactions and discover some strategies for effective control.

Dormancy is important for overwintering insects to resist and adapt to adverse conditions. Dormancy generally contains quiescence and diapause. Eucryptorrhynchus brandti Harold (Coleoptera: Curculionidae), tree-of-heaven trunk weevil (TTW), is a destructive pest and highly host-specific to Ailanthus altissima in China. TTW has one generation per year and overwinters as both larvae and adults. In this study, to examined dormancy type of adults and find a method to store overwintering adults, we collected adults from 20 October 2018 to 13 March 2019. We studied the behavior and reproductive development of adults under field cold conditions for 0 and 10 d and laboratory warm conditions for 5 and 10 d. We recorded developing eggs in females, and the clarity of the testis edge, the yellow point in the testis lobe, the ratio of the inner content in the accessory gland, and the accessory gland color in males. Adults transferred from the field to the laboratory had resumed reproductive development directly. Results indicated that the dormancy type of TTW adults was quiescence. Adults stored in the field were still in a dormant state and the field-storage method was effective. Current study provided basic data for controlling overwintering TTW adults and solve the storage of insect sources during the winter.

Eucryptorrhynchus scrobiculatus (Motschulsky) (Coleoptera: Curculionidae) is a notorious pest of Ailanthus altissima (Mill.) Swingle (Sapindales: Simaroubaceae). E. scrobiculatus adults typically aggregate under leaves and in soil crevices at the base of A. altissima in the field. We hypothesize that the environmental factors and conspecific signals determine their aggregation behavior. To test this, we investigated adult numbers in light-exposed and shaded areas of the sample trees and conducted experiments in both field and lab settings. Results revealed that (i) greater adult distribution in shaded areas; (ii) significant influence of temperature and illumination on aggregation tendency in the field; (iii) no gender-based difference in aggregation degree and maximum aggregation between light and dark; (iv) the host plant triggering the aggregation tendency, negatively affected in the absence; (v) the aggregation tendency of E. scrobiculatus weakened with the temperature gradually changing to ordinary temperature; and (vi) mutual attraction and chemical attraction between males and females. Thus, the aggregation behavior was influenced by factors including temperature, light intensity, host plant, and conspecific signals, but light’s role was not obvious in the lab.