Phenology, voltinism and brood development of Xylosandrus (Coleoptera: Curculionidae) ambrosia beetles in New York

Authors: Milbrath, Lindsey; Biazzo, Jeromy

Submitted to: Journal of Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2024
Publication Date: 10/18/2024
Citation: Milbrath, L.R., Biazzo, J. 2024. Phenology, voltinism and brood development of Xylosandrus (Coleoptera: Curculionidae) ambrosia beetles in New York. Journal of Insect Science. Vol. 24, Issue 5. https://doi.org/10.1093/jisesa/ieae102.
DOI: https://doi.org/10.1093/jisesa/ieae102

Interpretive Summary: Various ambrosia beetles are introduced pests of ornamental and orchard trees, including the black stem borer (Xylosandrus germanus) and granulate ambrosia beetle (X. crassiusculus). They bore tunnels or galleries into the sapwood of stressed trees where they grow symbiotic fungi to feed their offspring. Preventing attacks is preferred by growers but difficult to achieve. Biological studies may help identify different avenues or timing of control once attacks have already occurred. We conducted outdoor rearing and laboratory studies to better understand the timing of key points in the life cycle of the two beetle species. The black stem borer produces two and a partial third summer generation every year, and adults fly from mid-April to late September to start new galleries. For both species, the symbiotic fungus grows within a few days. Eggs are laid soon after and as long as the fungus is present. The lag between beetle colonization and reproduction is too brief to be exploited for management. However, disruption of other stages in gallery development may be useful for minimizing damage if attacks cannot be prevented.

Technical Abstract: The ambrosia beetles Xylosandrus germanus (Blanford) and X. crassiusculus (Motschulsky) are non-native pests in orchards and nurseries in North America. They construct galleries in the sapwood of stressed woody hosts and culture a symbiotic fungus as food for their offspring. Preventing attacks is preferred but a better understanding of their biology may elucidate additional avenues for control. Recent phenological studies are lacking for X. germanus that is common in New York, and biological information on brood and gallery development is lacking for the less abundant X. crassiusculus. We conducted both outdoor rearing and laboratory studies to better understand the timing of key events in the maturation of their galleries, particularly associated with the symbiotic fungi. Two and a partial third summer generation were consistently observed over two years for X. germanus, and thus three flights of adult females (foundresses) occurred each summer from mid-April to late September. In both the field and laboratory, initial growth of the symbiotic fungus occurs within a few days of gallery initiation. The rapid development of the reproductive tract and oviposition of X. germanus appears to be stimulated by the presence of the fungus. Fungal, reproductive, and brood development are similar for the related X. crassiusculus in laboratory studies; the two species mainly appear to differ in size. The lag between beetle colonization and reproduction is too brief to be exploited for management. Disruption of other events involved in gallery development may be useful for minimizing damage if attacks cannot be prevented.