Influence of mating and age on susceptibility of the beetle Anoplophora glabripennis to the fungal pathogen Metarhizium brunneum

• Tested effect of beetle mating and age on susceptibility to a fungal pathogen.
• No evidence of immunosenescence was found in old Anoplophora glabripennis.
• Mating increased susceptibility of mature beetles to Metarhizium brunneum.
• Male beetles were more susceptible to M. brunneum prior to sexual maturation.

The age and life history of an insect can influence its susceptibility to pathogens. Reproduction can be costly and may trade off with immunity while it is generally assumed that immunity will decrease with increasing age through a process called immunosenescence. Fungal pathogens are used as biological control agents for a variety of insect pests, and Metarhizium brunneum is being developed to control the Asian longhorned beetle (Anoplophora glabripennis), an invasive wood-borer. Because adult female A. glabripennis take 1–2 weeks to mature after eclosion and both sexes can be long-lived, we investigated how age and mating status would influence susceptibility of A. glabripennis to M. brunneum. Young (6.5 day-old) unmated, mature (27–33 day-old) mated and unmated, and old (57–71 day-old) unmated and mated adults were inoculated with a lethal dose of M. brunneum. The presence of M. brunneum in the hemolymph was quantified and beetle mortality was monitored daily. There was a cost to reproduction for mated mature male and female beetles which died a median of 1.6–1.9 days earlier than unmated beetles, while there was no effect of mating on susceptibility for old beetles. We found no evidence for immunosenescence in old beetles, as they did not die faster than young or mature beetles. Young unmated males however were more susceptible than mature or old unmated males, while there was no effect of age on susceptibility of unmated females.

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