In-gallery social behaviors of the ambrosia beetle, Xylosandrus germanus (Coleoptera: Curculionidae)

The east Asian ambrosia beetle Xylosandrus germanus (Blanford) was first detected in the United States in 1932. It now occurs across much of eastern North America and parts of the Pacific Northwest. It attacks a broad range of stressed, woody hosts including ornamental and orchard species. The foundress tunnels into the sapwood of hosts where it cultures a symbiotic fungus as food for its offspring. A few other ambrosia beetles have been shown to possess a facultatively eusocial structure among gallery members, but this has not been described for Xylosandrus spp. Using a novel artificial diet arena, we quantified the behaviors of X. germanus larvae and adults (foundress and mature offspring) over 10 wk inside their galleries. Foundresses were responsible for constructing the gallery. They also initially tended the fungal garden and brood but eventually spent most of their time blocking the gallery entrance. Larvae were mainly observed to feed, crawl, or be inactive within the gallery, regardless of the absence or presence of adult siblings. Adult female offspring were primarily inactive, likely due to dormancy. Adult male offspring actively crawled and attempted to mate with their sisters before eventually dispersing out of the gallery. Cooperative hygienic behaviors (removal of frass, cannibalism of dead nest mates, grooming siblings) were observed but a division of labor among offspring was not clear. Rather, foundress behaviors were mostly distinct from offspring behaviors, particularly as the gallery aged. Because no overlap in generations occurred, X. germanus displays a quasisocial structure.

Development and reproduction of the foxglove aphid (Hemiptera: Aphididae) on invasive swallow-worts (Vincetoxicum spp.)

The foxglove aphid, Aulacorthum solani (Kaltenbach), recently was documented using the invasive species pale and black swallow-wort (Vincetoxicum rossicum (Kleopow) Barbar. and V. nigrum (L.) Moench, respectively) as host plants. Because these are new host plant records for this polyphagous species, we investigated foxglove aphid development and reproduction on pale and black swallow-wort relative to a known crop host, potato (Solanum tuberosum L.), at a 25:20°C thermophase and a photoperiod of 16:8 (L:D) h. Almost no such data have been previously reported for a noneconomic host plant. Larval development and survival, as well as adult reproductive development and fecundity, were similar between the two swallow-wort species and potato. Adult aphids lived significantly longer on pale swallow-wort than the other two host plants, but this extended longevity encompassed the postreproductive stage. Foxglove aphid population parameters were therefore similar among the three plant species as well as most previous reports on crop plants. Pale and black swallow-wort appear to be suitable secondary hosts for foxglove aphid; other factors possibly limit aphid abundance on these two plant species in the field.

Phytotoxicity of antofine from invasive swallow-worts

Pale swallow-wort (Vincetoxicum rossicum) and black swallow-wort (V. nigrum) are two emerging invasive plant species in the northeastern United States and southeastern Canada that have shown rapid population expansion over the past 20 years. Using bioassay-guided fractionation, the known phytochemical phenanthroindolizidine alkaloid, (-)-antofine, was identified as a potent phytotoxin in roots, leaves, and seeds of both swallow-wort species. In seedling bioassays, (-)-antofine, at μM concentrations, resulted in greatly reduced root growth of Asclepias tuberosa, A. syriaca, and Apocynum cannabinum, three related, native plant species typically found in habitats where large stands of swallow-wort are present. In contrast, antofine exhibited moderate activity against lettuce, and it had little effect on germination and root growth of either black or pale swallow-wort. In disk diffusion assays, antifungal activity was observed at 10 μg and 100 μg, while antibacterial activity was seen only at the higher level. Although both swallow-wort species display multiple growth and reproductive characteristics that may play an important role in their invasiveness, the presence of the highly bioactive phytochemical (-)-antofine in root and seed tissues indicates a potential allelopathic role in swallow-worts' invasiveness.