Observations on the Oak Twig Pruner, Anelaphus villosus (Coleoptera: Cerambycidae), in Michigan: Size of Twigs Pruned, Insect Survival, and Seasonality of Twig Drop

The oak twig pruner [OTP; Anelaphus villosus (Fabricius)] is likely a species complex, with A. parallelus (Newman) recently recognized as a synonym. The parallelus form of A. villosus is considered the subject of this paper. In Michigan, OTP has a 2-year life cycle, with twigs pruned primarily in even-numbered years and adults emerging from the fallen twigs in odd-numbered years. During 1990 to 2011, I studied various aspects of OTP life history in southern Michigan (Ingham County). Based on measurements from over 300 infested oak twigs, they averaged 43.1 cm long, 9.4 mm in diameter at the pruned end, weighed 22.9 g (dry weight of woody material), and had 57 leaves. OTP adults emerged in 1991 from 15.9% of 290 pruned twigs that had fallen in 1990 and were left on the forest floor until December 1990 and then placed in individual sleeve cages and later reared indoors in early 1991. Likely parasitoids of OTP emerged from 15.5% of these same 290 twigs. No linear relationship was found between the dry weight of OTP adults and the size or weight of the twigs in which they developed. During inspections along the same 1-km-long forest path from 1994 to 2011, recently-fallen pruned twigs were only found in even-numbered years, usually starting in late May to early June, peaking between late June to mid-July, and ending between August to December. The annual number of pruned twigs found along this same 1-km section of trail, varied from a low of 24 twigs in 2004 to a high of 168 in 2006. For all years combined, 89% of the recently fallen infested twigs collected on the ground in June had green foliage, compared with 52% of the twigs collected in July, 7.3% in August, and 2.6% in September.