Bruce Spanworm Moths Typically Mate Near the End of Twigs in an Upside Down Position
Total Page：16
File Type：pdf, Size：1020Kb
Bruce Spanworm Moths Bob Armstrong The young caterpillars go through about five growth changes called instars or molts. Early in their growth the caterpillars are a pale yellow color. Later they may change to a dark olive or brown color with conspicuous lines along their body. This caterpillar period may last from 5 to 7 weeks. During this time they feed openly on the leaves or within the shelter of a leaf they have loosely rolled together with silk they can produce. By living, feed- ing, and growing inside a rolled leaf they are less conspicuous to predators. However, some birds, such as chickadees have learned to target these rolled up leaves. Bruce spanworm moths typically mate near the end of twigs in an upside down position. Eventually the caterpillars lower themselves to the ground, usually on a thread of silk they produce. Have you ever wondered about the numer- They then pupate within thin silken cocoons they ous moths you see flying about at night in make in the soil or in the moss under the trees and late fall and even into early winter when bushes. Studies have shown that wind can disperse there is snow on the ground? You are most the very young larvae, hanging from their silken likely seeing male Bruce spanworm moths (Op- threads, quite long distances up to about one-half erophtera bruceata). The males are seeking the mile. This certainly helps the wingless females dis- wingless females that typically crawl up to the tips perse to other areas. of bushes or the base of a tree and emit phero- The adults emerge from the pupal stage in late mones in hopes of attracting a male for mating. fall to begin the cycle again. Typically the males Flying and mating in late fall and early winter has emerge one to two days before the females. the advantage of fewer insect eating birds being One trick to find the wingless females is to look for around. Also, this mating ritual occurs under the bushes or trees with a lot of defoliation. They seem cover of darkness which further decreases the to really target blueberry bushes in the Juneau chances of being eaten. area. So find an area where the leaves have been Most female moths have wings. So what would obviously eaten or chewed upon. Wait until you be the advantage of being wingless? I can think of see male moths flying about. Then visit these defo- a few: the females don’t have to expend energy, liated areas in early darkness. With a headlamp it is get hit by cars, can produce more eggs (being too pretty easy to locate the mating moths by looking heavy to fly is not important), they are close to the carefully at all the ones with wings and you may bushes and trees that their young need to feed on, see one mating with a wingless female. and they don’t have to travel far to lay their eggs. As caterpillars they can do a lot of defoliating to After mating, the females crawl into the bark crev- their host bushes and trees. This can cause prob- ices or other protected areas of the tree or into the lems with the plants, especially over the short moss at the base of the bush or tree to lay their term. eggs. The eggs are laid in late fall and early winter Of interest is some studies have shown that the and remain dormant until the following spring. defoliation by Bruce spanworms on blueberries The eggs typically hatch in late spring when the may, over the long run, actually benefit the plants. leaves of the bushes and trees that the caterpil- It appears that the caterpillars’ poop (technically lars (larvae) feed upon have started to grow. If cool called frass) provides more nutrients than the de- weather delays the growth of the leaves the young composing leaves and the blueberry plants actually larvae will bore through the buds to feed on the do better in the long run. soft tissues within the bud. The male Bruce spanworm moth typically flies at night in search of females. This is a female Bruce spanworm moth waiting at the end of a blueberry branch for a male to find her. The eggs of the Bruce spanworm are quite tiny, less than 1 mm in diameter. When their caterpillars first come out they are a pale yellow color. The caterpillars often lower themselves on silk As the caterpillars grow they turn a darker color and form thread that they produce. At this time they stripes along their body. can be easily distributed long distances by the wind. Bruce spanworm caterpillars provide good food for birds such as this Chestnut-backed Chickadee. The Bruce spanworm pupae start out a golden brown or green, becoming a dark gray-brown as the adult develops. For More Information Brown CE. 1962. The life history and dispersal of the Bruce spanworm, Operophtera bruceata (Hulst) (Lepidoptera: Geometridae). The Canadian Entomologist 94: 1103-7. Eidt, D. C.; Embree, D. G.; Smith, C. C. 1966. Distinguishing adults of the winter moth Operophtera brumata (L.), and Bruce spanworm O. bruceata (Hulst) (Lepidoptera: Geometridae). Canadian Entomologist 98: 258-261. Fitzpatrick, S. M.; Troubridge, J. T.; Peterson, B. 1991. Distribution of European winter moth, Operophtera brumata (L.), and Bruce spanworm, O. bruceata (Hulst), in the lower Fraser Valley, British Columbia. Journal of the Entomological Society of British Columbia 88: 39-45. Htbert C, St-Antoine L. 1999. Oviposition Trap to sample eggs of Operophtera bruceata (Lepidoptera: Geometridae) and other wingless geometrid species. The Canadian Entomologist 131: 557 - 565 Walther-Toews, David, 2013. The origin of feces: what excrement tells us about evolution, ecology and a sustainable society. ECW Press, Toronto, Ontario, 200 pp. Marden, J.H. 1995. Evolutionary adaptation of contractile performance in muscle of ectothermic winter-flying moths. The Journal of Experimental Biology 198, 2087–2094 Mols, C.M.M. and M.E. Visser 2002. Great tits can reduce caterpillar damage in apple orchards. Journal of Applied Ecology 39: 888-899. Weiss, M.R. 2006. Defecation behavior and ecology of insects. Annu. Rev. Entomol. 51: 635-61.