The Forest Tent Caterpillar, Malacosoma disstria Hubner

The forest tent caterpillar (FTC), Malacosoma disstria Hubner, is the most widely distributed indigenous tent caterpillar in North America (Furniss and Carolin 1977). FTC has been recognized as an important defoliator of a wide variety of deciduous hardwood trees throughout its range for many years (Batzer and Morris 1978). Although this univoltine insect is called a tent caterpillar, it is unlike other Malacosoma species in that the larvae do not construct tents. Instead, FTC spin silken mats on the trunks and large branches where they congregate to molt or rest from feeding. Larvae also deposit silk in strands along which they travel to and from feeding sites. The caterpillars themselves are relatively harmless to people (i.e., they do not bite or sting) although a few people have an allergic reaction to handling them. Populations of FTC occasionally or periodically attain outbreak proportions. During outbreaks, enormous numbers of caterpillars cause widespread and extensive defoliation of host trees, and may create an overwhelming nuisance to people encountering them. Except in southwest Alabama and southern Louisiana where abundant populations recur annually on water tupelo, Nyssa aquatica L. (Batzer and Morris 1978), FTC is elsewhere considered as one of the cyclical outbreak species among forest Lepidoptera (Myers 1993). Populations of FTC characteristically fluctuate between extremes on a somewhat regular schedule, typically increasing to outbreak proportions every 6-16 years (Myers 1993; USDA Forest Service 1996). Outbreaks usually subside after 2 to 4 years of heavy defoliation, but have persisted for up to 6 years (USDA Forest Service 1996). Seldom are trees killed during such outbreaks and where tree mortality has occurred, it usually has not been substantial (Anderson 1960). Severe and repeated defoliation can, however, lead to dieback and/or reduced growth of affected trees, which in some instances may be significant (Drooz 1985). One of the earliest documented FTC outbreaks in Florida occurred in Citrus and Marion counties during the Aprils of 1965 through 1967. The outbreak was noted as widespread ( ca. 30,000 ac ), causing very heavy defoliation of turkey oaks (Quercus laevis Walter) and a “great problem” due to the abundance of crawling caterpillars. Other large FTC outbreaks in Florida have been recorded in Pasco Co. ( 1967; ca 2,000 affected acres; primary host turkey oak), Citrus and Hernando counties (1969; ca 10,000 ac of the Withlacoochee State Forest; turkey oak), Hernando, Marion and Pasco counties (late March to April 1977; ca. 25,000 acres; turkey oak), and Hernando, Lafayette, Levy and Pasco counties (1988; Quercus spp.) (FDACS-DPI and DOF records). More recently, outbreak populations of FTC and its associated problems have reached unprecedented heights in West Central Florida. Noticeable levels of defoliation were first reported in portions of Polk and Hillsborough counties on water oak (Quercus nigra L.), laurel oak (Q. laurifolia Michaux), and live oak (Q. virginiana Miller), during the spring of 1993. Outbreaks of FTC have since developed on the same hosts in many of the surrounding areas of Citrus, DeSoto, Hardee, Hernando, Highlands, Lake, Manatee, Pasco, Pinellas, Orange, Osceola, and Sarasota counties. The extent, magnitude and impact of this outbreak reached pronounced levels in 1995 and, in general, escalated to alarming proportions in 1997. Noticeable declines in FTC populations were, however, recently evident at some locales where caterpillars had been abundant for 3-4 years. Although no tree mortality has occurred as a direct result of defoliation, the sheer number of caterpillars, their frass, and the subsequent populations of adult moths have caused numerous problems for people, particularly in urban environments.