Forest tent caterpillar moth

Mature (pre-pupating) larvae are 2 to 2.5 inches (50 to 64 mm) in length. The caterpillars are black, dark brown, or gray, with broad blue longitudinal stripes and thin yellow stripes extending along each side. The back of each abdominal segment bears a white spot that is wider toward the head end. The sides are partially covered with fur-like long setae. == Biology ==

The forest tent caterpillar moth is nocturnal, taking flight soon after nightfall and returning to rest before dawn. It is not known how far an egg-laden female can fly, but there is one credible report of this species flying hundreds of kilometers with the assistance of an unusually strong wind. Trails of silk heavily loaded with pheromones secreted by other colony members induce larvae to move, while the close presence of other colony members brings them to quiescence. This indicates that there are social cues that are used to increase the locomotive efficiency of each individual larva. Pupation occurs after caterpillars reach a size threshold that is attained more quickly when caterpillars forage in groups. This is particularly important since delayed development to threshold increases the risks of predation and food depletion. However, as larvae proceed into the later instars, they become increasingly independent and by the fifth instar rarely form aggregations. This ontogenetic change in gregariousness results from an increase in the costs of maintaining grouping due to changes related to predation, thermoregulation, silk production, and foraging. Thermoregulation Forest tent caterpillars are ectotherms so they rely on sources of heat from the environment to raise their body temperatures. In order to do this, they bask together and benefit from group thermoregulation. Elevating body temperature is essential in increasing metabolic rates for movement and food processing, so proper thermoregulation leads to an increased rate of development. This is very important for M. distria caterpillars, which rely on fast growth in spite of low environmental temperatures to benefit from the high food quality and the smaller predation risk in the spring. Thus, it is an adaptive advantage to bask in groups. However, as caterpillars grow, thermoregulatory needs decrease and the benefit of group living is gradually overridden by other factors such as food competition. == Behavior ==

Foraging Eating times are variable. Foraging trips can occur at any time and are very coordinated: either the entire colony forages or no one does. A small proportion of starved individuals is enough to reach agreement and start group movement. With age, competition for food becomes more important, especially as resources become scarce. Grouping decreases growth rate via a decrease in food intake so ontogenetic changes toward more mobility and independence can be viewed as simple "scaling" relationships between caterpillars and food sources evolved to increase the benefits of individual foraging in later stages. In addition to this, making silk is more costly for larvae in their first instars, so grouping is beneficial in earlier stages. As caterpillars develop, they decrease the use of shared silk. In order to position himself, the male moves backwards and bends his abdomen towards the female, pushing the tip towards the female's bursa copulatrix. There is a significant positive correlation between the body sizes of copulating pairs, which indicates that mating is not random with respect to size, presumably because of male-male competition for larger females. Whatever the cause, outbreak densities give rise to cyclic population dynamics, characterized by highest fecundity at peak population density and reduced fecundity for several generations during decline. At low population densities, moths are found mating high above the ground, in the forest canopy. Offspring pass the winter inside their eggs. Although cold tolerant, they are susceptible to freezing in extreme cold temperatures, with the risk of mortality varying seasonally with changes in temperature and physiology. Predation Individual risk is lower in larger groups due to collective defense from predators, the dilution effect, and the selfish herd theory. All of these effects provide supplementary protection to individuals in the middle of the group. To compensate for group conspicuousness, caterpillars minimize movement, reducing their chances of being located by invertebrate predators. This behavior has associated costs because it decreases individual caterpillars’ selectiveness regarding food sources, as they will not be able to work to get better food sources. Caterpillar grouping behaviors change depending on food source; on less favorable food sources, caterpillar groups tend to splinter, thereby potentially increasing the risk for predation. Ontogenetic changes in caterpillars reduce the risk of predation and as a consequence, predation-related benefits of group foraging decrease with time. Moreover, grouping in later instars has the extra cost of an increased risk of pathogen transmission. Maryland and New York (state). Furia crustosa is now classed as a synonym of Furia gastropachae. The species of fungus rarely infects species outside the genus Malacosoma. In 2002, Resting spores were observed even within the cadavers infected by other resting spores, a phenomenon not previously observed among the Entomophthorales. This allows the fungus to initiate cycles of secondary infection via conidia'. Also, host infection by resting spores was highest at intermediate levels of soil moisture. Infection of fourth instar larvae by resting spores and conidia was maximized at cooler temperatures (of 10 to 20 °C). == Outbreaks ==

The caterpillars are considered a problem when the larva population explodes in the spring. They can completely consume the foliage of a tree. Trees usually recover from this, refoliating within a month and resuming photosynthesis. Under most circumstances, little lasting damage is caused to the trees; however, the disappearance of foliage is considered to be an unattractive nuisance. On those rare occasions when infestations last for three years or more, tree mortality rates can become significant. Multiple outbreaks in Northern Ontario, Canada, in the 1990s resulted in over six consecutive years of aspen defoliation in some areas. One outbreak in upstate New York and Vermont began in 2002, with 650,000 acres (2600 km²) defoliated in New York and 230,000 acres (930 km²) in Vermont by 2005. The cause of the outbreak cycle is not known with certainty. There are a large number of natural mortality agents which could be responsible for population cycling, including parasitoids, predators, starvation, disease, and severe weather; however these "cycles" vary tremendously and unpredictably in intensity. Most infestations subside after one or two years as a result of a combination of these factors. The most common parasitoids associated with population decline are flies of the families Tachinidae and Sarcophagidae. Forest tent caterpillar outbreaks in Canada generally tend to recur every decade or so, but with the precise interval varying significantly at finer spatial scales. Outbreaks usually last two to four years, but are often as brief as a single year. Although the insect's distributional range is quite large, the area over which decadal outbreak cycles are synchronized (i.e. oscillating with the same phase) varies substantially. Outbreak cycles are more strongly periodic and synchronized in eastern Canada than in western Canada. Where spatially separated populations are phase-synchronized, the synchronization may be due to the process of entrainment, as conjectured by Moran's theorem. However, it has been argued on one occasion that extensive outbreaks are the result of a positive feedback loop on population growth rates - a nonlinear dynamic that is more consistent with catastrophe theory. == References ==