Pine caterpillar Dendrolimus is a collective term for insects of the genus Pine caterpillar in the family Lepidoptera leafless moths. Also known as caterpillars, fire caterpillars, ancient called pine silkworms, there are more than 30 species, China has 27 species of distribution, is the most abundant pine caterpillar species of countries. It is an important tree species such as pine and cypress. The earliest Chinese record is found in the Guangdong Chronicle of Longchuan County in 1530: "In the ninth year of Ming Jiajing, when there was a great drought, it occurred year after year, the hair was black, the pine leaves were exhausted, and the cocoon pine branches were exhausted, and the end of winter was exhausted." "To this day, pine caterpillars are still the main forest pests with large occurrence and wide range of harms among forest pests.
Pine caterpillars occur in an annual age that varies greatly depending on the species and climatic conditions. However, from the perspective of molecular biology, the mechanism of infestation of pine caterpillars has been less explored, which limits our in-depth understanding of the internal molecular mechanisms of its infestation. Therefore, it is urgent to explore the infestation mechanism of pine caterpillar from its own genetic and genomic perspectives in order to form a more effective sustainable control system.
Larch caterpillars complete 1 generation in 2 years or 1 year in northeast China, and 1 generation in the Altai Forest Area of Xinjiang spans 3 years, with larvae overwintering twice and larval stages up to 22 months.
Akatsuki caterpillar and alpine pine caterpillar are one generation a year. Dechang pine caterpillars are 1 to 2 generations a year. Yunnan pine caterpillars are produced once a year at high altitudes and 2 generations a year at low altitudes.
Cypress pine caterpillars are 2 generations a year.
Oil pine caterpillars are produced in northeast China, 1 to 2 generations a year in Beijing, and 2 to 3 generations a year in Sichuan.
Simao pine caterpillars are 1 to 3 generations a year.
Wenshan pine caterpillars are 2 generations a year.
Pinus massoniana is produced in 2 generations a year in the Yellow and Huai River Basins, 2 to 3 generations a year in the Yangtze River Basin, and 4 generations a year in Guangdong and southern Guangxi.
The further south the distribution, the more generations there are. In the same region, although the number of generations occurring each year is relatively fixed, the percentage of 1 to 2 generations, 2 to 3 generations, and 3 to 4 generations per year is not the same. This is mainly related to temperature, light, pine tree growth and the degree of damage. Generational differentiation generally manifests itself when the larvae move from 4 to 5 years. Different species of pine caterpillars, regardless of generation, have roughly similar living habits.
lay eggs
Female moths mostly lay eggs on pine needles, in the form of blocks, each female moth lays 200 to 800 eggs, generally 300 to 500 grains, and the highest egg production of Yunnan pine caterpillars is as high as more than 1700 grains. The larvae hatch at 6 to 9 a.m., and the hatching larvae are more concentrated before the 3rd instar, have the habit of spitting and drooping, spread by wind, disperse after 3 instars, and have a total of 6 to 9 instar larvae, and overwinter with 3-5 instar larvae.
wintering
South of the Yangtze River, except for the overwintering trees under the Simao pine caterpillar in high altitude areas, the young pine needle bush is generally used as the wintering place. Large trees overwinter in parts in the bark layer of the trunk of large trees. In the Yellow River and Huai River basins, the red pine caterpillar and masson pine caterpillar mostly overwinter in the trunk bark layer, and some overwinter in the canopy coniferous bushes. In North China, the oil pine caterpillar winters under the bark or under the ground stones, and the larch caterpillars in the northeast overwinter below the ground cover. The larvae feed the most at the last age, accounting for 70 to 80% of the total larvae. Mature larvae pupate in cocoons on branches, in coniferous bushes or on ground cover shrubs, and venomous hairs on and off the body of old mature larvae. Adults mostly feather in the evening, and the tail and egg laying are carried out at night, tending to lay eggs in the growing pine forest. Adult flying migration is the main way of spreading, and the distance of flight is related to the topography, pine forest distribution, degree of damage, and light source.
Pine caterpillar occurrence areas can generally be divided into frequently affected areas, occasional disaster areas, and non-disaster areas. Most of the disaster areas are distributed in large areas of pure forest. Masson pine caterpillars are infested, mostly in low hilly areas below 500 meters above sea level. Yunnan pine caterpillar and Dechang pine caterpillar occur rampantly in mountainous areas of 500 to 1000 meters. The infested area of Wenshan pine caterpillar can reach up to 1200 meters. The damage range of larch caterpillar is relatively wide, and in natural forest areas, the height of the disaster area can reach 2000 meters. In the natural ecological environment, several major pine caterpillars have the law of periodic rampant infestation. The length of the rampant cycle is closely related to geographical distribution, generation number, natural enemy resources, topography, forest type, quantity and quality of food, vegetation conditions and climatic conditions in forest areas. In general, the interval between the annual occurrence of many generations of Pinus massoniana is short, about 3 to 4 years, and the outbreak of 1 generation of Red Pine Caterpillar occurs about 10 years or so. Pinus tabula flare erupts in the 2nd to 3rd generation zone and occurs about 3 to 5 years.
Pine caterpillars can only accumulate in numbers and gradually develop into rampant infestations when environmental conditions are particularly favourable to it. This first, most suitable niche is called the base of occurrence. Pest occurrence bases are variable and often change or form new bases as trees grow, harvest, renew, and alternate. Under nutrient-rich conditions, the larvae grow robustly, the adult body length, the wingspan increases, the female-male ratio, pupal length, pupal weight, egg laying, generational differentiation ratio, etc. are conducive to offspring proliferation. Malnutrition can at least cause an increase in the male ratio, a decrease in pupal weight, and a decrease in egg production, a difference of more than double. Outbreak zones often cause fasting deaths due to inadequate food intake. Climate not only directly affects the distribution and generational size of pine caterpillars, but also affects the dynamic balance between the entire biological population, thus inducing intermittent cycles and quantitative changes. Under the conditions of sufficient light and heat, the growth and development period is shortened; in the case of unsuitable climate, it can cause a large number of pine caterpillar deaths. During prolonged drought, the internal moisture of the host plant decreases and the sugar content increases, which can increase the feeding amount of the larvae and indirectly promote the increase in the reproduction of the pest. Short-term storms can wash away the larvae on trees, while prolonged rains can affect the cocooning, pupae and feathering of the larvae. There are more than 300 species of natural enemies in each stage of pine caterpillar. Among the parasitic insects, the parasitic rates of pine caterpillar red-eyed bees, pine caterpillar black egg bees, flat-bellied wasps, pine caterpillar black lateral grooves, pine caterpillar ridge cocoon bees, umbrella skirt chase parasitic flies, silkworm belly parasitic flies, and pine caterpillar narrow-cheeked parasitic flies have the highest parasitic rates; among predatory insects, black mountain ants and double-needle ants prey the most. Among the pathogenic microorganisms are albicans, mass polykeratovirus, and nuclear polykeratovirus. Among the birds, the large cuckoo, dark gray crane, yellow oriole, gray magpie, large and so on have a large predation.