For temperatures below the starting point of development, various pests exhibit different cold-resistance capabilities. Generally below 8°C, the body's metabolism slows down, life activities decrease, and it enters a cold coma (also known as hibernation). If it takes a long time, it will lead to death. Cryogenic death is generally below 0°C but usually does not exceed minus 15°C.
The low temperature has a close relationship with the lethal efficacy of pests and the length of time for maintaining low temperatures. Generally, maintaining a low temperature for a long time will have a strong lethal effect. For example, the adult sawtooth will die in thirteen days at a temperature as low as minus 5°C, but it will not be able to completely die for sixty-seven days at 5°C; its larvae will have to die for twelve days at minus 5°C. However, at 5°C, it takes 45 days to completely die.
Temperature also affects pest growth and population density. Usually within a suitable temperature range, the higher the temperature, the faster the growth and development of the parasite, and thus the temperature determines the length of the period of activity of the pest throughout the year, but also indirectly affect the algebra and population density of the full-year development, as well as the damage of the article .
The response and adaptability of pests to temperature are not only different depending on the species, but also affected by the following conditions.
(1) The speed of temperature change. Rapidly rising or falling temperatures often make it difficult for pests to adapt, thereby reducing the tolerance for high or low temperatures.
(2) Changes in atmospheric humidity. The favorable or unfavorable temperature range of pests also changes with changes in atmospheric humidity. In general, pests are more tolerant to temperature changes than dry conditions under dry conditions.
(3) The duration of adverse temperature. A prolonged period of unfavorable temperatures can lead to the death of pests.
(4) Different physiological conditions and developmental stages have special requirements for temperature. The response of pests to temperature is related to their intrinsic physiological state. When the amount of water in the body is increased, the amount of fat is relatively reduced, and the ability to endure low temperatures is poor. On the other hand, when the amount of fat is increased, the ability to tolerate low temperatures increases when the water is reduced. Different developmental stages also have different responses to temperature. Generally, individuals bear the strongest tolerance to low temperature during wintering period, followed by cessation of development or mature larvae, and the developing worms are the weakest.
(5) Insect pests generally have lower endurance to high temperatures than tolerant to low temperatures, and the limits tolerable to them are higher in pests in warmer regions than in colder regions.
Fourth, the impact of humidity on pests The impact of humidity on pests and temperature is equally important, its role in two aspects, on the one hand a direct impact on the physiological activity of pests with water; on the other hand affect the moisture content of pest food, played indirectly effect.
In general, the amount of water contained in the body of a pest is about 50% to 90% of body weight. These waters are solvents necessary for physiological activities such as digestion, circulation of nutrients, discharge of excretions, and adjustment of osmotic pressure, and are also indispensable for body temperature regulation. However, the moisture content of pests often varies depending on the type of pest, the stage of the insect, and the environment. When environmental conditions change, it must adjust this balance with gain and loss of moisture to maintain normal physiological activity.
The moisture in pests is mainly obtained from food. In general, warehouse pests are difficult to survive when the water content of the food is less than 8%, but there are also some pests that are particularly resistant to dryness. For example, the quagmire can live in food with a moisture content of 2%.
Various pests do not have the same requirements for humidity and moisture, but also have the same range of requirements as the temperature. Relative humidity between 70% and 90% is the optimum humidity for most pests. In the humidity range where pests can survive, the role of humidity mainly affects the growth and development rate and reproductive ability.
Insects generally respond very sensitively to changes in the humidity of the environment, especially in response to low humidity. For example, when the rice elephant at 16 ~ 27 °C food moisture content of at least 10% above can survive, if the food moisture content decreased to 8.5%, can only survive 52 days that is self-death. However, some pests can live in dry objects. They often have the ability to resist drying, and some species (such as Mediterranean sea bass) can live in foods that have little moisture. However, in general, if the moisture content of an item drops to 8%, it is not easy to infest.
In addition, oxygen in the air also has a certain impact on pests. When the concentration of oxygen in the air is reduced to a certain degree, it will inevitably affect the respiration of parasites, affect the normal metabolism of pests, and reproduce.