Okay, here is the translation following your instructions: Tobacco Entomology

Author: Wei Chongsheng et al. / Country:
Publisher:
Publishing Date: 2002-08-01
Features: Section 3: Generations and Annual Life Cycle of Insects
The individual development cycle of insects from egg to adult maturity and the beginning of reproduction is called a generation. The development history of an insect within one year, or more accurately, the development process from the hibernating stage of the current year to the end of hibernation the following year, is called an annual life cycle (or simply life cycle). Studying the life cycle of pests is essential for understanding their biological characteristics, making predictions and forecasts, and formulating control strategies. The time required for different insects to complete a generation varies, and the number of generations they can complete in a year also differs. Some insects have only one generation per year. For example, the big earthworm moth is called univoltine, which is determined by the genetic characteristics of the species. Some insects can have two or more generations per year, such as the tobacco cutworm, which can have 2 to 6 generations per year depending on the region, and is called multivoltine. Some insects have life cycles that take 2 or more years, such as the June beetle, wireworm, and North China mole cricket. The number of generations a species has per year varies with the effective accumulated temperature for development or altitude in its distribution area. Generally, it increases with decreasing latitude and decreases with increasing altitude. The duration of a generation and the number of generations that occur in a year vary among insect species but are often closely related to environmental factors, primarily climatic factors. This can be seen from the number of generations that different insects undergo in different distribution areas. For example, the tobacco cutworm has 3 to 4 generations per year in Shaanxi, 5 generations in Fuquan, Guizhou, and 6 to 7 generations in Hunan and Sichuan. Insects develop from eggs as the starting stage of a generation, meaning the time from egg to adult is the same generation but different stages. The calculation of insect generations generally starts from the appearance of eggs in the current year, followed by the first generation, second generation, etc. Overwintering eggs from the previous year that hatch in spring are also considered the first generation of the current year, while overwintering larvae, pupae, or adults from the previous generation are not considered the first generation of the current year but rather the last generation of the previous year, which is specifically called the overwintering generation. Some migratory pests that cannot overwinter locally, such as the armyworm (Spodoptera litura) and the small cutworm, are called the first-generation adults upon their initial migration, or the first-generation pest source. Insects that have multiple generations per year often exhibit staggered generations due to irregular emergence periods, long adult molting and egg-laying periods, resulting in overlapping generations, making it difficult to distinguish between different generations, a phenomenon known as generation overlap. Generally, the more generations that occur in a year, the more severe the generation overlap. Additionally, due to uneven insect development, localized generations may occur in later generations. For example, the tobacco cutworm often overwinters as the fourth-generation larvae in Anhui, but some continue to develop into the next generation, which is called the localized generation. These two situations often pose challenges in pest control.
Section 4: Insect Dormancy and Diapause
Like other arthropods, insects often have periods of growth and development stagnation during the year, such as during severe winter or summer, which is commonly referred to as hibernation or aestivation. Broadly speaking, hibernation or aestivation is merely a superficial phenomenon of safely passing through adverse environmental conditions. However, based on the conditions that induce or eliminate this phenomenon and the insects' responses to these conditions, we can divide this developmental stagnation into two distinct types: dormancy and diapause.
### 1. Dormancy
Dormancy in insects is often directly caused by adverse environmental conditions, such as the drop in temperature during autumn and winter in temperate or cold-temperate regions, or the high temperatures and drought in tropical regions, which can induce dormancy in some insects. Insects with dormancy characteristics may exhibit it during specific stages, such as the migratory locust (Locusta migratoria manilensis), which enters dormancy during the egg stage. Others may enter dormancy during different stages, such as the small cutworm, where adults, larvae, and pupae can all hibernate in the Yangtze-Huai River region southward. However, when adverse conditions are eliminated and the necessary conditions are met, dormancy will terminate, and growth and development will resume. Such insects can reproduce year-round under artificial temperature control in winter or in warm southern winters. Due to the physiological differences among different insect stages and ages, their resistance to adverse conditions varies, resulting in different mortality rates during hibernation, which can affect the population base for the following generation.
### 2. Diapause
Diapause can also be caused by environmental conditions, but it is not directly induced by adverse conditions. In natural conditions, insects enter diapause well before adverse conditions arrive, and once diapause begins, even if favorable conditions are provided, they will not immediately resume growth and development. They require certain stimulatory factors (such as low temperatures) to return to suitable conditions before growth and development can continue. Therefore, it has a certain genetic stability. Diapause can be divided into obligate diapause and facultative diapause. Insects that enter diapause without a fixed generation are called facultative diapausing insects, typically those with multiple generations per year, which can vary with geographical conditions, seasonal climate, or food factors. For example, the cotton bollworm (Heliothis armigera) has 3 generations north of 40°N latitude, 4 generations between 40°N and the Yangtze River, and 5 to 6 generations south of the Yangtze River, but all enter diapause as pupae in the last generation to overwinter. Insects that enter diapause at fixed generations and stages are called obligate diapausing insects, typically those with one generation per year, which enter diapause at fixed times regardless of external conditions. For example, the big earthworm moth has one generation per year in both northern and southern regions and enters diapause as mature larvae.
In addition to genetics, seasonal photoperiod (the rhythm of day and night light and dark hours) is the main factor causing diapause in insects. The photoperiod that induces 50% of the insect population to enter diapause is called the critical photoperiod. Different insect species or different geographic populations of the same species may have different critical photoperiods. Since each insect has a fixed diapausing stage, it indicates that the sensitivity to light stimulation is also fixed to a specific stage. Experiments have shown that this stage (instar) is often the preceding stage (instar) of the diapausing stage, known as the critical photophase (instar) in ecology. For example, the cotton bollworm that diapauses as a pupa has a critical photophase as the fifth instar of the preceding larval stage; the silkworm that diapauses as an egg has a critical photophase as the adult of the previous generation. Most insects that diapause in winter use short daylight as the signal for diapause. Typically, if the photoperiod is longer than 12 to 16 hours, they can continue to develop without diapause, and such insects are classified as short-day diapausing types (long-day development types). Conversely, some insects that enter diapause in summer use long daylight as the signal for diapause. If the photoperiod is shorter than 12 hours, they can continue to develop without entering diapause, and such insects are classified as long-day diapausing types (short-day development types).
In addition to photoperiod, temperature and food are also important environmental factors that induce diapause in insects. Under natural conditions, changes in photoperiod are always correlated with temperature changes. Experiments have shown that appropriate high temperatures can inhibit diapause in short-day diapausing insects. Insect food also affects the progress and proportion of diapause. The main factor that breaks diapause is low temperature (above 0°C). Secondarily, the diapause of some insects requires stimulation from the photoperiod. During dormancy and diapause, insect life maintenance entirely depends on the nutrients stored before dormancy. Physiologically, the rate of respiratory metabolism decreases sharply, oxygen consumption decreases significantly, and fat storage and carbohydrate content increase. The water content in the body, especially free water, decreases significantly. Therefore, when insects enter dormancy or diapause, their resistance to adverse conditions significantly increases, enhancing their tolerance to cold, drought, and pesticides. Insects that hibernate or diapause in winter have specific overwintering stages and locations. For example, the stink bug overwinters in hidden places such as wall crevices and tree bark crevices; the tobacco stem borer overwinters as larvae or pupae inside tobacco plants; and the tobacco aphid overwinters as eggs on peach trees. Understanding the dormancy and diapause characteristics of insects, as well as the overwintering stages and locations of pests, can help predict pest occurrence and damage periods, providing direct guidance for winter control measures.