An Overview of Climatic and Genetic Influences on the Emergence of Antheraea spp.

Antheraea mylitta Drury is integral to vanya sericulture contributing about 14.73% of total vanya raw silk production (2021–2022) in India reared across ten tropical and subtropical Indian states. Understanding the impact of genetic and nongenetic factors on the emergence of A. mylitta has been imperative as the bottleneck in successful rearing is observed to be nonseasonal erratic emergence of A. mylitta during the preservation period (diapausing phase of the cocoons). The seasonal months are June to November for the trivoltine and July to October for the bivoltine generations. Nonseasonal unsynchronized emergence leads to failure of successful mating as the male-female ratio becomes close to 1 or often the proportion of females is more leading to crisis of male moths. Evaluation has led to possibilities that the factors regulating emergence were both nongenetic (abiotic) and genetic factors. The abiotic factors predominantly consist of temperature, humidity, and rainfall. The extent to which each factor contributes has been summarized by various workers. Nonseasonal months were further subdivided into zones of minimal emergence (December to February) and zones of unsynchronized or erratic emergence (March to May). During the seasonal months, continuous emergence with 60–70% of males and 30–40% of females occurs resulting in successful mating. However, nonseasonal months witness sudden emergence interrupted by prolonged periods of no-emergence. Of the climatological factors, humidity and precipitation were more deterministic in regulating the emergence. During nonseasonal months, relative humidity is more crucial to emergence; contrary to it, rainfall contributes equally with humidity to bring about emergence in the seasonal months. A stenothermic ambience ranging from 21 to 35 °C throughout the year across the tropical and subtropical India contributes synergistically with either relative humidity or rainfall to cause emergence in A. mylitta population. Temperature alone has non-significant effect to shift the paradigm of A. mylitta emergence. The abiotic factors influence the internal genetic factors in regulating breaking of diapause and subsequent eclosion of adult Antheraea spp. Although species specific information on the genetics of A. mylitta emergence remains unavailable, duality of timeless and period genes in maintaining the biological rhythmicity of Antheraea spp. has been key to emergence. Association of PER protein to Antheraea pernyi circadian clock specific neurons has been deciphered. Diapause and voltinism are the key parameters characterizing the biological or circadian clock of Antheraea spp. The stimulations for break of diapause and emergence of adult moths have been directly linked to PER proteins. PER-positive neurons were connected to eclosion hormones and prothoracicotropic hormones. Expressions of these hormones are seasonal which is extrapolated in Antheraea pernyi. The entire pathway is in a feedback loop. Seasonal phenomenon like change in photoperiodicity directly controls the internal circadian rhythm of the moth. The plausibility of erratic emergence is inversely related to synchronized release of PER and timeless proteins which depends on the synchronization in expression of concerned genes. The expression of genes in turn depends on external climatic conditions which initiates ethological modulations in silkworm from diapause to pre-eclosion to eclosion specific behavior of tasar silkworm.