Identification, Physiological Time and Reproductive Potential of Bradysia impatiens (Diptera: Sciaridae) from Liuba, Shaanxi, with a Review Pertaining to Its Occurrences in China

The sciarid fly Bradysia impatiens (Johannsen) is one of the key pests on American ginseng Panax quinquefolium L. in Liuba County, Shaanxi Province, China. Its living specimens were sampled, isolated, reared, mounted, observed and microphotographed. Its identification was completed through both comparisons of morphotaxonomic characteristics and DNA barcoding, and its occurrences in China were reviewed. After conducting serial rearing experiments of the insect at eight temperatures, we calculated developmental threshold temperatures (C) and thermal constants (K) of the species in its egg, larval, pupal and generational stages, and then constructed four reciprocal models N = K/(T − C), where N denotes developmental duration and T is rearing temperature. With values of K and C as well as their SE written, the reciprocal model for its generational stage is Ngeneration = (374.9 ± 8.15)/[T − (6.6 ± 0.29)]. Based on C and K and annual effective accumulated temperatures, we estimated that the sciarid pest would reproduce at a rate of 4.2 to 5.7 generations a year in local regions. In the laboratory, the fecundity of the species was tested to be 59.2 eggs per female, the survival rate of the immature individuals averaged 46.4% in the range from 10.0 to 30.0 °C, and the sex ratio of female to male was 2:1. Based on these coefficients, we are able to estimate the reproductive potential that a parent female and her offspring may reach in a year if they live under favorable conditions, and corresponding economic losses.