Studies On Ecological Adaptability Of The Mirids

Area-wide cultivation of transgenic Bt cotton has effectively controlled the cotton bollworm Helicoverpa armigera with resulting reductions in the amount of broad-spectrum insecticides used in cotton production. This lowered insesticide use has caused the mirids to be major pest insects on Bt cotton in China. Furthermore, these pests have spread to a range of other crops, e.g. Chinese date Zizyphus jujuba, grape Vitis vinifera. The mirids were often treated as a secondary pest with limited studies in China. In order to clarify the mechanisms of geographic distribution and occurrence of each mirid species, and provide a base for developing integrated management measures, we study the ecological adaptabiity of four dominant mirid species, including Apolygus lucorum, Adelphocoris suturalis, Adelphocoris fasciaticollis, Adelphocoris lineolatus. The main results were summarized as follows.Temperature had great impacts on the survival, development and fecundity of four mirids. Development rate increased greatly with increasing temperature ranging from 10 to 30oC, followed by a slight decrease at 35oC. According to the degree-day equation between development rate and temperature (10-30oC), the lower development thresholds and degree-day accumulations of egg A. lucorum, A. suturalis, A. fasciaticollis, A. lineolatus were 3.21oC and 179.27DD, 5.60oC and 189.86DD, 6.26oC and 188.81DD, 5.58oC and 231.66DD, those of nymphs were 3.68oC and 301.96DD, 5.03oC and 308.83DD, 3.04oC and 366.73DD, 6.23oC and 291.64DD, respectively. Based on the Logan VI models describing the relationship between development rate and temperature (10-35oC), the optimum range for eggs and nymphs development were estimated form 32oC to 34oC. Egg incubation rate was high at 20-30oC, nymphal survival rate and adult fecundity were great at 15-30oC. Longevities of the adults greatly declined with increasing temperature without great difference between genders.Each mirid species showed different preferences to various host plants in the field. Among more than 100 plants tested, A. lucorum preferred to mungbean Phaseolus radiatus, Vicia faba, Coriandrum sativum, Chrysanthemum cornarium, Ricinus communis, Impatiens balsamina, Humulus scandens, Artemisia lavandulaefolia, Artemisia annua and other plants. A. suturalis showed great preference to Astragalus complanatus, Medicago sativav, Agastache rugosusv, A. lavandulaefolia, V. faba, Dianthus superbus, Melilotus albus, Schizonepeta tenuifolia and others. A. fasciaticollis greatly liked Lablab purpureus, Artemisia scoparia, I. balsamina, M. sativav, Leonurus heterophyllus and others. The major preferrd plants of A. lineolatus were M. sativav and M. albus. In Y-tube olfactometer assays, volatiles from mungbean plants elicited a strong attraction of both A. lucorum sexes than those from mungbean plants. Headspace extracts from mungbean and cotton were analyzed by coupled gas chromatography–electroantennographic detection (GC–EAD), and a total of four major compounds were found to elicit electro-antennogram (EAG) responses. Two EAD-active volatiles identified from cotton plants were 1, 3-dimethyl-benzene and 2-propenoic acid, butyl ester, while other two volatiles from mungbean plants were acetophenone and nonanal. Among these volatiles, acetophenone elicited the greatest EAG responses than others. All the four mirids had great flight capacity, A. lucorum was the greatest, and A. lineolatus was the weakest. For these four species, 10-d-old adults flied for 25-45 km over 24-h period. Age exerted great effects on it, flight capacities of the adult aging day 5-15 were usually great, and those of the new-emergent and old-aged adults were comparatively low. Female A. lucorum had the greater flight capacity than the males, while flight performance was similar between genders for other three species. Mating status only had minor effects on flight performance of the various species. Temperature and relative humidity greatly affected flight capacity, with 18-23oC and 64-68% RH considered optimal for flight of all the species. Both high and low temperature and relative humidity were unfavorable for their flight.A. lucorum had about 80 species of overwintering host plants, including Z. jujuba and some other fruit trees. A. suturalis had the similar number of overwintering host plants. For A. fasciaticollis, only about 10 species could be considered as its overwintering host plants. A. lineolatus had about 30 plant species suitable for overwintering. Among these species, some pastures, such as M. sativa, may be the major ones for A. lineolatus. All the four mirid species not only could oviposit in live plants, but also can lay eggs in withered ones. In addition, A. lucorum and A. suturalis can lay eggs in the soil and successfically live through the winter.