Effect Of Host Plants And Adults Sex Ratios On The Population Of Megalurothrips Usitatus

The bean flower thrips, Megalurothrips usitatus (Bagnall)(Thysanoptera:Thripidae, Megalurothrips), is the most common species in the oriental region. In recent years, the thrips have broken out many times in Hainan Island. In order to control the population of the pest, the frequent uses of the pesticides not only increase the resistence of the pesticides to the pest, but also cause the excess of the pesticide residue on the vegetables in winter. This article studied the effect of the adult's sex ratio to bean flower thrips and the host preference of different crops, and established the life tables of the experimental population on three different leguminous crops. The main results are as below:1. Preliminary studies on oviposition preference of bean flower thrips, Megalurothrips usitatus (Bagnall).Oviposition preferences for three legume species by bean flower thrips, Megalurothrips usitatus (Bagnall), were conducted with leaf discs in the laboratory. In dual-choice tests, the females showed no preference for laying their eggs on either adaxial surfaces or abaxial surfaces of young leaves of both cowpea, Vigna unguiculata, and groundnut, Arachis hypogaea, whereas adaxial surfaces of young leaves of common bean, Phaseolus vulgaris, were preferred for oviposition due to the higher density of trichomes on the abaxial surfaces. When abaxial surfaces of young cowpea leaves and adaxial surfaces of young leaves of both groundnut and common bean were exposed to the females, they expressed clear oviposition preferences for particular legume species in the order cowpea leaves>common bean leaves=groundnut leaves, ovipositing approximately85%of their eggs on young cowpea leaves.2. Life tables for experimental populations of Megalurothrips usitatus (Bagnall) on three leguminous crops.The life table parameters of bean flower thrips, Megalurothrips usitatus (Bagnall), on cowpea, common bean, and groundnut were evaluated at26±1?and60±5%Rh under a photoperiod of14:10-h light:dark. Net reproductive rate (Ro), finite rate of increase (?) and trend index of population (I) of the bean flower thrips had the highest values on cowpea as12.68,1.1413and13.42, respectively. The lowest values of these parameters were recorded on common bean as3.10,1.0692and5.47, respectively. The bean flower thrips had the longest mean generation time (T) on cowpea (19.22days), followed by groundnut (18.76days) and common bean (17.20days). The intrinsic rates of increase (rm) of the bean flower thrips on cowpea, common bean, and groundnut were0.1322,0.0670, and0.1115, respectively. The fecundity per one of the bean flower thrips on cowpea, common bean, and groundnut were28.05,19.85,15.77, respectively. Population doubling time (Dt) on common bean (10.01days) was significantly higher, indicating bean flower thrips population could double62-91%slower in comparison to the populations on cowpea and groundnut. The highest values of survival rate of generation on groundnut as75.49%, followed by cowpea and common bean as68.70and57.03, respectly. It was concluded that cowpea was the most suitable host plant for bean flower thrips, whereas common bean was the least suitable.3. The effect of the adult sex ratio on the reproduction of Megalurothrips usitatusThe experimental results indicated that the bean flower thrips can reproduce its filial generation by using parthenogenesis and bisexual reproduction patterns. The fecundity and longevity per one of the bean flower thrips bisexual reproduction are55%and56%of the parthenogenesis. The sex ratios of the progeny among different mating patterns were between0.32and0.41. The females mating rate was71.67%in a single day with male. That is to say, there were8.60females mated with one male in a single day. And the longevity of the females was influenced by the mating parttens of the males. The results from different mating time of bean flower thrips showed that the female adults after parthenogenesis still could mate with male adults for bisexual reproduction. If the newly emerged female mated with male, the least progeny size and the longevity will be, and there are29.55and7.28d, respectively.