Selectivity of Frankliniella occidentalis to vegetable hosts

Western flower thrip,Frankliniella occidentalis,is one of the most serious pests in vegetable production worldwide.Its damage to crop production results from direct feeding as well as serving as a vector of plant viruses.F.occidentalis invaded China in 2003,and now has been reported in several provinces of the country.F.occidentalis is a polyphagous species with more than 500 plant species belonging to 62 different families.It is reported that there are significant differences at the selectivity of F.occidentalis on host plants.However,the selectivity of F.occidentalis has not yet been studied in China.In this paper,the host selectivity of F.occidentalis was studied through the field investigations,the indoor free choice tests,as well as the research on the effect of different vegetables on the development and fecundity of the insects. The field investigations showed that F.occidentalis could occur on 24 kinds of vegetables with quite various populations,indicating that F.occidentalis had obvious preference behaviors in host selection.The fitness of host plants to F.occidentalis was quantitatively measured with selective index(I) and preference index(P). The selective index was the biggest,the value of 1,for 9 vegetables,such as kidney bean,radish,cucumber,and eggplant,and the lowest selective index was 0.2 for celery.The preference indexes were different among host plants too,with the biggest value 0.8 for kidney bean,and lowest on water spinach.According to the indexes,the host plants of F.occidentalis may be categorized into 4 groups,(1) the most favorite hosts,such as kidney bean,eggplant,cucumber,radish and coriander;(2) favorite hosts,such as hyacinth bean,soybean,lettuce and sponge gourd;(3) secondary favorite hosts,including cowpea,broad bean,pepper and amaranth;and(4) non-favorite host,such as tomato,garlic and celery.There was an obvious linear relation between P and I,with the regression equation of P = 0.7937I-0.2734. The indoor free choice tests showed that the number of adults and eggs were greatly different on different vegetables under the coexistence of 7 vegetable hosts(cucumber,kidney bean,eggplant,lettuce,cabbage,celery and garlic),the greatest number of adults landing on the surface was found on cucumber,and the most eggs was laid on cucumber and kidney bean.Both of the number of adults landing and eggs laid were the lowest on celery and garlic.The developmental periods and survival rates of F.occidentalis were significantly different among the vegetables.F.occidentalis had the fastest development when feeding on cucumber,with immature stage of 11.43 d,and the slowest growth on celery with the immature stage of 16.1d. The experimental results indicated that there were significant differences of larval survival rates on several hosts ranging from 72.55% to 98.00%. It was found that the lowest survival rate of immature stage was 57.14% on celery.F.occidentalis could lay eggs in all the 7 kinds of vegetables,but there were significant differences in the number of eggs laid in each host.Each female deposited 0.45 eggs per day on garlic,4.43 on kidney bean.In conclusion,the results in field and in door tests showed that F.occidentalis had obvious selectivity to vegetable hosts,and field investigation results in selectivity of F.occidentalis to vegetables were basically in accordance with those of indoor tests.