Effect Of Temperature,Soil And Host Factors On Development And Parasitic Capacity Of Spalangia Endius(Walker) On Bactrocera Cucurbitae(Coquillett)

The melon fruit fly Bactrocera cucurbitae(Coquillett)is one of the dominant fruit flies in South China.The melon fruit fly has seriously threatened the agricultural production and development relying on its high fecundity,rapid spreading and severe damage.Biological control is an effective measure to reduce economic losses of pests.Spalangia endius(Walker)is a single parasitoid of pupae of the melon fruit fly.This study focused on S.endius and explored the effects of temperature,soil and host species on the development,longevity and parasitic efficacy of S.endius.The main results and conclusions are as follows:1.Influences of temperature on the development,longevity and parasitic efficacy of S.endiusThe development of S.endius in pupae of the melon fruit fly was observed at 10?,14?,18?,22?,26?,30?,34? and 38?,respectively.The results showed that S.endius was unable to complete the development in every developmental stage at 10? and 38?,and could complete the development only in the egg and larval stage at 14 ?.S.endius could complete the development in all the developmental stages between 14? and 34 ?.The developmental duration became shorter and the developmental rate became faster with temperature increasing.The body weight and longevity of S.endius differed significantly between 18?,22 ? and other temperatures,but differed insignificantly between 18? and 22 ?.The weights of female and male wasps were significantly higher at 26 ? than those at other temperatures.The developmental threshold temperatures and effective accumulative temperatures of the eggs,larvae and pupae of S.endius were analyzed and calculated.The developmental threshold temperatures of the eggs,larvae and pupae of the parasitoid were 15.02?C,11.13?and 14.07?,respectively.The effective accumulative temperatures of the eggs,larvae and pupae were 19.71,153.61 and 104.59 day-degrees,respectively.The developmental threshold temperature and the effective accumulative temperature for the whole developmental period from egg to adult of S.endius were 11.66? and 301.46 day-degrees,respectively.It was estimated that S.endius could have 10 to 11 generations one year in Hainan Island.The temperature had significant influences on the parasitism ratios and emergence numbers of S.endius.When the temperature was lower than 14? or higher than 38?,S.endius was no parasitic behavior on the pupae of the melon fruit fly and didn't lay eggs.The parasitism ratio and emergence number of S.endius reached the maximum at 26?.The functional responses of S.endius to the pupae of B.cucurbitae conformed to the Holling-?&Holling-? formulas at the range of tested temperatures.The parasitic ability a/Th was 79.08,reaching maximum at 26?.At the same temperature,the parasitic capacity of S.endius increased and the searching effect decreased with the density of B.cucurbitae.The interference effects were strengthened with the density of S.endius.2.Influences of soil factors on parasitic capacity of S.endius to B.cucurbitaeThe pupation and emergence of B.cucurbitae,the parasitic depth,parasitic ratio,emergence ratio and the time of emergence from soils of S.endius were studied in 3 different types of soils and in different soil depths.Soils with different depths significantly influenced the pupation depth,normal emergence rate and mortality ratio of B.cucurbitae.The mature larvae of B.cucurbitae preferred to drill into soils with depth?1 cm to pupate.Pupating depth reached the biggest in the tested sand,which was 11 cm.The biggest depths of pupation in the clay and loam were both 9 cm.The emergence ratio of B.cucurbitae decreased with the pupation depth and the death ratio increased with the pupation depth.The emergence ratios and the death ratios differed insignificantly in the 3 types of soils when the pupation depth was 0-4 cm.When the pupation depth was more than 6 cm,the emergence ratios in the sand were significantly higher than those in the clay and loam,and the death ratios were significantly lower than those in the clay and loam.Soils with different types and different depths significantly influenced the parasitic ratio,emergence number and emergence ratio of S.endius.The parasitic ratio,emergence number and emergence ratio of S.endius reached the maximum when the pupation depth of B.cucurbitae was about 0 cm,which was 94.44%,24.67 and 100%,respectively.The parasitic ratio,emergence number and emergence ratio of S.endius decreased with the pupation depth.When the pupation depth of B.cucurbitae was 1 cm,the parasitic ratios of S.endius were 52.22%,60.0%and 45.56%,respectively,the emergence numbers were 12.33,13.00 and 10.67,respectively and the emergence ratios were 73.08%,95%and 94.19%,respectively.When the pupation depth of B.cucurbitae was 3.5 cm,the parasitic ratios of S.endius were 12.22%,15.56%and 12.22%,respectively,the emergence numbers were 3.67,4.67 and 3.67,respectively and the emergence ratios were 47.22%,58.33%and 72.22%,respectively.The parasitic ratios were relatively higher in the loam and differed significantly when the pupation depth of B.cucurbitae was 1-2 cm.The emergence number and emergence ratio of S.endius differed insignificantly between 3 types of soils.3.Impact of 3 host species on the development and parasitic efficiency of S.endiusThe preference and suitability of S.endius to different hosts were studied using choice and no-choice tests.The results showed that S.endius could all lay eggs and develop to adult in the pupae of B.cucurbitae,Bactrocera dorsalis and Bactrocera tau.However,the parasitoid preferred to parasitize in the pupae of B.cucurbitae.The parasitic ratio in the pupae of B.cucurbitae was significantly higher than that in the other two hosts,and the development duration in the pupae of B.cucurbitae was shorter than that in the other two hosts.