Host Selection,Food Utilization And Developmental Performances In Dastarcus Helophoroides(Coleoptera:Colydiidae)

Dastarcus helophoroides Fairmaire is a specialist parasitoid of wood-boring long horned beetles.At present,most of studies of it focus on biological characteristics and control effect through releasing adults and eggs,but less attention has been given toward parasitism behavior and food utilization in larvae.D.helophoroides mainly rely on larvae to seek and paralyze hosts,so the parasitism of larvae has a decisive effect on relevant developmental performances and food utilization.To investigate parasitism strategy,developmental performance and food utilization of D.helophoroides larvae,following questions were addressed in this thesis study.(1)Do D.helopho,roides first-instar larvae exist preference to parasitize hosts differed in body size or in parasitization by conspecifics?(2)Are the fitness-correlates of D.helophoroides larvae affected by host mass and host species?(3)Is the food utilization of D.helopho,roides larvae affected by temperature?These studies would provide basic data to understand D.helophoroides larvae in parasitism biology and give us a better understanding in using D.helophoroides in biocontrol practices of long-horned beetles in the field.The main results and conclusions are summarized below.1.Parasitism preference for and developmental performances in hosts of different body sizesThe preference-performance hypothesis has been applied to herbivorous and carnivorous insects that make oviposition selections at adult stage.But few studies focus on the applicability of this hypothesis to ectoparasitoids that search and select hosts at the first larval stadium.We,using ectoparasitoid Dastarcus helophoroides and its long-horned beetle host(Saperda populnea)as the model system,investigated whether D.helophoroides first-instar larvae prefer to parasitize hosts differed in body size or in parasitization by conspecifics.In addition,we,using the regression-based design,observed D.helophoroides developmental life history traits in relation to host body weight at parasitism.The results showed that D.helophoroides first instar larva preferred to parasitize larger S.populnea larvae in body weight;it also preferred hosts parasitized by conspecifics over those unparasitized.D.helophoroides larval development time(averaged to 11.49 d),pupal duration(26.67 d),and larva-to-adult rate(>50%)were not affected by host weight at parasitism.But D.helophoroides adult body weight at emergence significantly increased in relation to host body weight at parasitism,increasing by almost 8%with an increase of each 1 mg host body weight.Our study suggested that D.helophoroides first instar larva may take a trade-off between host body size and parasitization in making parasitizing decisions.In addition,our results lend support for the preference-performance hypothesis.2.Food consumption and developmental performances in different host speciesTo provide data for host selection in mass production of ectoparasitoid Dastarcus helophoroides,we made experiments on D.helophoroides larvae to examine parasitism,food consumption and developmental performances on two host species—S.populnea larvae and the flour beetle Tenebrio molitor pupae.The results showed that the 1st instar larvae had higher parasitization rate on S.populnea larvae(84.3%)than on T.molitor pupae(18.8%).D.helophoroides larvae consumed more and performed better on S.populnea larvae than on T.molitor pupae.D.helophoroides larvae consumed S.populnea larvae by 165.0 mg,significantly more than T.molitor pupae by 111.4 mg,to accomplish larval development.It took 11.5 days on S.populnea larvae to achieve larval development,significantly longer than on T.molitor pupae(9 d).D.helophoroides had higher survival to adults rate(63.3%)on S.populnea larvae than on T.molitor pupae(8.9%).Adult body weight of offspring beetles was greater from attacking S.populnea larvae(29.7 mg)than attacking T.molitor pupae(24.7 mg).These results suggest that S.populnea larvae can support D.helophoroides 1st instar larvae to complete all development,and it can be used as a high quality host in the mass-production of D.helophoroides in biological control program.3.Effects of temperature on food utilizationTemperature has a strong effect on the development,reproduction and population survive of insect.While in larvae stage,optimizing food utilization is essential for achieving maximum adult body size,which is a relevant proxy of fitness.This study aims to understand effects of temperature on nutritional ecology and fitness of D.helophoroides larvae,and then provide basic data for rearing D.helophoroides in the room.We,using six-days D.helophoroides larvae as experiment subject and imposing three temperatures,respectively,20?,25?,and 30?,examined the food consumption and conversion indices.The results showed that the mean body weight gain(after feeding for 1.5 days)and food digested were significantly different between temperature treatments,after adjusting for effects of initial body size.The relative consumption rate and relative growth rate were significantly affected by temperature.The relative consumption rate increased with the temperatures,the relative growth rate increased under 25? than 30?,and under 30? than 20?.The approximate digestibility(AD),efficiency of conversion of digested food(ECD)and efficiency of conversion of ingested food(ECI)were not affected by the temperature treatments.The AD was about 96%under all temperatures,the ECD varied from 73%(20?)to 80%(25?),and the ECI from 71%(20?)to 77%(25?).At 30?,the ECD was 78%and the ECI 74%.These results suggest that the temperature increasing in the proper range was favorable to the food consumption and food utilization of D.helophoroides larva.