Differences In Impact Of Asecodes Hispinarum Parasitism On Larval Developmental Process And Cellular Immunity Of Two Bettles

Brontispa longissima Gestro and Octodonta nipae Maulik are major invasive pests that attack palm plants in China.The endoparasitoid Asecodes hispinarum Bou?ek is a classical biological control agent of B.longissima larvae.The parasitoids also parasitize O.nipae larvae,however,their offsprings can not fulfill the development.To understand the possible mechanisms behind this,in the present study,the fitness variations of A.hispinarum in its two different kinds of hosts,B.longissima and O.nipae,were investigated,including the parasitic and oviposition selection,and the development.Further,the differences in cellular immune response of the two hosts to A.hispinarum were analyzed.The main results are as follows.1.When targeting the single host or the two hosts simultaneously within 48 hours,A.hispinarum showed no preference for the parasitic selection,but showed variations in the number of offsprings on the two hosts.In non-choice and dural-choice experiments,the number of wasp eggs layedin B.longissima larvae were 19 and 18,respectively,while in O.nipae larvae the offsprings were 16 and 15,respectively.2.The offsprings of A.hispinarum could normally grow and develop in the larvae of B.longissima,and the larvae become mummified within 7 days,which caused the high mortality of 98.95%.In contrast,the offsprings of the parasitoid in O.nipae larvae could not develop normally,but the parasitism led to a mortality of 15.62% in the larvae,and extended the duration of larval and pupal period with increasing by 5 and 1 d,respectively.The results suggest that parasitism of A.hispinarum showed adverse impacts on the development of O.nipae.3.In vivo,the encapsulated eggs of A.hispinarum were only 1.14% in the host B.longissima larvae,while were up to 99.05% in O.nipae larvae.Similarily,in vitro,the encapsulated eggs were 14.29% by B.longissimi larvae hemocytes,but were increased to 39.50% by the hemocytes of O.nipae larvae.4.Total hemocyte counts(THCs)in the fourth instar larvae of B.longissima and O.nipae were maintained at relatively stable levels during their development.The THCs in the latter were 6.08 times higher than that of the former.The THCs in B.longissima larvae were 1.83 times higher than that at 24 h after parasitization by A.hispinarum when compared to that in non-parasitization larvae.While the THCs in O.nipae larvae were respectively 1.65,1.63 and 1.56 times higher than that at 48,72,and 96 h following parasitization compared with non-parasitization larvae.It can be seen that the sufficient number of hemocytes is the basis for the successful encapsulation of A.hispinarum eggs in O.nipae larva.5.The proportion of plasmatocytes did not vary and the granulocytes were 1.20 times higher than that in B.longissima larvae parasitized by A.hispinarum at 24 h compared to that in non-parasitization larvae.While in O.nipae larvae parasitized by the wasp,the proportion of plasmatocytes were 1.09 times lower than that at 12 h and were respectively 1.65,1.63 and 1.56 times higher than that at 24,72 and 96 h,and the proportion of granulocytes were 1.07 times higher than that at 12 h,compared to that in non-parasitization larvae.The results showed that parasitism by A.hispinarum affected the different hemocyte counts(DHCs)more obviously in O.nipae larvae than in B.longissima larvae.In conclusion,A.hispinarum offsprings were unable to successfully develop in O.nipae larvae,but the parasitism caused an adverse effect on the development of host O.nipae larvae.The sufficient number of blood cells and the more obvious response of hemocytes,including THCs and DHCs,to A.hispinarum eggs in O.niape larvae may be the possible reasons for the successful encapsulation of the wasp eggs.