| Sitobion avenae(Fabricius)is a major pest infecting cereals worldwide;this species is dominant in main wheat production regions of China.During long-distance dispersal,alates most likely undergo a brief starvation period because they lack a suitable host.The present study examined the ovarian development and potential reproduction of alate adult morphs of S.avenae under starvation stress.We evaluated the potential effects of maternal starvation periods on the offspring.On the basis,the feeding behavior of the starved aphids after subsequent feeding was analyzed by EPG technique combine with honeydew secreted,and determined the effects of starvation periods on titres of ecdysone using ELISA.These findings have implications for further research relevant to reproductive adaptation of migratory aphids.(1)The current study examined ovarian development in the alate aphid S.avenae in relation to the presence or absence of food,and estimated the effects of different starvation periods and subsequent feeding on life span and total fecundity.Results indicated that continuously fed and starved aphids contained two telotrophic ovaries,each comprising five ovarioles.With increasing time after emergence,the number of offspring produced by the fed aphids increased gradually,whereas the number of embryos in their ovaries decreased gradually.Both the number of mature embryos and the volume of embryos rapidly increased at 24 h after emergence,and then remained at an approximately constant level between 24 and 144 h.Compared to the fed aphids,starved aphids only produced a small number of nymphs,and there was no significant change in the total number of embryos between 24 and 144 h,whereas both the number of mature embryos and volume of embryos increased significantly.Irrespective of starvation period,highly significant relationships between life span and fecundity were found.Adult aphids starved for longer periods presented lower longevity and fecundity,but dead females contained more mature embryos than those starved for shorter periods.These results suggested that,under starvation stress,S.avenae tends to invest in the development of larger embryos at the expense of reducing lifespan and future fecundity.(2)The current study examined the effects of maternal starvation in the alate aphid S.avenae in relation to the presence or absence of food.Results indicated that the survival rate of the alate adults of S.avenae in the starvation group was lower than that in the feeding group at the same period after emergence.Few offspring was born during periods of starvation but the number of offspring produced within 24 h of resumption of feeding in the starvation group was higher than that in the feeding group at the same period after emergence.With the increase in the degree of maternal starvation,the offspring volume at birth decreased significantly within 24 h of resumption of feeding.Offspring from mothers starved periods of ? 96 h was smaller significantly than that from fed mothers at the same period after emergence.Offspring from starved mothers raised individually under normal food conditions,their development duration increased significantly with the increase in the degree of maternal starvation.Offspring from mothers in the 120 h and 144 h starvation treatments delayed significantly 15.1% and 15.8%,compared with that from fed mothers at the same period after emergence.However,maternal starvation experience,under normal food conditions,had no effects on the apterous ratio,survival rate,adult life span,and total fecundity of offspring within 24 h of resumption of feeding.(3)Starvation affected obviously the feeding behavior resumption of host plant of the alate adults of S.avenae.Before the phloem feeding,the stylet showed to probe the surface and internal tissues of wheat leaves.The total duration of G wave of the starved aphids was higher than that of the fed individuals,indicating that the starved aphids rapidly recover the water balance through the active ingestion in host xylem.With increasing time after starvation emergence,the total duration of E1 wave was increased and significantly higher than the feeding individuals,indicating that the starvation increased the time of phloem ingestion.Feeding behavior of the phloem was related to starvation time.The total duration of E2 wave in the 24~72 h starvation treatments was significantly higher than in the fed aphids at the same time after emergence.Accordingly,there was a higher level of honeydew secretion.However,the total duration of E2 wave in the 96~144 h starvation treatments was significantly lower than that in the fed aphids at the same time after emergence.Accordingly,there was a lower level of honeydew secretion.Highly positive relationships between honeydew secretion and the total duration of E2 were found.(4)With increasing time after emergence,the titres of 20 E increased significantly both the starved aphids and the fed aphids of alate S.avenae adults.Moreover,the titres of 20 E of the starved aphids was significantly higher than that of the fed individuals at the the same time after emergence.Each ovariole includes three or four embryos.With increasing of starvation time,the lager embryos continue to develop,and small embryos still exist.After 24 h starvation,the foregut shrinked and the diameter of the midgut decreased,with a significant decrease in the number of epidermic cells,which indicates the gut permeability increased,,when starved 120 h,the phenomenon is more obvious.Insects can respond to resource-poor conditions by reproductive physiology.Under starvation stress,S.avenae safeguards the development of their current embryos at the expense of reducing longevity and future fecundity.Live aphids after starvation treatment settle down the suitable host plants,meaning that individuals from unfavourable food condition can produce offspring on favourable food condition.Most offspring are produced within a short time of the adult aphids recovering feeding.These results suggest that alate S.avenae adults are able to show flexibility by taking account of food heterogeneity,and adjusting their commitment to spreading their offspring in time and space accordingly.Feeding behavior and a high level of 20 E titre might be adaptive characteristics under starvation stress.This adaptive strategy is important in understanding their successful reproduction in new habitats during dispersal.Our findings have implications for pest management of S.avenae,or further research relevant to reproductive adaptation. |
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