Changes Of Biological Characteristics And Protective Enzyme Activities Of Neoseiulus Barkeri Under Short-term Heat Stress

Neoseiulus barkeri(Acari: Phytoseiidae)has the advantages of strong adaptability,short developmental duration and strong diffusion capacity.It is mainly used to control most of the leaf mites,thrips and other small juice sucking pests(mites).Tetranychus urticae,which is rampant in facility agriculture,is one of the problems of strawberry industry in Gansu Province.In this study,N.barkeri was used as the experimental object to explore the effects of different treatment time under different short-term heat stress conditions on the growth,development and reproduction of N.barkeri.In addition,the effect of short-term heat stress on the predation functional response of N.barkeri(Tetranychus urticae as prey)was measured.Finally,the activity of three protective enzymes of N.barkeri before and after heat treatment was measured to reveal the physiological and biochemical mechanism of N.barkeri to shortterm high temperature so as to provide theoretical basis for comprehensive prevention and control of pest mites by using predatory mites in the specific high temperature environment of facility agriculture.The results are as follows:1.Effects of short-term heat stress on the growth,development and reproduction of Neoseiulus barkeriThe hatching rate of eggs and the development duration of different immature stages of N.barkeri were studied in the laboratory at four temperatures(38℃,40℃,42℃ and 25℃ as control)for 2,4 and 6h.The adult females were treated at the same condition after emerged.The results showed that the egg hatching rate decreased with the increase of the temperature and the prolongation of the treatment time.The eggs treated at 42℃ for 2h or more could not hatch or shriveled.The developmental duration of each immature stage decreased first and then increased.The oviposition period and longevity of adult females at 38℃ were shortened with the prolongation of treatment time,and the fecundity showed a trend of first decreasing and then increasing.At 40℃,the fecundity oviposition period and longevity of adult females increased slightly with extension of treatment time.The hatching rate and developmental duration of immature stages were significantly affected by short-term heat stress,and the oviposition period,fecundity and longevity of adult females were also affected.2.Effects of short-term heat stress on the activities of three antioxidant enzymes of Neoseiulus barkeriFour temperatures(38℃,40℃,42℃ and 25℃ as control)were set in the laboratory.The adult females of Neoseiulus barkeri were treated at the temperatures for 2h,4h and 6h,and the changes of the activities of three protective enzymes were measured.The total protein content of N.barkeri gradually increased with the increase of temperature and time,and the overall antioxidant capacity also increased gradually.At 38℃,with the extension of treatment time,CAT activity showed a trend of increase-reduce-decrease;POD showed a trend of increase-reduce-increase;SOD showed a trend of increase-reduce-increase.However,at 40℃,the variation trend of the three was the same: increase-reduce-increase.Heat stress upregulated the activities of three antioxidant enzymes in N.barkeri,interfered with the dynamic balance of reactive oxygen species(ROS),and increased the protein content of N.barkeri.3.Effects of short-term heat stress on functional response of Neoseiulus barkeriIn this study,three stages of T.urticae including egg,nymph and adult(female)were used as prey to investigate the functional response of N.barkeri after treated for 2,4 and 6h treatment at 38℃,40℃ and 42℃,with 25℃ as the control.The results showed that shortterm heat stress had certain inhibitory effect on the consumption of adult females.Fitting results indicated adult females of N.barkeri exhibited a type II functional response to every stage of T.urticae in this study whether the predators were exposed to heat stress or not.However,the obvious decreased consumption on preys of N.barkeri was recorded,which mainly manifested in the fluctuations of related parameters such as the attack rate(a),handling time(Th)as well as the value of(a/Th).With the increase and prolongation of heat shock and treatment time,the overall predation ability of N.barbari decreased gradually.The consumption preference on different states of T.urticae under the same temperature was egg>nymph > adult,short-term high temperature had no effect on the type of functional response,but the predation ability was obviously restricted.