| Xestia c-nigrum is a key polyphagous underground pest that usually cause serious economic loss to a variety of crops such as cotton and corn.The sterile insect technique(SIT)is an environmentally friendly and less resistant pest control method,which has been applied to control pests in agro-forestry ecosystems.In this study,we first assessed how different temperatures affect the development and reproduction of this pest by using insect lifetable method in the agricultural production area of Xinjiang province,China.Then,we specially evaluated the effect of X-ray irradiation on their fertility,longevity of X.c-nigrum and the egg hatching,larval development of the offspring(F1 generation).The study will be benefit in selecting the suitable dose to lead to male sterile of X.c-nigrum and proposed the sterile irradiation technique for X.cnigrum.The main results of this study are as follows:1.The effect of temperature on the life parameters of the X.c-nigrumThe survival rate of different development stage of X.c-nigrum was varied among different temperatures,the survival rate of the larvae was < 20% at 15℃,whereas < 2% at 30℃and 35℃,but were higher at 20℃ and 25℃.The duration of different development stages of X.c-nigrum shorted as the temperature rose,and the egg duration from 15°C to 35°C were 15.5 d,7.4 d,5.5 d,4.9 d,and 3.9 d,respectively.The larvae duration from 15°C to 30°C were 109.4 d,40.5 d,26.5 d and 24.5 d,respectively.The pupal duration from 15°C to 25°C were 41.4 d,18.0 d and 12.5 d,respectively.The larval survival rate was highest at 20°C,which was 50.74%.At 25°C,the pupation rate,relative eclosion rate,average fecundity,intrinsic rate,finite rate and net reproductive rate were all the greatest.When the temperature is higher than 30 °C,the X.c-nigrum cannot complete the individual development normally.The developmental threshold temperatures of egg,1 to 6 instar larvae and pupae of X.c-nigrum were 9.81℃,8.43℃,9.95℃,10.26℃,12.52℃,13.58℃,12.60℃ and 10.81℃,respectively,and the effective accumulated temperatures were 79.62 d·°C,92.17 d·°C,56.09 d·°C,57.03 d·°C,39.35 d·°C,38.16 d·°C,80.72 d·°C and 172.39 d·°C,respectively.X.c-nigrum could have three generations per year in Korla,Xinjiang,and the peak insect trapping periods are in mid-May,late July and early September,with the relative average temperature at the range of 19.5~26.5℃,respectively.2.The effect of X-ray irradiation on the reproductive ability of the X.c-nigrumHigh dose of X-ray irradiation had a significantly negative effect on the reproductive ability of the parental generation,for instance,the eclosion and reproduction of the female adult.Among the 7 dose treatments of 10 Gy,30 Gy,50 Gy,100 Gy,200 Gy,300 Gy and 400 Gy,the eclosion rate of male pupal was lowest with only 5.25% at 400 Gy,which was significantly lower than 95.25% of CK(0 Gy)and other irradiation treatments.The total fecundity under all irradiation treatments were lower than 420.4 eggs of the CK,with the lowest fecundity with 127.0 eggs at 200 Gy.The longevity of male adult significantly decreased as the increase of irradiation dose,which was 15.6 d of CK,and < 10 d when the irradiation dose was higher than 200 Gy.The number of mating times was ranged of 0~4 times,and the CK treatment had the highest number(4 times)of mating times,which was higher than these irradiation treatments.The cumulative numbers of mating and sperm count under each irradiation treatment were lower than those in the CK group,and the mating cloud not be found when the dose of X-ray was higher than 200 Gy.3.The effect of X-ray irradiation on the development of X.c-nigrum offspringIrradiation doses of X-ray can significantly affect the growth and development of the offspring of X.cnigrum.The hatching rate of F1 generation decreased with the increase of irradiation dose,which was significantly lower than 52% of CK when the dose was higher than 50 Gy(with the hatching rate was 21%),and these eggs could not hatch at 200 Gy and 400 Gy doses.The larval survival rate of F1 generation was also decreased with the irradiation doses,with only 22% of larval can survive to pupal at 300 Gy dose.Irradiation significantly delay the development period of F1 generation larval,and the 100 Gy treatment was of 32.3 d,which was significantly higher than 26.7 d of CK.The eclosion rate of F1 generation at 100 Gy was 64.73%,which was significantly lower than that of CK of 99.66%.The fecundity of F1 generation at a dose of 100 Gy was 164.4 eggs,which was significantly lower than 334.2 eggs of CK.After the oviposition of F1 generation adult,the hatching rate of their offspring(F2 generation)was also varied significantly between different treatments.The hatching rate of F2 generation at 30 Gy dose was 47.04%,which was significantly lower than CK(79.61%).However,when the dose was higher than 50 Gy,the hatching rate of F2 generation eggs was close to 0%.This study indicates that the week adaptability of this pest to high temperature,and 20~25°C is more suitable for its growth and reproduction,which is consistent with the temperature variation at the peak period for the field population.X-ray irradiation has obvious effects on the parental reproduction and offspring growth and development of X.c-nigrum,the 400 Gy dose of X-ray irradiation can make the parents utterly sterile of X.c-nigrum,100 Gy dose treatments can control the F1 generation at a low level while having the ability to mate,and comprehensively consider 100 Gy as the screening dose for male sterility in the field.This provide an important foundation for the population release and integrated management tactics to control X.c-nigrum. |
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