Effects of short-term heat treatment on adult's reproduction and longevity of oriental fruit moth, Grapholita molesta Busck

Abstract: 【Objective】The oriental fruit moth, Grapholita molesta Busck, a major pest in orchards of China, is widely distributed nationwide except Tibet. The larva of G. molesta can bore into twigs or fruits, with the feature of generation overlapping and reproducing about 2-7 generations per year. All the features result in the difficulty in forecasting and controlling. In recent years, with the increasing of fruit production, the damage caused by G. molesta has been aggravated in many areas of our country, and has caused devastating impacts on the commercial fruit production. In this study, the influence of short-term heat treatment on the longevity and reproduction of G. molesta was studied to provide a theoretical basis for the accurate prediction of the population dynamics.【Methods】Newly emerged moths were treated at five temperatures for 48 h in climate chambers: (26±1) ℃ (as the control) , (29±1) ℃, (32±1) ℃, (35±1) ℃ and (38±1) ℃, with the relative humidity of (70±10) %, the light period of 15 L:9 D and the light intensity of 4 800 lx to observe the effect of short-term heat stress on the survival rates. Females stressed for 48 h under high temperature conditions were randomly selected and paired with 10 males in control. Then the paired moths continued to be raised at the temperature of (26±1) ℃, the humidity of (70±10) %, the light period of 15 L: 9 D and the light intensity of 4 800 lx. The oviposition and survival rate of each pair was observed and recorded every day until death. In the same way, males stressed for48 h under different high temperature conditions were randomly selected and paired with unstressed females. The paired moths continued to be raised at the temperature of (26 ± 1) ℃, the humidity of (70 ±10) %, the light period of 15 L: 9 D and the light intensity of 4 800 lx. The oviposition and survival rate of each individual was also observed and recorded every day until death.【Results】There was a high mortality for adults at the treatment of 38 ℃ for 48 h. Under this condition, the mortality of females and males was 91.67% and 95%, respectively. There was a significant influence on the pre-oviposition period of females when the corresponding male suffered a short-term heat treatment, and there was a significant impact on the pre-oviposition period of females themselves that were stressed at different temperatures for 48 h. With the increasing of temperature, the oviposition period was shorter. The longest oviposition period was 12 d at 26 ℃, and the shortest oviposition period was 6.67 d for males at 35 ℃. Shortterm heat treatment had significant influence on the egg amount laid by the female. With the rising of the temperature, the egg amount laid by the single female decreased before the age of 10 d. The egg amount laid by the single female was 74.83/♀ in average under the condition of 26 ℃, which was significantly higher than other treatments. The lowest single female egg laying amount was 2.58/♀ when males suffered a short-term heat treatment at 35 ℃. At the same level of the temperature treatment, the influence of temperature on the female was significantly higher than that on the male. Short-term heat treatment had significant influence on the hatch rate of the egg. The hatch rate decreased with the rise of temperature. Under the condition of 26 ℃, the hatch rate was 98.89%, reaching the highest value. The hatch rate was 28.89% when males suffered a short-term heat treatment at 35 ℃. Except 35 ℃, the hatch rate showed no significant difference in whether males or females were treated respectvely under the same temperature stress. Oviposition peak appeared from 5 d to 14 d after eclosion. The earliest oviposition peak appeared at 7 d after eclosion at 26 ℃. With the rise of short-term temperature, the oviposition peak was delayed, and the peak of egg laying amount per day and the longevity of adults decreased. Adults had the longest longevity at 26 ℃, which reached 14.64 d for females and 14.35 d for males. Adults had the shortest longevity at 35 ℃, which reached 10.14 d for females and 9.87 d for males.【Conclusion】Short-term high temperature treatments had significant effects on the survival rate, reproduction and longevity of adults of G. molesta. Among them, the male and female hardly survived at 38 ℃ for 48 h. At 35 ℃, the survival rate was not affected, but the fecundity declined drastically.With the increase of treatment temperature, the life span was shortened, the reproductive capacity was reduced, and the amount of eggs decreased. This indicated that short-term high temperature can significantly inhibit the reproduction and lifespan of G. molesta, which provided a new way for the prevention and control of this pest. Especially in the greenhouses used for growing fruit crops, it is theoretically feasible to control G. molesta by short-term increase of the temperature in the shed.