Effects Of Migration On Reproduction And Its Physiological Mechanisms In The Beet Webworm, Loxostege Sticticalis(Lepidoptera: Pyralidae)

The beet webworm, Loxostege sticticalis(Lepidoptera: Pyralidae) is a worldwide insect pest of pasture and crops in the Northern, Northwestern and Northern China. Severely economic losses have caused by it since 1949. Migration is one of the major life strategies for the beet webworm on adaption and reproduction under atrocious conditions and it is also the major reason of frequent outbreaks of L. sticticalis. Many studies about the regulation and the effect of migration have been researched but the physiological mechanisms of these are not well known. Using the principle and methodology of eco-physiology, effects of migration on reproductive behavior and energy, and the interrelation of reproduction system and flight system were studied. The main results are as follows:1. Effects of migration on reproductive behavior and population outbreak of the beet webworm, L.sticticalis were investigated. The results showed that preoviposition period, oviposition period, PFO and adult longevity of migrant population were significantly reduced as compared those of unmigrant population. However, mating frequency and mating percentage were significantly increased, while adult life time fecundity and egg hatch ratedid not vary significantly. The results indicated that although adult egg production did not significantly increased, the migrant population could mate for several times quickly and oviposited eggs in advance obviously, and the egg-laying synchrony increased significantly as well, which serve to increase the subsequent larval density and population outbreak.2. The investigations of dynamics of flight muscle and ovary after flight show that the ovariole diameter was significantly shortened and the ratio of high level of ovary was significant lower than that of control. With the extension of time, the ovariole diameter developed significantly and was no difference at the first day. The ratio of high level of ovary was significantly higher than that of control at the third day after flight. The soluble protein was declined dramatically, but was higher than the control all the time. Myofibrils diameter, the length of sarcomere and the ratios of the two were significantly higher than that of control. Myofibrils diameter, the length of sarcomere and the volume fractions of myofibrils increased at the first day but then decreased, especially on the second day after flight, while the soluble protein, myofibrils diameter, and the length of sarcomere decreased significantly. The results indicated that the development of ovary was restricted when flying, but it could recover after flight and lead to produce mature eggs at a time in individuals, while the development of muscle was promoted because of flight, the degradation of flight muscle was speed up.3. Glycogen of thorax and abdomen were significantly lower than the control, and triglyceride of abdomen was shorter significantly but not the thorax. The ratio of ADP and ATP were higher than that of control. Glycogen, triglyceride and ADP/ATP were always increasing after flight. Glycogen had no significant difference with the control at the first day after flight, whereas the glycogen of thorax was higher significantly than that of control at the third day after flight. Triglyceride had no significant difference with the control at the second day and droped significantly after the time. ADP /ATP of thorax was decreasing all the time, and the ratio of abdomen was declined at the first day and then had great significant lower than the control. The results indicated that the accumulation amount of glycogen raised and the speed of triglyceride increased.4. The studies of dynamics of food intake after flight revealed that the content of 2-NBDG of flown moths was significantly higher than that of control in the 12 h after flight, but the content of 2-NBDG had no significant difference with the control from 12 h to 24 h after flight. The results indicated that flight could accelerate the food oaccumulation after flight. The above results illustrate that the synchrony of first egg-laying increased and the advanced degradation of flight muscle, the fast development of ovary and the increased food intake were good for this. These results will be helpful for the study of effects and physiological mechanism of outbreaks, and provide evidences for forecast and recognition of effects on reproduction.