Effects Of Supplementary Food On Longevity And Fecundity Of Meteorus Pulchricornis (Hymenoptera: Braconidae)

Parasitoids are an important factor in the regulation of insect pest populations. Some studies show that adult females of many parasitoid species obtain materials necessary for maintenance and survival. Lack of a food source could influence many other aspects of parasitoid biology such as searching efficiency, fecundity and longevity. For most parasitoids, the food source was not known, but we could readily assume that adult parasitoids could feed directly or indirectly on plants in the field. Direct plant-derived food include floral and extra floral nectar, pollen and some plant lactates; indirect plant-derived food include honeydew produced by Homopterous such as aphids, mealy bugs, scale insects and whiteflies. However, the availability of sugar sources varied in both natural and agricultural settings. Many studies indicate that distinct differences exist between insects in their ability to utilize sugars in different sources and concentration.Meteorus pulchricornis (Wassail) [= japonicas Ashamed] is a solitary beaconed endoparasitoid attacking the larval stages of numerous Lepidopteron pests, such as the gypsy moth (Lymantria dispar L.), the cotton bollworm (Helicoverpa armigera Huber), beet armyworm (Spodoptera exigua Huber) and (Spodoptera literal Fabric us) . Both biparental and uniparental strains were reported whereas the later strain was used in this study. Until now have most of studies been contributed to understanding the interactions between the parasitoid and hosts. However, little is known about affects of supplementary nutrition on adult longevity and fecundity of M. pulchricornis. This knowledge would help to understand the foraging behavior in the field and to design mass production plan of the parasitoid for the biological control of economic insect pests.1. Effects of food quality and feeding frequency on longevity of M. pulchricornis (Hymenoptera: Braconidae)To investigate effects of the carbohydrate food on adult Meteorus pulchricornis, the longevity and feeding time were observed on sugar diets in different concentrations (0, 10, 30, 50, and 70% (w/v) with glucose : fructose : sucrose = 1:1:1). At the presence of host larvae, there was a significant effect of sugar concentrations on M. pulchricornis longevity. When compared with longevity of water-fed controls, female longevity was significantly enhanced at all sugar concentration used. Females fed on sugar diets lived three times longer than water-fed parasitoids. But there were non-linear relationship between longevity and sugar concentrations in that the longevity did not increase linearly with increasing sugar concentrations. Maximum longevity was observed for parasitoid fed on 30% (w/v) sugar diet, whereas there were no distinct differences in the sugar concentrations of 10%, 50%, and 70%. Compared to parasitoids deprived of host larvae, the longevity of wasps was decreased. Using 30% (w/v) sugar solution as the adult food a feeding regime was set up as no food, water only, one-time feeding (i. e., on the first day of experiment), feeding once every two days, once every three days, once every four days, and continuous food access. In host's absence, the average longevity of M. pulchricornis obviously depended on feeding frequency. Females deprived of any food lived an average of 8.25±0.15 days. Females fed on other frequencies largely extended their lifespan. There was a linear relationship between longevity and feeding frequency, in that the longevity increased significantly with feeding frequency. Interestingly, the highest female lifespan was observed for parasitoid fed continuously on 30% (w/v) sugar diet (46.37±1.69 days), which is 5 times more than the average lifetime of unfed parasitoid.2. Effects of food quality and feeding frequency on fecundity of M. pulchricornis (Hymenoptera: Braconidae)Female parasitoids began oviposition at the second day of eclosion, and thereafter increased egg-laying schedule. Daily oviposition peaked at 4th through 9th day, and thereafter declined slowly in next few days, and then decreased markedly. Most eggs were laid in the first 15 days after adult eclosion, but the parasitoid fed on 30% sugar diet continuously oviposited for up to 25 days. Daily egg-laying schemes were similar across different feeding diets. Parasitoids fed on 30% sugar diet achieved not only the longest oviposition, but also the highest daily-laid eggs (15 eggs). It is obvious that sugar concentration had a significant effect on both oviposition period and fecundity. Compared with water-fed controls, both oviposition period and fecundity were significantly enhanced at all sugar diets provided.The fecundity of M. pulchricornis obviously depended on feeding frequencies. The feeding frequency was set up as described above. Each individual was fed with a droplet (5ul) of 30% (w/v) sugar diet. Compared with the females deprived of food, females fed by different frequencies markedly increased their fecundities. However, no linear correlation was detected between fecundity and the feeding frequency. The highest fecundity was observed for parasitoids fed continuously, which was two times greater than the water-fed parasitoids and seven times greater than the unfed parasitoids. The parasitoids deprived of food or fed on water had shortest oviposition period (four and nine days respectively), whereas wasps with continuous access to food oviposited for as long as 21 days. There were no significant differences in fecundity amongst parasitoids with other feeding frequencies.3. Effects of supplementary food on behaviors of M. pulchricornis (Hymenoptera: Braconidae)Behaviors of M. pulchricornis were composed of seven components: flying, walking, grooming, pointing, standing still, feeding, and attacking. The parasitism varied enormously with sugar diets for the parasitoid. Most parasitoids parasitized hosts on the 2nd day after eclosion, and then parasitism was increased to the highest level from third to sixth day. From then on parasitism decreased drastically with some minor increases. Parasitoids fed on 30% sugar diet had longest parasitization time and the highest parasitism. Duration of first feeding of M. pulchricornis depended significantly on sugar concentrations with a significant linear correlation (R~2 = 0.9843, P＜0.05) between them. Feeding period was twice for parasitoids fed on 70% sugar diet (161.3±4.8 s ) as long as fed on water (70.1±3.5 s) .The proportion of parasitoids with second feeding was decreased with sugar concentrations, by 55.8%, 53.4%, 40.7%, 43.9%, 41.4% with respect to sugar diets 0, 10, 30, 50, and 70% (w/v) with glucose : fructose : sucrose = 1:1:1, even though no linear correlation between them was not found.