| 概要 |
The primary aim of evolution ecology has been to explain the divergent patterns in life-history among and within animal species, Insect parasitoids are one of the most diverse groups of insects with d...ivergent life-history strategines, and have been shown as an excellent test organism in evolutionary ecology . Also, because parasitoids often play an important role in suppressing pest populations in agriculture, revealing the life-history characteristics of parasitoids has been the primary approach to assess their importance and effectiveness in biological control of agricultural pests. Since the environment is instable in time and space, parasitoids have life history traits that are adapted to the environmental changes. Itoplectis naranyae Ashmead(Hymenoptera : Ichneumonidae)is a solitary endoparasitoid wasp that attacks a variety of lepidopterous pupae. This parasitoid is widespread and abundant in rice paddies of japan and other East Asia, where it is an important natural enemy of lepidopteran pests such as rice leaf folder. I.naranyae is typically synovigenic and produces relatively large yolk-rich enggs throughout the relatively long span; adult females must gain nutrients to sustain their activity and egg production throughout the lifetime. I.naranyae is a destructive host-feeding species; host feeding allows the female to nutrients for egg production, but hosts fed on become unsuitable for oviposition. The present thesis aims to examin: (1) the cost and benefit of different food types in adult diet of female I.naranyae; (2) the effect of adult body size on reproductive traits; (3) the factors restrict the development and nutrient carried over before adult emergence. Finally, the interaction of these lifetime traits that lead to a variable life-history strategy of I.naranyae is discussed. The longevity and fecundity of female I.naranyae were enhanced when feeding on carbohydrates; they lived more than 1.5 months with a sugar source, but no more than two weeks without it. Dissecting experiments revealed that both the egg production and maturation were improved when sufficient carbohydrates were given. The fecundity also uncreased host fluids were artificially provided. The egg production however was best enhanced when both host- and sugar feedings were allowed. In addition, the females produced larger eggs when food was sufficiently available. Female I.naranyae offered with host blood only produced relatively smaller eggs than those with carbohydrates in their diet, indicating it can modify the investment to each egg and regulate reproductive output in response to different food conditions. Curiously, the longevity of I.naranyae was shorter in the presence of hosts than those deprived of hosts, indicating the presence of a trade-off between reproduction and life expectancy, i.e., cost of reproduction. Body size of female I.naranyae positively affected their lifetime traits from different aspects. The longevity increased as the body size increased, no matter food source types or the availability of host pupae. Larger females carried more eggs in their ovary. Moreover, the body size positively affected on the size of eggs produced. Larger females tend to produce more female offspring. Although body size itself has no effects on the fitness of their offspring, larger female offspring. Although body size itself had no effects on the fitness of their offspring, larger eggs required shorter developmental time, suggesting production of large eggs is advantageous under larval competition. In this dissertation, I employed two indexes for body size of I.naranyae, which are body weight at parasitoid emergence and forewing length. Although these two parameters were significantly correlated with each other, the effects were not. The forewing length seemed to be a better predictor of body size of females I.naranyae; while in the study of fecundity and egg size, the body weight at emergence was better. Large size benefits parasitoids directly in competing fitness functions, such as survival and reproduction, but it is also assumed that large size would have negative impacts on some life-time traits, such as energy consumption, mobility and development. Forewing length is directly correlated with ability and consume of flight and other daily activities, so it would be more suitable in the test of life span. On the other hand, the body weight of an individual can directly reflect capability of resource acquiring and/or storing. Hence, it may be more suitable in the research of nutrition acquisition and allocation of parasitoids. The egg size of I.naranyae is variable, is positively correlated with hatching time and the size of the hatching larva. Becouse the super- and multi-parasites are common the field, faster development may be the superiority to overcome the competition of both inter- more in each egg. Life-history strategies of I.naranyae are complex and flexible, and they are affected by both internal (i.e. body size egg production, age) and external factors (i.e. nutrition both prey and non-prey, host availability, environment). These factors combine together and interact with each other to influence the traits throughout life time. Such flexible strategies would allow I.naranyae to cope with variable food conditions, competitive environments, and different types of hosts they develop.続きを見る
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