POPULATION BIOLOGY AND SPECIES INTERACTIONS IN HERBIVOROUS INSECTS

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An herbivorous lady beetle Epilachna niponica exhibited a high stability of population densities in terms of host plant abundance. Field experments revealed that reproductive females resorbed eggs in the ovary in response to host plant deterioration. Also, females selected oviposition site carefully, by laying eggs on plants with less egg load. These specified oviposition tactics resulted in a temporal resource tracking of populations, through density-dependent reduction in realized eggs per female. Lifetime fitness of offspring decreased with increasing egg density. This implies that oviposition on plants with less egg density improves lifetime reproductive success of an ovipositing female. Egg resorption could have adaptive significance when offspring fitness drops considerably due to resource deterioration late in the reproductive season or habitat disturbance such as inundation. It slso enhances a chance of future oviposition in the second reproductive season, through increasing subsequent survival of egg-resorbed females. Consequently, the oviposition behavior of reproductive females in time and space is highly correlated with lifetime fitness of their offspring.