Population Dynamics and the Effects of Temperature on the Eggs of theSeawater-dispersed Stick Insect Megacrania tsudai (Phasmida: Phasmatidae)

摘要

Although the stick insect cannot fly, its eggs are dispersed by seawater, which allows the species todistribute itself widely via the ocean. The life history of this non-volant insect thatestablishes settlements by egg dispersal remains poorly understood. We aimed to clarifythe population dynamics and effects of temperature on the eggs of through field observation in near the northern limits of the distribution andlaboratory experiments. In the wild, all instars appeared over a period of several months,with a larger proportion of first instars emerging from December to March, and a greaternumber of adults being observed from June to August. Laboratory experiments showed thatthe hatching rate of was not different between conditions of 25and 30°C, whereas it was significantly lower at 20°C. The egg-development period wasshorter when eggs were maintained under high temperature conditions, and longer for eggskept at 20°C. The effective cumulative temperature was estimated as 1561.5-2000.0°C, andthe developmental zero was estimated as 12.2-13.9°C. The peak appearance of the firstinstar in the laboratory, which was used to obtain an estimate for the effectivecumulative temperature and peak appearance of adults in the wild, was not entirelyaccurate because the peak appearance of the first instars in the wild was not consistentlyobserved when the estimation indicated that they should appear. is a univoltine near the northern limit of its distribution, and temperature hasa strong effect on its egg development. Our estimation of population dynamics bylaboratory experiments did not exactly predict what was observed in the field and it maybe controlled by other factors. However, our findings indicate that the limiting factor ofthe distribution of this species is likely the effect of temperature on egg hatching.