The success of mating disruption using synthetic sex pheromones depends not only on preventing mating, but also on delayed mating in the target insect. Using the rice leaffolder moth, Cnaphalocrocis medinalis (Guenée), we determined the effect of increased age at mating imposed on males only (male treatment), females only (female treatment),or on both sexes simultaneously (both sexes treatment). These increased age treatments had a negative effect on the percentage of mating, the total number of eggs, and the hatchability. The female reproductive performance in C. medinalis was decreased with increased moths' age. The both sexes treatment had the most potent negative effect on reproductive performance. Longevity of mated moths and duration of the preoviposition period in C. medinalis were not significantly different among these increased age treatments. The underlying mechanisms causing a decline in female reproductive performance of C. medinalis when increased age was imposed on males versus females and the potential of using mating disruption strategies to control the populations in paddy fields are discussed.
The development of 4th stadium Psacothea hilaris larvae under various feeding and starving regimens was investigated to determine whether there is a threshold weight for metamorphosis. In larvae fed ad libitum, 56% of individuals spent a mean of 13 d in the 4th stadium and 18 d in the 5th stadium before pupation, whereas the rest remained in the 4th stadium for 24 d and pupated. When starved upon ecdysis to the 4th stadium, no larvae molted to the 5th stadium and most eventually died without pupation. In contrast, when larvae were fed for 1 d and then starved, 47% prematurely metamorphosed into small pupae after a mean of 18 d in the 4th stadium. Pupation success from the 4th stadium increased as the feeding period was extended, reaching 97% in the larvae that had fed for four days. All these pupae gave rise to small but morphologically normal adults. The relationships between the weight changes of experimental larvae during starvation and their pupation success suggested the threshold weight for metamorphosis to be 180 mg. The adaptive significance of premature pupation in starved P. hilaris is discussed as a life history strategy under unpredictable food conditions for larval growth.
Cold hardiness of eggs and neonate larvae of the yellow-spotted longicorn beetle, Psacothea hilaris (Pascoe) was examined using six geographical populations in Japan. Particular attention was paid to cold hardiness of eggs and neonate larvae of the subtropical population (Ishigaki), because the east Japan populations are considered to have been introduced from a subtropical area, and the overwintering stage in the east Japan populations is incidentally shifted from the original mature larval stage to the egg or neonate larval stages. When the eggs were exposed to low temperatures for 1 h, the decrease in hatchability became signi®cant at ±12°C in the southernmost two populations (Ishigaki and Naze), and at ±16°C in the northern populations. After 1 h exposure to ±20°C, few eggs could hatch in the Ishigaki population, whereas 27±55% of the eggs survived in the northern populations. Pre-chilling of the eggs at 10°C for 10 days enhanced the cold hardiness in all populations. This effect was particularly distinct in the subtropical population; the eggs of the Ishigaki population became as cold hardy as those of the northern populations after acclimation. These results suggest that the subtropical population is capable of establishing itself in east Japan, where the winter is cold.
Recent climate warming has affected some life‐history traits of insects, including voltinism and body size. The magnitude of changes in these traits may differ latitudinally within a species because of the differing lengths of season available for growth. The present study aims to estimate the change in voltinism of the lawn ground cricket, Polionemobius mikado (Shiraki) (Orthoptera: Trigonidiidae), over the last four decades by comparing the body size between adults collected from a wide range of latitudes in Japan in recent years (2015–2017) and those collected four decades ago (1969–1976). The body size of adults collected in recent years showed a latitudinal saw‐tooth cline, in the same way as body size did four decades ago, and the cline shifted northward over the last four decades: In 2015–2017, the body size decreased slightly with increasing latitude from 31°N to 36°N, and then increased to 40°N, and again decreased from 40°N to 44°N. Comparison of the body size between recent years and four decades ago revealed that the body size has decreased significantly at the middle latitudes (36–40°N), suggesting that the proportion of smaller bivoltine individuals there has increased over the last four decades. The sum of effective temperatures for postdiapause embryonic development at around 36°N in recent years was comparable to that at 31–35°N four decades ago, at which P. mikado populations were bivoltine. Taken together, these findings suggested that the latitudinal range suitable for the bivoltine life cycle of P. mikado has expanded northward over the last four decades because of climate warming. This is the first report that shows that a decrease in body size can be caused by climate warming via an increase in voltinism.
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