Does the Number of Diapausing Eggs Laid on Bark Affect the Population Dynamics of the Spider Mite Panonychus mori?

Abstract

We studied the relationship between number of diapausing eggs produced by the spider mite Panonychus mori and the subsequent population trend for a period of 3 years. Panonychus mori showed a single population density peak on its host plant moonseed, Cocculus trilobus. The position and height of this peak were correlated with the density of diapausing eggs around the moonseed leaf buds produced the winter before. In 1994 the density of diapausing eggs measured in February was 4.3/bud, which was 6-14 times higher than the density of diapausing eggs for the same period in 1995 (0.3/bud) and 1996 (0.7/bud). The subsequent population density peak in 1994 occurred in mid June and was about 2.5 times higher than the peaks in 1995 and 1996, which both occurred early September. Thus, the present study showed a positive correlation between the density of diapausing eggs on the host plant and the start and the extend of the population increase the next growing season. Predators associated with the spider mite population were phytoseiid mites, especially Amblyseius eharai was well synchronized with the spider mite density in 1994. Field observations revealed that P. mori produced diapausing eggs in response to short photoperiod in early October each year, which corresponded with the timing predicted by the critical photoperiod around 13 h at 18 degrees C, as assessed in laboratory trials. Diapause ended by early April when egg hatchability attained about 50% and eggs took 9 days to hatch at 25 degrees C and a 16L:8D photoperiod. Hatching in early April was twice faster than in late February.

Life cycles and interactions in spider mites (Acari: Tetranychidae) on dwarf bamboo,Sasa senanensis(F. & S.) (Poaceae), in Japan

“…characterized by an inability to hatch even when kept at 25°C and under a 16L:8D photoperiod (Veerman, 1985;Gotoh et al, 2006) and by distinct changes in the egg color and size (Table 8). The body colors of female-diapausing species completely changed at 31.8 + 0.61 days (mean + S.E., n = 35) after emergence of adults for Ap.…”

“…Non-diapausing eggs hatched within 10 days under these conditions, whereas diapausing eggs did not. Thus, eggs that remained without hatching for longer than 10 days were regarded as diapausing eggs in the present study (Gotoh, 1986b;Gotoh et al, 2006). In addition, diapausing eggs were characterized by a distinct change in color and size from non-diapausing eggs (Table 8).…”