Post-diapause development and multimodal oviposition activity of arrowhead scale, Unaspis yanonensis (Homoptera: Diaspididae) and its modeling

The longevity and fecundity of overwintered Unaspis yanonensis Kuwana (Homoptera: Diaspididae) were examined at constant temperature 24°C, and its periodical oviposition activity was modeled. Adult females collected in early November showed abnormal post-diapause development; prolonged pre-oviposition period, not producing progenies and much lower fecundity. All females collected from early December through early March showed normal post-diapause development and had ≈20 d of pre-oviposition period and ≈80 d of longevity. Overwintered U. yanonensis showed a periodical oviposition activity with a maximum 4 times of oviposition cycle during their life time, and the pattern was flexibly fitted to a 4-peak Gaussian function. The average peak timings (parameter a) occurred at 5.5, 25.2, 41.6, and 56.4 d for the 1st, 2nd, 3rd, and 4th peak from the start of oviposition, respectively. The height of the peaks (parameter b) gradually decreased from 14.9 for the 1st peak to 5.0 for the 4th peak. The parameter values of the 4-peak equation were successfully converted to degree-days unit with a lower threshold temperature 13°C for field validation. The model predicted the 1st oviposition peak of overwintered U. yanonensis very well (≈282 DD from 1 January), while showed large discrepancy with actual data in the later peak period. A 3-modal oviposition curve that includes the individual variations of oviposition activity of U. yanonensis females with removing the 4th cycle showed a better shape fitting ability in the later peak period. Further, application and improvement of the multi-peak model were discussed.