Improving the Degree-Day Model for Forecasting Locusta migratoria manilensis (Meyen) (Orthoptera: Acridoidea): e89523

• Published in: PloS one 2014-03, Vol.9 (3)
• Main Authors: Tu, Xiongbing, Li, Zhihong, Wang, Jie, Huang, Xunbing, Yang, Jiwen, Fan, Chunbin, Wu, Huihui, Wang, Qinglei, Zhang, Zehua
• Format: Article
• Language: English
• Subjects: Acridoidea; Locusta migratoria manilensi; Orthoptera
• ISSN: 1932-6203
• DOI: 10.1371/journal.pone.0089523

The degree-day (DD) model is an important tool for forecasting pest phenology and voltinism. Unfortunately, the DD model is inaccurate, as is the case for the Oriental migratory locust. To improve the existing DD model for this pest, we first studied locust development in seven growth chambers, each of which simulated the complete growing-season climate of a specific region in China (Baiquan, Chengde, Tumotezuoqi, Wenan, Rongan, Qiongzhong, or Qiongshan). In these seven treatments, locusts completed 0.95, 1, 1.1, 2.2, 2.95, 3.95, and 4.95 generations, respectively. Hence, in the Baiquan (700), Rongan (2400), Qiongzhong (3200), and Qiongshan (2400) treatments, the final generation were unable to lay eggs. In a second experiment, we reared locusts for a full generation in growth chambers, at different constant temperatures. This experiment provided two important findings. First, temperatures between 32 and 42 degree C did not influence locust development rate. Hence, the additional heat provided by temperatures above 32 degree C did not add to the total heat units acquired by the insects, according to the traditional DD model. Instead, temperatures above 32 degree C represent overflow heat, and can not be included when calculating total heat acquired during development. We also noted that females raised at constant 21 degree C failed to oviposit. Hence, temperatures lower than 21 degree C should be deducted when calculating total heat acquired during adult development. Using our experimental findings, we next micmiked 24-h temperature curve and constructed a new DD model based on a 24-h temperature integral calculation. We then compared our new model with the traditional DD model, results showed the DD deviation was 166 heat units in Langfang during 2011. At last we recalculated the heat by our new DD model, which better predicted the results from our first growth chamber experiment.