Improving the degree-day model for forecasting Locusta migratoria manilensis (Meyen) (Orthoptera: Acridoidea) - PubMed (original) (raw)

Improving the degree-day model for forecasting Locusta migratoria manilensis (Meyen) (Orthoptera: Acridoidea)

Xiongbing Tu et al. PLoS One. 2014.

Abstract

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°C did not influence locust development rate. Hence, the additional heat provided by temperatures above 32°C did not add to the total heat units acquired by the insects, according to the traditional DD model. Instead, temperatures above 32°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°C failed to oviposit. Hence, temperatures lower than 21°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.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1

Figure 1. The mimicked temperatures in different growth chambers.

Seven locations in China modeled in this study, Baiquan (BQ), Chengde (CD), Tumotezuoqi (TM), Wenan (WA), Rongan (RA), Qiongzhong (QZ), and Qiongshan (QS). Mean temperatures were obtained from (

http://cdc.cma.gov.cn/home.do

) throughout the growing season for each location based on an estimated lower thermal threshold for development of 14.2°C for Locusta migratoria manilensis Meyen. Growth chamber temperatures in Chengde changed daily while in other locations changed every 10 d.To simulate variable environmental temperatures, we designed a variable range of ‘±5°C’ for the daily 24-h temperature change.

Figure 2

Figure 2. Developmental duration of locust eggs and nymphs at different constant temperatures.

Each line represents the mean developmental duration of the same developmental stage at different constant temperatures.

Figure 3

Figure 3. Relationship between temperature and locust (eggs, nymphs, and oocytes) developmental rate.

Oocytes developmental rate based on calculating the pre-ovipositing period at 22, 23, 24, 27, and 30°C, while dashed lines show theoretical extension of regression lines to x-axis. The points where the lines intersect the x-axis represent the theoretical low temperature threshold (LTT) for development egg, and nymph was ∼14°C, while for oocyte was ∼18°C.

Figure 4

Figure 4. DD for locusts on April 12, 2011, in Langfang based on the integral calculation method.

24-hours ground temperature was recorded by HOBO Pro v2 logger which were used to model temperature change curve by Matlab R2011b. ‘a’ & ‘b’ represent the intersect points between y = 14.2 and the curve. The shade area was the DD for locust development in this day.

Figure 5

Figure 5. Overflow DD for locusts on July 9, 2011, in Langfang based on the integral calculation method.

24-hours air temperature was recorded by HOBO Pro v2 logger which were used to model temperature change curve by Matlab R2011b. ‘a’ & ‘b’ represent the intersect points between y = 32 and the curve. The shade area was the overflow DD for locust development in this day.

Figure 6

Figure 6. DD calculation based on mean, max-min, 24-hours temperature data.

24-hours temperature data was shown in Fig. 4. Minimum, mean and maximum temperature of this day was about 12.1, 14.0 and 15.4°C. (A) DD calculating based on daily mean temperature. (B) DD calculating based on maximum-minimum temperature. (C) DD calculating based on 24-hours temperature, it should be calculated as: ∑(T-14.2)/24, not the same as 24-hours integral calculation in Fig. 4.

Figure 7

Figure 7. Standard DD calculating for locust accomplishing full generations based on life history of L. m. manilensis and temperature changes in Langfang, 2011.

In field, we predicted hatchlings emergence mostly by air temperature as we lacked ground temperature data, so the DD was 1566 DD when only used air temperature (the dashed line). Instead, when we used ground temperature (the solid line) to calcualte DD for eggs, the total DD for migratory locust was 1437 heat units based on 24-hours integral calculation. (A) Overflow DD was 38 heat units from 28th May to 5th September. (B) Useless DD for females egg-laying was 128 heat units from 8th September to 10th October (these days were ovipositing periods for females, but temperature lower than 21°C).

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This article was supported by the earmarked fund for China Agriculture Research System (CARS-35-07) and the Special Fund for Agro-scientific Research in the Public Interest, 201003079. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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