Browsing by Author "Ge, Feng"

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Comparison of Thermal Performance Equations in Describing Temperature-Dependent Developmental Rates of Insects: (I) Empirical Models
(2015-12) Shi, Pei-Jian; Reddy, Gadi V. P.; Chen, Lei; Ge, Feng
Temperature greatly affects the developmental duration of insects at their different stages, and many mathematical models exist for describing their temperature-dependent developmental rates. It is important to choose a suitable model to predict outbreaks of pest insects under climate change. However, previous comparisons among these models were usually based on a single species. In the present study, we compared the six nonlinear models (the BriÃ©re-1, BriÃ©re-2, Lactin, Performance-2, beta, and Ratkowsky models) based on the goodness of fit and the trade-off between the modelâ€™s goodness of fit and structural complexity, using 10 temperature-dependent developmental rate datasets on insects to make the conclusions general. We found that the square root model (i.e., the Ratkowsky model) fitted all datasets well, and the curve shape produced by this model also approximates the curve shape of thermodynamically based mathematical models. The square root model was originally derived to be applicable to the growth rates of bacteria, and until now it has been generally ignored in entomology. We were mainly concerned with the predicted results obtained by using this model on observations of temperature-dependent developmental rates. We found that the square root model described well the pooled developmental rates in the low-, mid-, and high-temperature ranges, and we believe that it merits wider use in entomology.
Nonparametric Estimation of Interspecific Spatio-Temporal Niche Separation Between Two Lady Beetles (Coleoptera: Coccinellidae) in Bt Cotton Fields
(2015-07) Lu, Zeng-Bin; Shi, Pei-Jian; Reddy, Gadi V. P.; Li, Lin-Mao; Men, Xing-Yuan; Ge, Feng
Predaceous lady beetles are important natural enemies of many insect pests in agro-ecosystem. The altered agricultural practices associated with widespread adoption of Bt cotton may have potential effects on the spatio-temporal patterns of predaceous lady beetles, as the composition and abundance of nontarget sucking pests have been changed in Bt cotton fields. In the current study, the spatio-temporal patterns of two important lady beetles, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) and Propylea japonica (Thunberg) (Coleoptera: Coccinellidae), were surveyed in Bt cotton fields. A nonparametric method associated with Monte Carlo tests was used to address and test whether niche segregation occurred between H. axyridis and P. japonica. The results showed that the dominant region occupied by P. japonica was toward northeast across the season, whereas H. axyridis had higher presence to the southwest. The temporal patterns of H. axyridis and P. japonica also differed significantly, and the highest levels of each species occurred in different locations from each other on each sampling date in the same Bt cotton fields. In total, there were strong spatio-temporal separation patterns between these two species in Bt cotton fields. These spatio-temporal patterns may produce complementary impacts on prey, and this in turn could be used to strengthen the biological control of insect pests by these two lady beetles.
The seesaw effect of winter temperature change on the recruitment of cotton bollworms Helicoverpa armigera through mismatched phenology
(2015-12) Reddy, Gadi V. P.; Shi, Pei-Jian; Hui, Cang; Cheng, Xiaofei; Ouyang, Fang; Ge, Feng
Knowing how climate change affects the population dynamics of insect pests is critical for the future of integrated pest management. Rising winter temperatures from global warming can drive increases in outbreaks of some agricultural pests. In contrast, here we propose an alternative hypothesis that both extremely cold and warm winters can mismatch the timing between the eclosion of overwintering pests and the flowering of key host plants. As host plants normally need higher effective cumulative temperatures for flowering than insects need for eclosion, changes in flowering time will be less dramatic than changes in eclosion time, leading to a mismatch of phenology on either side of the optimal winter temperature. We term this the “seesaw effect.” Using a long-term dataset of the Old World cotton bollworm Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) in northern China, we tested this seesaw hypothesis by running a generalized additive model for the effects of the third generation moth in the preceding year, the winter air temperature, the number of winter days below a critical temperature and cumulative precipitation during winter on the demography of the overwintering moth. Results confirmed the existence of the seesaw effect of winter temperature change on overwintering populations. Pest management should therefore consider the indirect effect of changing crop phenology (whether due to greenhouse cultivation or to climate change) on pest outbreaks. As arthropods from mid- and high latitudes are actually living in a cooler thermal environment than their physiological optimum in contrast to species from lower latitudes, the effects of rising winter temperatures on the population dynamics of arthropods in the different latitudinal zones should be considered separately. The seesaw effect makes it more difficult to predict the average long-term population dynamics of insect pests at high latitudes due to the potential sharp changes in annual growth rates from fluctuating minimum winter temperatures.