Temperature-Dependent Development Models Describing the Effects of Temperature on the Development of the Fall Armyworm Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae).

The fall armyworm Spodoptera frugiperda (J.E. Smith) is an economically important pest that recently invaded Africa and Asia; however, information regarding its biological capacity to establish itself in newly invaded environments is largely unknown. We investigated the effects of temperature on the development and survival of the invaded populations of S. frugiperda and selected mathematical models to evaluate its development in a new environment. S. frugiperda exhibited optimum survival and growth at temperatures between 28 °C and 30 °C. The lower and upper thermal thresholds for the egg-to-adult life cycle were 13.51 °C and 34.13 °C, respectively. We compared seven mathematical models and found that the Shi model was the most suitable for describing the temperature-dependent development rate of S. frugiperda. Therefore, the Shi mathematical model may be used to predict both the occurrence of particular developmental stages and the geographic distribution to implement measures for the management of S. frugiperda in agricultural fields.

Impact of Rice and Potato Host Plants Is Higher on the Reproduction than Growth of Corn Strain Fall Armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae).

The fall armyworm (FAW), Spodoptera frugiperda, is an invasive pest species that has recently increased its range in most African and Asian countries, causing significant losses to crop yields, especially corn. To develop effective management strategies, it is particularly important to study the biology of FAW in various crops. Here, we utilized the age-stage, two-sex life table to examine the development, survival, and reproduction rate of the corn strain FAW on three different host plants: corn, rice, and potato. The corn strain FAW successfully completed its life cycle in rice and potato, as well as corn plants. However, the growth, developmental time, survival, and reproduction rate differed among the three host plants. The preadult survival rates in corn, rice, and potato were 92%, 81%, and 77%, respectively. Similarly, mean generation time was significantly shorter in corn (35 days), followed by rice (41 days) and potato (42 days), indicating more generations in corn. Interestingly, the net reproduction rate varied greatly among the three host plants. In corn-fed FAW, the net reproduction rate was 472 offspring per individual, whereas, in rice and potato crops, the rates were only 213 and 86 offspring per individual, respectively. Our results suggest that alternative host plants, such as potato and rice, have more effect on reproduction than the growth of corn strain FAW. These results may be useful in predicting the population dynamics of FAW and understanding the potential damage to crops, thus contributing to an appropriate management strategy in the newly FAW-invaded agricultural ecosystems.

Genetic Relationship of Fall Armyworm (Spodoptera frugiperda) Populations That Invaded Africa and Asia.

The fall armyworm, Spodoptera frugiperda, is an important agricultural pest native to tropical and subtropical regions of the Western Hemisphere, and has invaded Africa and further spread into most countries of Asia within two years. Here, we analyzed the genetic variation of invaded populations by comparing the nucleotide sequences of two genes: the nuclear Z-chromosome linked gene triose phosphate isomerase (Tpi) and the mitochondrial gene cytochrome oxidase subunit I (COI) of 27 specimens collected in Africa (DR Congo, Tanzania, Uganda, and Zimbabwe) and Asia (Bangladesh, Korea, Nepal, and Vietnam). The results revealed that 25 specimens were from a heterogeneous hybrid (Tpi-corn strain and COI-rice strain; Tpi-C/COI-R) of the corn strain male and rice strain female, but two specimens were from a homogenous corn strain (Tpi-corn strain and COI-corn strain; Tpi-C/COI-C). The further analysis of the fourth exon and the fourth intron sequences of the Tpi gene identified at least four subgroups of the corn strain. These four genetic subgroups were identified in Africa and Asia, suggesting no significant genetic change due to the rapid migration within two years. Our study provides essential information for understanding the genetic diversity of fall armyworm in new habitats.