Matabaro Joseph Malekera

Both Spodoptera frugiperda and Spodoptera litura are highly invasive pest species that can attack agricultural crops in new areas, causing high economic damage. The survival of invasive species is highly affected by their ability to adapt to new environments as well as climate change. Rapid cold hardening (RCH) and rapid heat hardening (RHH) play important roles in ecological adaptation and survival under fluctuating temperature conditions. To compare the rates of survival, development, and reproduction between S. frugiperda and S. litura , the effects of RCH (5°C for 12 h followed by −10°C for 2 h) and RHH (35°C for 12 h followed by 41°C for 2 h) treatments were determined on the 3rd or 6th instar larvae of both species. The results showed that treatments of CS (−10°C for 2 h) and RCH conditions into the 3rd instar larvae of both S. frugiperda and S. litura increased the survival rates at 23.2% and 24.0%, respectively. Treatments of HS (41°C for 2 h) and RHH conditions into the 3rd instar larvae of both species increased the survival rates at 30.6% and 26.7%, respectively. However, similar thermal hardening conditions treated into the 6th instar larvae did not increase the survival rates in both species. Thermal stress experienced at later larval instars negatively minimized the pupal weight and subsequent reproductive parameters of both species. The findings showed that S. frugiperda had a higher thermal plasticity set off by rapid thermal hardening than S. litura . Our results suggest that S. frugiperda retains the ability to enhance rapid thermal tolerance to cold winters and hot summers in the newly invaded habitats as well as climate change conditions.

This study investigated the spatiotemporal dynamics of climate potential productivity and its correlation with changes in maize productivity in four agroclimatic zones of the Democratic Republic of the Congo (DRC) using Thornthwaite Memorial models and Mann–Kendall Trend Analysis from 1960 to 2024. Climate potential productivity showed contrasting trends between agroclimatic zones. In the Haut-Katanga and Tchuapa zones, the precipitation showed a strong positive relationship with climate potential productivity, emphasizing that water availability from rainfall is the primary driver of agricultural productivity. In Kongo Central and South Kivu zones, both precipitation and temperature indicated a positive relationship with climate potential productivity, highlighting that agricultural productivity in these zones, is highly sensitive to tropical climate variability. The climate resource utilization efficiency demonstrates markedly divergent trends across agroclimatic zones, possibly due to distinct agroclimatic conditions. Climate resource utilization efficiency indicated a fluctuating positive relationship with per-unit maize yield in the four agroclimatic zones. During the studied period, maize yield declined by 19.68%, 17.48%, 13.40%, and 15.65% in the agroclimatic zones of Haut-Katanga, Kongo Central, South Kivu, and Tchuapa, respectively. These findings can help in mitigating climate-related risks and contributing to agricultural resilience and food security.

In 2016, the fall armyworm (FAW), Spodoptera frugiperda, invaded western Africa and rapidly spread in sub-Saharan Africa, causing significant losses in yields of corn, a major food crop in Africa. Although the Democratic Republic of the Congo (DRC) is a large corn-growing country, the impact of FAW has not been investigated. This study was designed to expand investigations on the genetic diversity of FAW populations in the DRC. We collected FAW individuals from eight provinces across the country, for analysis of genetic variation. Based on the partial sequences of both mitochondrial cytochrome oxidase subunit I (COI) and nuclear triosephosphate isomerase (Tpi) genes, we compared polymorphic features of the COI haplotype and Tpi single nucleotide polymorphisms. The results revealed that most (84%) of the analyzed individuals were heterogeneous hybrids Tpi-corn/COI-rice (Tpi-C/COI-R), whereas 16% were homogenous Tpi-corn/COI-corn (Tpi-C/COI-C). Further analysis of the fourth exon/intron sequences of the Tpi gene identified two subgroups, TpiCa1 and TpiCa2, constituting 80% and 20%, respectively, of the collected individuals. Analysis of genetic variation among native and invasive populations indicated significant genetic differences (10.94%) between the native American and DRC populations, whereas both the DRC and African populations were genetically closer to Asian than American populations. This study provides important information on FAW genetic diversity in the DRC, which can be used for effective management of FAW.

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.

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.

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.