The effect of temperature on the development and reproduction of Busseola fusca (Lepidoptera: Noctuidae)

Consolidation of temperature-dependent toxicity and thermoregulatory behavior into risk assessments of insecticides under thermal scenarios: A prospective study on Eremias argus

In this study, the temperature-dependent chemical toxicity of three insecticides and the resulting thermoregulatory (TR) behavior of the lizard Eremias argus have been consolidated into the current risk assessment framework. According to acute dermal toxicity assays, an increase of ambient temperature from 15 °C to 35 °C decreased the acute dermal toxicity of beta-cyfluthrin (BC) but increased the toxicity of chlorpyrifos (CPF). The toxicity of avermectin (AVM) did not show significant temperature-dependent responses. Based on thermal preference trials, lizards changed their body temperature via TR behavior to adaptively reduce toxicity under sub-lethal doses, which can be understood as a "self-rescue" behavior attenuating lethal effects. However, the risk quotient indicated that the effectiveness of this "self-rescue" behavior is limited. Metabolomics analysis showed that six different metabolites (i.e., creatine, glutamate, succinate, N-acetylaspartate, acetylcholine, and lactate) contributed to TR behavior changes. Biochemical assays and insecticide residue results demonstrated that the temperature-dependent toxicity of BC, CPF, and AVM affected lizards in the three aspects of biotransformation, oxidative stress, and neurometabolic interference. This work clarifies the ecotoxicological impacts of representative insecticides on reptiles from toxicological understanding to risk relevance. This knowledge may improve ecological predictions of agrochemical applications in the context of global climate change.

Developmental Differentiations of Major Maize Stemborers Due to Global Warming in Temperate and Tropical Climates

While many insects are in decline due to global warming, the effect of rising temperatures on crop insect pests is uncertain. A capacity to understand future changes in crop pest populations remains critical to ensure food security. Using temperature-dependent mathematical models of the development of four maize stemborers in temperate and tropical regions, we evaluated the potential impacts of different climate change scenarios on development time. While recognizing the limitations of the temperature-dependent development rate approach, we found that global warming could either be beneficial or detrimental to pest development, depending on the optimal temperature for the development of the species and scenarios of climate change. Expected responses range from null development to 1.5 times faster development than expected today. These results suggest that in the medium term, the studied species could benefit from global warming with an accelerated development, while in the long term, their development could either be delayed or accelerated, which may impact their dynamics with implications on maize cultivation.

Temperature-Dependent Demography of Two Geographically Isolated Populations of Sesamia cretica (Lepidoptera: Noctuidae)

The pink stem borer, Sesamia cretica Lederer is considered as the main insect pest of maize and sugarcane worldwide. Reproductive and life table parameters of two populations of S. cretica were studied at 10 constant temperatures ranging from 12 to 36 (±1)°C, 50 ± 10% RH and a photoperiod of 0:24 (L:D) h for the larval stage and 16:8 (L:D) h for the other stages. At 12°C, no eggs hatched and at 15, 35, and 36°C only the incubation period was completed. The longest (135.81 and 156.49 d) and shortest (49.61 and 52.09 d) female life span were observed at 20 and 32°C for the Varamin and Rey populations, respectively. The highest (181.66 and 180.94 eggs/female) and lowest (13.40 and 32.85 eggs/female) total fecundity of the Varamin and Rey populations were found at 20°C and 34°C, respectively. At the same time, these two populations had the highest intrinsic rate of increase (r) (0.0343 and 0.0349 d-1) at 30 and 27°C, respectively. Similarly, both Varamin and Rey populations had the highest finite rate of increase (λ) at 27°C (1.0349 and 1.0355 d-1, respectively). It was found that the geographical populations of S. cretica were different in terms of the life table parameters at the same temperatures, and this issue can affect the results of forecasting studies. Accordingly, it is suggested that in the major corn-growing areas, a comprehensive study should be performed on different pest populations to address their commonalities and differences for future managing programs.

Larval Migration Behaviour of Busseola fusca (Lepidoptera: Noctuidae) on Bt and Non-Bt Maize under Semi-Field and Field Conditions

Busseola fusca (Fuller) (Lepidoptera: Noctuidae) is a destructive pest of maize throughout the African continent. Bt maize is an effective control measure for this pest, however, selection pressure for resistance evolution is high. This necessitates the implementation of insect resistance management (IRM) strategies such as the high-dose/refuge strategy. This IRM strategy relies on the validity of several assumptions about the behaviour of pests during insect-hostplant interactions. In this study, the migration behaviour of B. fusca larvae was evaluated in a semi-field (greenhouse) and field setting. The effect of factors such as different Cry proteins, plant growth stage at infestation, and plant density on the rate and distance of larval migration were investigated over four and five week periods. Migration of the larvae were recorded by using both a leaf feeding damage rating scale and destructive sampling at the end of the trials. Results indicated that B. fusca larval migration success was significantly affected by plant growth stage and plant density-while limited larval migration was recorded in plots inoculated with larvae at a late growth stage (V10), higher plant density facilitated increased interplant migration. The results also suggest that B. fusca larvae do not migrate extensively (rarely further than two plants from the natal plant) and that larval mortality is high. Implications for IRM strategies are discussed.

Spatio-Temporal Interactions Between Maize Lepidopteran Stemborer Communities and Possible Implications From the Recent Invasion of Spodoptera frugiperda (Lepidoptera: Noctuidae) in Sub-Saharan Africa

Spatio-temporal dynamics of multi-species pest communities and the interactions between them influence the structure of pest complex that attack crops. In East and Southern Africa, cereal crops, especially maize, is attacked by a complex of lepidopteran stemborer species made up of Busseola fusca (Fuller) and Sesamia calamistis Hampson (Lepidoptera: Noctuidae), and Chilo partellus (Swinhoe) (Lepidoptera: Crambidae). There is inadequate information on the extent of single- and multi-species infestations by this pest complex, their current spatio-temporal variations, and the primary abiotic factors that influence these. Furthermore, the recent invasion of the fall armyworm, Spodoptera frugiperda J.E. Smith, in sub-Saharan Africa will likely influence this stemborer community structure. Sampling was conducted in maize fields to record stemborer species and larval numbers from infested plants, in 28 localities found in six agro-ecological zones (AEZs) of Kenya and parts of Tanzania, as well as in one locality in the mid-altitudes where the three stemborer species occurred together. Both single- and multi-species stemborer communities characterized infestation of maize at field and plant levels, but varied in proportions between the AEZs. Infestation patterns and larval densities varied between seasons at mid-locality stemborer communities followed a clustered distribution pattern. Temperature was the most significant abiotic factor influencing the composition of stemborer communities at all spatial scales. Rainfall was significant only at the local scale. Results are discussed in relation to current stemborer community structures in maize fields and what the likely potential implications are, in the light of climate change and the recent establishment of the fall armyworm in Africa.

Temperature effects on life history traits of two sympatric branchiopods from an ephemeral wetland

Temperature effects on organisms are of multiple scientific interests, such as for their life history performance and for the study of evolutionary strategies. We have cultured two sympatric branchiopod species from an ephemeral pond in northern Taiwan, Branchinella kugenumaensis and Eulimnadia braueriana, and compared their hatching rate, maturation time, sex ratio, growth of body length, survivorship, clutch size, net reproductive rate R₀, generation time T_G, and intrinsic rate of natural increase r in relation to temperature (15, 20, 25 and 30°C). We found that E. braueriana had a significantly higher temperature-dependent fecundity and intrinsic population growth pattern (R₀ and r). In contrast, B. kugenumaensis reproduced much slower than E. braueriana with much lower R₀ (90–100 folds less) and r (about 10 folds less) at 15, 20 and 25°C and with a double as long T_G at 20 and 25°C. In addition, E. braueriana increased its chance of hermaphroditic sexual reproductive mode at higher temperature because of a significantly delayed maturation of males from hermaphrodites. In contrast, B. kugenumaensis showed no significant change in reproductive mode with temperature. This is the first study indicating a significant differentiation in life history parameters of two sympatric branchiopods mediated by temperature.