Temperature-dependent development and survival of immature stages of the coffee berry borer Hypothenemus hampei (Coleoptera: Curculionidae)

Evaluation of suitable reference genes for expression profile analyses of target genes in the coffee berry borer, Hypothenemus hampei (Ferrari) (Coleoptera: Curculionidae)

The coffee berry borer, Hypothenemus hampei (Ferrari) (Coleoptera: Curculionidae), is a major destructive insect pest of coffee, which impacts the coffee crops negatively. As a draft genome has been completed for this insect, most molecular studies on gene transcriptional levels under different experimental conditions will be conducted using real-time reverse-transcription quantitative polymerase chain reactions (RT-qPCR). However, the lack of suitable internal reference genes will affect the accuracy of RT-qPCR results. In this study, the expression stability of nine candidate reference genes was evaluated under different developmental stages, temperature stress, and Beauveria bassiana infection. Data analyses were completed by four commonly used programs, BestKeeper, NormFinder, geNorm, and RefFinder. The result showed that RPL3 and EF1α combination were recommended as the most stable reference genes for developmental stages. EF1α and RPS3a combination were the top two stable reference genes for B. bassiana infection. RPS3a and RPL3 combination performed as the optimal reference genes both in temperature stress and all samples. Our results should provide a good foundation for the expression profile analyses of target genes in the future, especially for molecular studies on insect genetic development, temperature adaptability, and immune mechanism to entomogenous fungi in H. hampei.

Temperature-Dependent Biology and Population Performances of the Coffee Berry Borer Hypothenemus hampei (Ferrari) (Coleoptera: Curculionidae: Scolytinae) on Artificial Diet

At different observation intervals of 1, 5, and 10 days during a trial period of 30 days, the mortality rates of Hypothenemus hampei were 100, 95, and 55%, and the fecundity rates were 0.55, 8.45, and 19.35 eggs/female, respectively. At temperatures of 18, 21, 24, and 27 °C, the development time of the immature stage of H. hampei was significantly shortened with increasing temperature. Furthermore, the lower developmental threshold (T₀) and thermal summation (K) of the immature stage were 8.91 °C and 485.44 degree-days, respectively. The greatest longevity of female and male adults reached 115.77 and 26.50 days, respectively, at 18 °C. The highest fecundity was 29.00 eggs/female at 24 °C. The population parameters of H. hampei were analyzed on the basis of the age-stage, two-sex life table theory. According to the data, the parameters were significantly affected by temperature. The highest net reproductive rate (R₀) was 13.32 eggs/individual at 24 °C. The highest intrinsic rate of increase (r) and finite rate of increase (λ) were calculated as 0.0401 and 1.0409 day^-1, respectively, at a temperature of 27 °C. The shortest mean generation time (T) was 51.34 days at 27 °C. Overall, we provide a discussion on comprehensive biological information regarding H. hampei, thus providing basic knowledge for further research on this pest.

Integrating temperature-dependent development and reproduction models for predicting population growth of the coffee berry borer, Hypothenemus hampei Ferrari

The coffee berry borer, Hypothenemus hampei Ferrari (Coleoptera: Curculionidae, Scolytinae), is the most devastating insect pest of coffee worldwide. It feeds on the beans inside the berries leading to significant crop losses and unmarketable products. This study aims to model the impact of temperature on H. hampei fecundity and population growth parameters, as a contribution to the prediction of infestation risk. The fecundity was assessed on fresh coffee beans at six constant temperatures in the range 15-30°C, with RH 80 ± 5% and photoperiod 12:12 L:D. Nonlinear models were fitted to the relationship between fecundity and temperature using the ILCYM software. The best fecundity model was combined to development models obtained for immature stages in a previous study in order to simulate life table parameters at different constant temperatures. Females of H. hampei successfully oviposited in the temperature range 15-30°C, with the highest fecundity observed at 23°C (106.1 offspring per female). Polynomial function 8 model was the best fitted to the relationship between fecundity and temperature. With this model, the highest fecundity was estimated at 23°C, with 110 eggs per female. The simulated net reproductive rate (R₀) was maximal at 24°C, with 50.08 daughters per female, while the intrinsic rate of increase (r_m) was the highest at 26°C, with a value of 0.069. Our results will help understand H. hampei population dynamics and develop an ecologically sound management strategy based on a better assessment of infestation risk.

Effects of temperature on the fitness of the alfalfa weevil (Hypera postica)

BACKGROUND

Temperature directly influences the survival, development and reproduction of insects and limits their biological activity. The alfalfa weevil (Hypera postica Gyllenhal) is a destructive pest of alfalfa crops in Spain and in most of the alfalfa production countries. The knowledge of how temperature affects the fitness of this pest can be used to predict its activity in current or forecasted environmental conditions and to develop more accurate control strategies.

RESULTS

We evaluated the fitness of alfalfa weevil at eight constant temperatures (8-36 °C) at 4 °C intervals by using life tables and models for the description of temperature-dependent development rates. We found that most of the parameters we studied were temperature dependent. Development was observed at all temperatures. However, postembryonic survival was optimal at 16 °C but very low at 36 °C. Adults did not reproduce at 8, 32 or 36 °C. The highest fecundity and net reproductive rate were observed at 20 °C, but the highest intrinsic rate of increase occurred at 24 °C. We predicted the phenology of the pest based on the heat needed for development, the cumulative degree days from the beginning of October to the end of May, and the day length in the study region.

CONCLUSION

Our prediction was validated using field data reporting the first occurrence of larval instars and adults, revealing that no more than two generations are possible within an annual cycle. In a hypothetical case where average monthly temperatures increase by 1-2 °C, the number of generations would not change. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Estimating the Demographic Parameters of Tuta absoluta (Lepidoptera: Gelechiidae) Using Temperature-Dependent Development Models and Their Validation under Fluctuating Temperature

Simple Summary

Tuta absoluta is an invasive insect pest that has spread widely and established itself in many countries since its first detection in Spain in 2006. The devastating moth originates in South America and attacks tomato and other solanaceous vegetables, leading to huge losses in yield and potential income particularly for small-scale farmers who often lack the resources and knowledge to manage the pest. In most cases, farmers have resorted to the indiscriminate application of broad-spectrum synthetic pesticides, which in most cases are not registered and are often used at high doses. This has resulted in the pest developing resistance to most major classes of pesticides. In addition, the non-selective use of toxic pesticides has resulted in negative effects on the health of users, consumers, and non-target organisms such as pollinators and natural enemies of insect pests. Various tactics aimed at controlling T. absoluta have been developed and are at different stages of adoption by farmers. To ensure that they are effective, sustainable, and friendly to both users and the environment, there is a need for a comprehensive understanding of the pest’s biology and ecology. To this effect, the present study developed models to predict intricate details of the pest’s development, survival, and reproduction using data generated in laboratory studies. Among other important findings, the study reports that temperatures between 20–25 °C are ideal for the development, survival, reproduction, and increase in the population of T. absoluta. These findings are vital in developing strategies in managing the pest, especially in light of global climate change.

Abstract

The tomato leafminer, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) is an invasive pest that devastates the production of tomatoes and other solanaceous vegetables. Since its trans-Atlantic invasion in 2006, T. absoluta has spread and established in many countries across the Afro-Eurasian Supercontinent, causing huge yield losses. This study aimed to determine the relationship between temperature and the life history traits of T. absoluta and provide the thermal thresholds for development using life cycle modelling. Linear and non-linear models were fitted to life table data collected at five constant temperatures of 15, 20, 25, 30, and 35 °C, with Relative Humidity 70 ± 5% and photoperiod 12L:12D. Another experiment was conducted at fluctuating temperatures to validate the laboratory results. Tuta absoluta completed its life cycle at temperatures between 15 and 35 °C. The development time ranged between 4.0–11 days, 6.3–16.0 days, and 5.4–20.7 days for egg, larva, and pupa, respectively. The lowest thermal threshold was estimated at 8.10, 7.83, and 11.62 °C, respectively for egg, larva, and pupa. While the optimum temperature for T. absoluta immature stages survival and female fecundity were predicted at a temperature range of 21–23 °C. The intrinsic rate of increase (r_m), gross reproductive (GRR), and net reproductive (Ro) rates were significantly higher at temperatures between 20–25 °C. The model validation outcome showed similarities between observed and simulated values for development time, mortality rate, and life table parameters, attesting to the quality of the phenology model. Our results will help in predicting the effect of climate warming on the distribution and population dynamics of T. absoluta. Furthermore, the results could be used to develop management strategies adapted to different agroecological zones.

Determination of temperature thresholds for the parasitoid Diachasmimorpha longicaudata (Hymenoptera: Braconidae), using life cycle simulation modeling: Implications for effective field releases in classical biological control of fruit flies

The braconid parasitoid Diachasmimorpha longicaudata (Ashmead) (Hymenoptera: Braconidae) is one of the most important natural enemies in classical biological control programs against tephritid fruit flies worldwide. In light of the spread of the invasive fruit fly species, Bactrocera dorsalis in Africa and beyond, there is a need to implement classical biological control. The current study aimed to determine temperature thresholds for D. longicaudata reared on B. dorsalis, using life cycle simulation modeling to guide informed parasitoid releases in Africa. Simulated parameters included thermal requirements, population growth parameters at different temperature requirements, suitable areas for the establishment, and the number of generations per year under projected climatic conditions. The lower thermal threshold for the development was estimated at 10.0°C, with a thermal constant (k) of 333.3-degree days, while the maximum temperature threshold was estimated at 33.69°C. Fecundity was highest at 25°C, with 177.3 eggs per female. Temperature significantly affected the population growth parameters of D. longicaudata, and the maximum value of the intrinsic rate of increase (rm) was 0.145 at 27°C. Results indicate that D. longicaudata could successfully establish in tropical and sub-tropical regions under current and future climatic conditions. However, a slight change in the suitable areas is expected by the year 2050 due to a slight and gradual rise in temperature. Our findings provide important information for further release of this parasitoid in Africa as well as designing pest management strategies to limit the spread and reduce the impact of fruit flies sustainably.

Temperature-dependent development models describing the effects of temperature on the development of Spodoptera eridania

BACKGROUND

The southern armyworm, Spodoptera eridania, is a polyphagous species native to the American tropics that recently invaded Africa. Knowledge of the impact of temperature on its development and survival is important to understand the risks of this species spreading to other regions and to develop phenological models for pest management. This study evaluated the effects of temperature on the development and survival of S. eridania and selected mathematical models to simulate its development.

RESULTS

The southern armyworm completed its development between 15 and 32 °C, but eggs did not hatch at 34 °C. Lower survival and higher rates of deformities in adults were recorded at 15 and 32 °C. Among the ten mathematical models evaluated, Briere-2, Lactin-2 and Shi were considered suitable for describing the temperature-dependent development rate of S. eridania. The lower thermal threshold estimated by these models for the egg to adult life cycle ranged from 10.8 to 12.1 °C, whereas the upper threshold ranged between 33.9 and 35.0 °C.

CONCLUSIONS

The southern armyworm can develop within a wide range of temperatures, which partially explains its wide distribution in regions with different climatic conditions, and demonstrates its potential to occur in regions outside its native range. Our findings can be employed in the development of management strategies using the selected models to predict the occurrence of S. eridania in the field and determine the most effective times to implement control measures.