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

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 (rm), 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

Predicting the impact of climate change on the potential distribution of the invasive tomato pinworm Phthorimaea absoluta (Meyrick) (Lepidoptera: Gelechiidae)

Abstract Phthorimaea absoluta (Meyrick) (= Tuta absoluta) (Lepidoptera: Gelechiidae), is the most damaging insect pest threatening the production of tomato and other solanaceous vegetables in many countries. In this study, we predicted the risk of establishment and number of generations for P. absoluta in the current and future climatic conditions under two Shared Socioeconomic Pathways (SSP2-4.5 and SSP5-8.5) of the years 2050 and 2070 using insect life cycle modelling (ILCYM) software. We used a temperature-dependent phenology model to project three risk indices viz., establishment risk index (ERI), generation index (GI), and activity index (AI) based on temperature data. The model projected large suitable areas for P. absoluta establishment in the Southern hemisphere under current and future climatic scenarios, compared to the Northern part. However, the risk of P. absoluta is expected to increase in Europe, USA, Southern Africa, and some parts of Asia in the future. Under current conditions, P. absoluta can complete between 6 and 16 generations per year in suitable areas. However, an increase in GI between 1 and 3 per year is projected for most parts of the world in the future, with an increase in AI between 1 and 4. Our results provide information on the risk of establishment of P. absoluta which could guide decision-makers to develop control strategies adapted for specific agro-ecological zones

Hot Water Disinfestation Treatment Does Not Affect Physical and Biochemical Properties of Export Quality Mango Fruit [<i>Mangifera indica</i> L.]

There are various postharvest treatments currently available in the market. Among these, heat-based treatments are very effective. Several hot water treatment (HWT) protocols at various temperature regimes and time durations have been developed for different mango cultivars and varieties. However, many concerns have been raised regarding the quality of fruits subjected to HWT, particularly on physical and biochemical properties. The purpose of this study was to generate empirical evidence on the effect of the HWT protocol currently recognized and accepted by the EU for Apple mango cultivar from Africa. We subjected mango to HWT at 46.1 °C for 68, 75, and 84 min and evaluated various physical and biochemical properties at 1, 3, 5, and 7 days post-treatment. Conventional methods of analysis were used to test acidity, antioxidants, minerals, nutrients, and physical properties of treated mangoes, and comparisons against untreated controls were made. We found no significant differences in pH, various acid content, total carotenoids, β-carotene content, vitamin A, aromatic volatiles, total phenolics, total antioxidant activity, various minerals, electrolytic leakage, crude protein, total carbohydrates, total sugars, crude fat, moisture content, dry matter, total soluble solids, firmness, or weight between treated and untreated mangoes. We conclude that HWT presents a viable alternative for postharvest treatment of export mangoes provided that quality attributes are maintained from preharvest, harvesting, transportation, treatment, and post-treatment handling

Hot Water Disinfestation Treatment Does Not Affect Physical and Biochemical Properties of Export Quality Mango Fruit [Mangifera indica L.]

There are various postharvest treatments currently available in the market. Among these, heat-based treatments are very effective. Several hot water treatment (HWT) protocols at various temperature regimes and time durations have been developed for different mango cultivars and varieties. However, many concerns have been raised regarding the quality of fruits subjected to HWT, particularly on physical and biochemical properties. The purpose of this study was to generate empirical evidence on the effect of the HWT protocol currently recognized and accepted by the EU for Apple mango cultivar from Africa. We subjected mango to HWT at 46.1 &deg;C for 68, 75, and 84 min and evaluated various physical and biochemical properties at 1, 3, 5, and 7 days post-treatment. Conventional methods of analysis were used to test acidity, antioxidants, minerals, nutrients, and physical properties of treated mangoes, and comparisons against untreated controls were made. We found no significant differences in pH, various acid content, total carotenoids, &beta;-carotene content, vitamin A, aromatic volatiles, total phenolics, total antioxidant activity, various minerals, electrolytic leakage, crude protein, total carbohydrates, total sugars, crude fat, moisture content, dry matter, total soluble solids, firmness, or weight between treated and untreated mangoes. We conclude that HWT presents a viable alternative for postharvest treatment of export mangoes provided that quality attributes are maintained from preharvest, harvesting, transportation, treatment, and post-treatment handling

A deadly encounter: Alien invasive Spodoptera frugiperda in Africa and indigenous natural enemy, Cotesia icipe (Hymenoptera, Braconidae)

The invasion and wide spread of Spodoptera frugiperda represent real impediments to food security and the livelihood of the millions of maize and sorghum farming communities in the sub-Saharan and Sahel regions of Africa. Current management efforts for the pest are focused on the use of synthetic pesticides, which are often economically unviable and are extremely hazardous to the environment. The use of biological control offers a more economically and environmentally safer alternative. In this study, the performance of the recently described parasitoid, Cotesia icipe, against the pest was elucidated. We assessed the host stage acceptability by and suitability for C. icipe, as well as its ovigenic status. Furthermore, the habitat suitability for the parasitoid in the present and future climatic conditions was established using Maximum Entropy (MaxEnt) algorithm and the Genetic Algorithm for Rule-set Prediction (GARP). Cotesia icipe differentially accepted the immature stages of the pest. The female acceptance of 1 st and 2 nd instar larvae for oviposition was significantly higher with more than 60% parasitism. No oviposition on the egg, 5 th and 6 th larval instars, and pupal stages was observed. Percentage of cocoons formed, and the number of emerged wasps also varied among the larval stages. At initial parasitism, parasitoid progenies, time to cocoon formation and overall developmental time were significantly affected by the larval stage. Egg-load varied significantly with wasp age, with six-day-old wasps having the highest number of mature eggs. Ovigeny index of C. icipe was 0.53. Based on the models, there is collinearity in the ecological niche of the parasitoid and the pest under current and future climate scenarios. Eastern, Central and parts of coastal areas of western Africa are highly suitable for the establishment of the parasitoid. The geographic distribution of the parasitoid would remain similar under future climatic conditions. In light of the findings of this study, we discuss the prospects for augmentative and classical biological control of S. frugiperda with C. icipe in Africa

The South America tomato leafminer, Tuta absoluta (Lepidoptera: Gelechiidae), spreads its wings in Eastern Africa: distribution and socioeconomic impacts

Following the arrival of Tuta absoluta Meyrick in the eastern African subregion in 2012, several studies have shown numerous ecological aspects of its invasion. We investigated the impact of T. absoluta on people's livelihoods across four counties of Kenya. Here, 200 farmers in the country were interviewed in person using semistructured questionnaires. In addition to livelihood surveys, T. absoluta distribution was mapped between 2016 and 2018 to determine its current distribution across four countries (Kenya, Sudan, Tanzania, and Uganda) in the subregion. Albeit a recent invader, T. absoluta is abundant and distributed throughout the subregion and is viewed as the worst invasive alien species of agriculturally sustainable livelihoods by tomato farmers. The arrival of T. absoluta in the subregion has resulted in livelihood losses and increased both the cost of tomato production and frequency of pesticide application. We recommend the implementation of biological control along, with other control measures in an integrated approach, against T. absoluta in the subregion, where its impact on sustainable livelihoods is serious and long-term control strategies are required to curb its detrimental effects