Thomas Dubois

Climate change is expected to heighten the risk of epidemics and outbreaks of coffee leaf rust (CLR), caused by the obligate parasite Hemileia vastatrix, as reported in the literature. While knowledge is available on rising temperatures’ effects on CLR epidemiological processes, fewer studies have explored combined temperature and atmospheric carbon dioxide (CO ₂ ) impacts, with contrasting findings on CLR incidence and severity. CLR epidemics are multifactorial, and controlled-condition experiments targeting individual components help anticipate pathogen behavior under future climates. Urediniospore germination, a time-efficient indicator, enables exploration of pathogen responses across diverse temperature–CO ₂ combinations, providing insights into CLR epidemiological shifts. We investigated H. vastatrix urediniospore germination under varying combinations of temperature and atmospheric CO ₂ in controlled conditions (in phytotrons), testing 30 combinations of temperatures (16 to 32°C) and atmospheric CO ₂ concentrations (181 to 707 ppm). The fitted generalized linear model with a binomial distribution within an augmented design framework to our data was robust (pseudo-R ² = 0.78) and revealed that germination probability followed a quadratic pattern as a function of varying atmospheric CO ₂ , with optima dependent on both CO ₂ and temperature. Urediniospore germination probabilities are optimized (p _max ) below the current CO ₂ (424 ppm) at 24°C (p _max = 0.45) and 28°C (p _max = 0.43) and above 424 ppm at 16°C (p _max = 0.34) and 32°C (p _max = 0.35). This indicates that elevated CO ₂ can partly compensate for less suitable temperatures while reducing germination within the current optimal range. Overall, our results highlight a trade-off in which rising CO ₂ reshapes, rather than uniformly increases, infection opportunities under climate change, providing new data for future risk models.

The spotted stem borer ( Chilo partellus ) is one of the most destructive pests of maize in sub‐Saharan Africa, causing substantial yield losses and threatening food security among smallholder farming communities. This study investigated the long‐term relationships between climatic variability and C. partellus incidence across contrasting organic and conventional farming systems in two agroecological zones. Biweekly monitoring observations of C. partellus incidence were summarized quarterly for temporal analyses across four long‐term farming systems at Chuka and Thika: conventional high‐, organic high‐, conventional low‐, and organic low‐input. The resulting analytical series represented 32 and 28 quarterly positions at Chuka and Thika, respectively. Climatic variables (temperature, rainfall, and relative humidity) were obtained from on‐site weather stations. Spearman’s rank correlation, cross‐correlation, ARIMA/SARIMA time‐series models with exogenous climatic predictors (ARIMAX/SARIMAX), and Bayesian generalized linear mixed models were used to evaluate climatic associations and farming systems effects. Temperature emerged as the climatic variable most consistently associated with C. partellus incidence, showing significant negative relationships across all farming systems at Chuka and within the organic farming systems at Thika, whereas rainfall and relative humidity exhibited comparatively weak associations. Cross‐correlation analyses indicated predominantly contemporaneous and short lag associations (0–2 quarters) between climatic variables and pest incidence. Time‐series models were evaluated using descriptive measures of in‐sample agreement between observed and fitted values. Across farming systems, R ² values ranged from 0.039 to 0.650, indicating substantial variation in the degree to which the fitted models represented the observed temporal patterns. These measures describe in‐sample model fit and should not be interpreted as evidence of out‐of‐sample predictive or forecasting performance. Bayesian analyses further indicated that C. partellus incidence was higher in the organic than in the conventional high‐input systems after accounting for climatic variability, whereas the 95% credible intervals for farming system effects in the low‐input systems overlapped zero. Overall, these findings suggest that climatic variability and farming system management are associated with long‐term variation in C. partellus incidence. The findings may inform the development of climate‐informed pest‐monitoring and integrated pest management strategies, while independently validated models would be required before application for pest forecasting under sustainable maize production in East Africa.

Multi-floral foraging sources for honey bee (Apis mellifera L.) have been threatened by landscape changes and unsustainable farming practices. In East Africa, the biodiversity of forage resources that could support honey bees, especially in agricultural lands, remains least explored. This study investigated pollen diversity for honey bees in Yatta and Masinga Sub-counties in Machakos County, Kenya. Honey bee hives were installed on eight pumpkin (Cucurbita maxima Duchesne ex Lam) farms (one hive per farm) in two varying landscape vegetation classes (low and medium) based on normalized difference vegetation index (NDVI). Pollen traps were installed at the hive entrance and pollen pellets were retrieved fortnightly for subsequent identification. Approximately 115 pollen types were identified. The pollen pellets were associated with 63 plant families and 109 plant families in low and medium NDVI classes, respectively. The predominant source of pollen for honey bees in low NDVI class included the plant families Poaceae (5,526 pellets), Asteraceae (3,176 pellets), Combretaceae (1,327 pellets), Acanthaceae (1,122 pellets), Amaranthaceae (960 pellets), Boraginaceae (951 pellets), Typhaceae (889 pellets), Guaduelleae (809 pellets) and Loranthaceae (588 pellets). In medium NDVI, most pollen was sourced from plant family Asteraceae (3,605 pellets), Malvaceae (1,572 pellets), Poaceae (1,538 pellets), Combretaceae (1,468 pellets), Salvadoraceae (1,354 pellets), Solanaceae (1,011 pellets), Asphodelaceae (885 pellets), Fabaceae (882 pellets), Euphorbiaceae (685 pellets) and Myrtaceae (546 pellets). The diversity of pollen types varied between the NDVI classes and across months. Although honey bees sourced diverse pollen required for the dietary balance of the colony, there was variability across landscape types and months.

Vegetable production is vital to smallholder farmers, who often struggle to overcome pests, diseases, and extreme weather. Agroecological cropping systems offer sustainable solutions to these issues but their adoption rates in Tanzania remain low. This study examines the factors influencing smallholder farmers’ adoption of selected agroecological cropping systems for vegetable production in Tanzania, which remains underexplored. Using a multistage sampling technique, cross-sectional data were gathered from 525 crucifer and traditional African vegetable farming households within the Arusha and Kilimanjaro regions. Multivariate probit regression analysis, which accounts for the simultaneous adoption of multiple systems, revealed several significant variables influencing adoption. The number of training sessions attended and access to market information positively influenced adoption (p < 0.01), while gross income from vegetable production also had a positive influence (p < 0.05). Conversely, the age of the household head and the region where the farm was located showed negative effects on adoption (p < 0.05). These findings highlight the need for targeted extension services and training sessions focusing on the benefits, methods, and management techniques of agroecological cropping systems. Gender-sensitive policies and interventions should also be developed to address the factors influencing the adoption of agroecological cropping systems.

Avocado is a pollinator-dependent crop rich in fiber, monounsaturated oils, vitamins, and minerals, which is seeing an increase in global demand. While some studies have shown that insect pollination improves avocado fruit set, the effects of pollinators on fruit quality and the nutritional profile remain unclear. Furthermore, it remains untested whether a potential pollination deficit can be compensated by the supplementation of farms with extra pollinators. We quantified the contribution of insect pollination on fruit and seed weight, and oil, protein, carbohydrate, and phytochemical (flavonoid and phenolics) contents, and assessed if the supplementation of pollinators on farms can improve fruit parameters. The experiment was conducted in 36 smallholder avocado farms of which 18 farms were supplemented with two Apis mellifera bee hives, while 18 were used as controls. Four manipulative pollination treatments were conducted: hand, open, self- and wind pollination. We observed that avocado fruit weight was significantly higher (213.7 g) for insect pollinated flowers than in case of wind- (107.8 g) or self-pollination (95.1 g).Insect pollination resulted in heavier seeds (29.5 g) as well as higher oil contents, clearly showing that insect pollination was required to reach a high seed yield and quantity of oil. Honey bee supplementation on farms enhanced the avocado fruit weight by 18%, and increased avocado oil content by 3.6%. As the marketability of avocado directly depends on fruit size and oil content, a sustainable management of bee communities may be of key importance for the long-term profitability of avocado agriculture.

The greater pumpkin fly Dacus bivittatus (Bigot) is a fruit fly indigenous to Africa, which causes extensive damage to Cucurbitaceae. To control this pest, farmers rely on synthetic chemicals, often organophosphates, which have negative effects on human health and the environment. However, the sustainable management of D. bivittatus may be obtained through integrated pest management (IPM) practices, with the use of biopesticides as a key component. In this study, the effect of nine isolates of the entomopathogenic fungus Metarhizium anisopliae (Metschnikoff) Sorokin (ICIPE 18, ICIPE 20, ICIPE 30, ICIPE 48, ICIPE 62, ICIPE 69, ICIPE 84, ICIPE 91 and ICIPE 94) was directly evaluated on adult D. bivittatus mortality. Adult flies were allowed to walk for 5 min on 0.3 g of dry conidia of each isolate and monitored daily for 10 days. We also evaluated the effect of sand inoculated with M. anisopliae on larval and pupal mortality and adult eclosion and mortality in three replicated experiments. Larvae were exposed to the same isolates at a concentration of 1 × 10⁷ conidia/mL in sterile sand, and adult eclosion and mortality were monitored for 15 days. The median lethal time (LT₅₀) of adults after direct exposure was shortest for ICIPE 18, ICIPE 20, ICIPE 30 and ICIPE 69 (3.11–3.52 days). In infested sand, larval mortality was highest for ICIPE 18 and ICIPE 20 (≥42.50%), while pupal mortality was highest for ICIPE 30 (≥41.25%). The lowest eclosion was observed for ICIPE 18, ICIPE 20, ICIPE 30 and ICIPE 69 (≤40.00%). The LT₅₀ of adults eclosed from infested sand was shortest for ICIPE 18, ICIPE 20 and ICIPE 30 (4.48–6.95 days). ICIPE 18, ICIPE 20, ICIPE 30 and ICIPE 69 are, therefore, potential isolates for subsequent field testing on D. bivittatus populations.

In the laboratory, the pathogenicity of thirteen isolates of Metarhizium anisopliae (Metschnikoff) Sorokin and two isolates of Beauveria bassiana (Balsamo) Vuillemin against the melon fly Zeugodacus cucurbitae (Coquillett) were assessed by exposing adults to 0.3 g of dry conidia (~3 × 10⁹ conidia) of each isolate for 5 min and monitoring mortality for up to 5 days. Compatibility with a male pheromone, cuelure, (4-(p-acetoxyphenyl)-2-butanone), was determined by testing conidial germination and germ tube growth of the most promising isolate, M. anisopliae ICIPE 69, in the presence of cuelure at different temperatures. For horizontal transmission, the flies were separated by sex, separately exposed to M. anisopliae ICIPE 69, and subsequently mixed with non-exposed flies from the other sex. The most pathogenic isolates were M. anisopliae ICIPE 69, 18, and 30, causing mortalities of 94, 87, and 81%, with 5 days post-exposure, respectively. Metarhizium anisopliae ICIPE 69 caused the highest pupal mortality of 74%, with 15 days post-exposure. Horizontal transmission of M. anisopliae ICIPE 69 among male and female Z. cucurbitae was confirmed by 59 and 67% mortality after exposure to infected donor males and females, respectively. Metarhizium anisopliae ICIPE 69 affected the oviposition, but not hatchability, of infected Z. cucurbitae females. Metarhizium anisopliae ICIPE 69 is, therefore, a potential isolate for biopesticide development for Z. cucurbitae management in cucurbit production systems.