Yves Dumont

Elaeidobius kamerunicus completes its life cycle on male inflorescences while ensuring pollen transfer to female inflorescences. Over the past decades, oil palm breeding has prioritized yield potential over male inflorescence production. In young plantations, scare male inflorescences may result in insufficient pollen and breeding sites for E. kamerunicus , reducing or eliminating local populations. Consequently, reduced pollination lowers fruit set and yield. Our study assessed weevil emergence phenology and potential from 74 post-anthesis male inflorescences of two cultivars: 31 from a super-male and 43 from a high-yielding experimental cultivar. Male spikelet morphology was compared using field and laboratory data collected in North Sumatra in Indonesia (2020-2022). Super-male palms had more spikelets (283 vs.174), greater total spikelet length (39 vs. 27 m) and higher E. kamerunicus emergence (17,500 vs. 13,100). The kinetic of emergence reveals that E. kamerunicus females emerged in a large number during 10 days and earlier than males which emerged during a longer period of time (18 days), indicative of protogyny in adult emergence. The predicted emergence kinetics indicate that E. kamerunicus from Experimental cultivar emerged earlier (1-2 days) than E. kamerunicus from Supermale and it also shows a difference in the timing of emergence between the two sexes. Thus, sex and cultivar jointly influence the emergence dynamics of E. kamerunicus . There was good evidence that the total length of the spikelets in an inflorescence positively influences the number of E. kamerunicus emergence events. We will discuss our results from the point of view of pollination.

During the 1980’s, Elaeidobius kamerunicus , one of the oil palm pollinator species in Africa, was successfully introduced in Indonesia from Cameroon to improve oil palm production and reduce assisted pollination. It is now well known that E. kamerunicus completes its entire life cycle on the anthesis of the male inflorescences. However, for a long time, oil palm breeding programs have favoured the development of female inflorescences for production purposes, to the detriment of male inflorescences. The objective of our study was to explore the interactions between the weevil population, at immature stages, and male inflorescences, produced by two different cultivars (a super-male (SM) cultivar and a highly female and productive experimental cultivar (EXP) of five years old) during anthesis and post-anthesis stages. Morphological characteristics of spikelets of inflorescences were also studied and compared. We analysed field and laboratory data, collected in North Sumatra (Indonesia) from April to June 2019. The mean number of spikelets is lower in EXP palms (126±16) than in SM palms (213±15). There are more abnormal spikelets in SM palms (126±77 and 100±73 for SM-SD and SM-DD cultivars, respectively), than in EXP palms (33±23). However, all these differences do not affect either male inflorescences number of flowers or their carrying capacity that contributes to E. kamerunicus development. The number of male flowers per inflorescences is almost the same for both materials, and about 10% of flowers were occupied by E. kamerunicus immature stages. Despite noticeable morphological differences, no major differences were found between male inflorescences of EXP and SM cultivars. We will discuss our results from pollination point of view.

The sterile insect technique (SIT) is a biological control method aimed at reducing or eliminating populations of pests and disease vectors. This technique involves releasing sterilised insects which, by mating with wild individuals, will reduce the target population. In this study, spatial aspects are incorporated through an explicit metapopulation model, in which both wild and sterile insects disperse across multiple patches. We derive a general sufficient condition ensuring elimination of the wild population in all patches through SIT. When a strong Allee effect is naturally present in each patch, the release programme can be terminated after a finite time, and an upper bound on the required release duration is provided. We then study an optimisation problem aimed at minimising the daily number of sterile insects released to ensure population elimination, under the constraint that the releases occur only in a prescribed subset of patches. For illustrative purposes, we explore through numerical simulations different dispersal network configurations. We also consider additional control by mass trapping (MT), which can affect the sterile insects entering trapped areas. The main contribution of this work is to enable the identification of the best spatial strategies for releasing sterile insects under practical constraints, in order to achieve population elimination.

Yield improvement is a main issue in the oil palm industry. Several ways to achieve this goal are possible, like, for instance, improving fruit set. Here we explore a planting strategy to increase two major factors influencing pollination; i.e. (1) the number of individuals of its main pollinator, Elaeidobius kamerunicus Faust , and (2) pollen availability, by mixing oil palm planting material, usually highly feminine, with a new oil palm material, the “super-male” (SM) planting material, with a high ratio of male inflorescences. We design and study a field trial comprising extremely feminine planting material mixed with different SM densities. Using Mark-Release-Recapture experiments we estimate the average dispersal of the pollinators over three different periods of the year, from 2017 till 2022. Second, using phenological data recorded over the same period, we studied the impact of the SM planting density on the population size of the pollinators. Finally, we assess the impact over time of different SM planting densities on the fruit set, the fruit-to-bunch, and the number of trapped wild pollinators. The combination of SM material with a highly feminine planting material provides very promising results in terms of fruit set, linked with increased pollinator population and pollen availability, demonstrating its potential for application in oil palm plantations.

Anthropisation and excessive hunting in tropical forests threaten biodiversity, ecosystem maintenance, and human food security. In this article, we focus on the issue of coexistence between humans and wildlife in an anthropised environment. Assuming that humans move daily between their residential area and the surrounding forest to hunt, we study a resource‐consumer model with consumer migration. A comprehensive analysis of the system is carried out using classical theory and monotone systems theory. We show that the possibilities for long‐term coexistence between human populations and wildlife populations are determined by hunting rate thresholds. Depending on the level of anthropisation and the hunting rate, the system may converge towards a limit cycle or a co‐existence equilibrium. However, the conditions for coexistence become more difficult as anthropisation increases. Numerical simulations are provided to illustrate the theoretical results.

The Sterile Insect Technique (SIT) is a biological control method used to reduce or eliminate pest populations or disease vectors. This technique involves releasing sterilized insects that, upon mating with the wild population, produce no offspring, leading to a decline or eventual eradication of the target species. We incorporate a spatial dimension by modeling the pest/vector population as being distributed across multiple patches, with both wild and released sterile insects migrating between these patches at predetermined rates. We mainly focus on a two-patch system. This study has two primary objectives: first, to derive sufficient conditions for achieving the elimination of the wild population through SIT, whether releases occur in one patch or in both patches. In particular, we provide an estimate of the minimal release rates to reach elimination thanks to the diffusion rates between patches. This is the first time that such a result is given in a general manner. Second, we study an optimal SIT control strategy, where we minimize the total amount of sterile insects to release, and show that, within one patch, it can successfully reduce the wild population in that patch to a desired level within a finite time frame, provided that the migration rates between patches are sufficiently low. Numerical simulations are employed to illustrate these results and further analyze the outcomes.

Anthropisation and excessive hunting in tropical forests threaten biodiversity, ecosystem maintenance and human food security. In this article, we focus on the issue of coexistence between humans and wildlife in an anthropised environment. Assuming that the human population moves between its residential area and the surrounding forest to hunt, we study a resource-consumer model with consumer migration. A comprehensive analysis of the system is carried out using classical theory and monotone systems theory. We show that the possibilities for long-term coexistence between human populations and wildlife populations are determined by hunting rate thresholds. Depending on the level of anthropisation and the hunting rate, the system may converge towards a limit cycle or a co-existence equilibrium. However, the conditions for coexistence become more difficult as anthropisation increases. Numerical simulations are provided to illustrate the theoretical results.

The Sterile Insect Technique (SIT) is a biological control method used to reduce or eliminate pest populations or disease vectors. This technique involves releasing sterilized insects that, upon mating with the wild population, produce no offspring, leading to a decline or eventual eradication of the target species. We incorporate a spatial dimension by modeling the pest/vector population as being distributed across multiple patches, with both wild and released sterile insects migrating between these patches at predetermined rates. We mainly focus on a two-patch system. This study has two primary objectives: first, to derive sufficient conditions for achieving the elimination of the wild population through SIT, whether releases occur in one patch or in both patches. In particular, we provide an estimate of the minimal release rates to reach elimination thanks to the diffusion rates between patches. This is the first time that such a result is given in a general manner. Second, we study an optimal SIT control strategy, where we minimize the total amount of sterile insects to release, and show that, within one patch, it can successfully reduce the wild population in that patch to a desired level within a finite time frame, provided that the migration rates between patches are sufficiently low. Numerical simulations are employed to illustrate these results and further analyze the outcomes.