Modelling Allee effects in a transgenic mosquito population during range expansion

Mathematical modeling of the performance of wild and transgenic mosquitoes in malaria transmission

A mathematical model that simulates malaria transmission under the influence of transgenic mosquitoes refractory to malaria is presented in this paper. The zygosity of transgenic mosquitoes is taken into account and, consequently, the total population of mosquitoes is comprised of wild type and heterozygous and homozygous transgenic mosquitoes. These three mosquito varieties interact by mating and competition, and the genetic characteristics of their resulting offspring are in accordance with Mendelian genetics or the mutagenic chain reaction (MCR) technique. Although the incorporation of transgenic mosquitoes into the ecosystem reduces the incidence of malaria, the model also takes into account the importance of completing treatment in individuals with confirmed infection and the imminent risk of increased environmental temperature.

Biological Strategies of Invasive Bark Beetles and Borers Species

Simple Summary

Biological invasions are one of the most critical problems today. Invaders have been damaging tree- and shrub-dominated ecosystems. Among these harmful species, a notable role belongs to bark beetles and borers. Extensive phytosanitary measures are needed to prevent their penetration into new regions. However, the lists of quarantine pests should be reasonably brief for more effective prevention of invasion of potentially harmful insects. Our goal is to reveal the set of biological traits of invasive bark beetles and borers that are currently known. We identified four invasion strategies. Inbred, the first one is characterized by inbreeding, parthenogenesis, polyvoltinism, xylomycetophagy, flightless males, polyphagy, to less extent by association with pathogenic fungi. For the second, polyphagous, typical traits are polyphagy, feeding on wood, high fecundity, distance sex pheromones presence, development for one year or more. The third strategy, intermediate, possesses such features as mono- or olygophagy, feeding on inner-bark, short (one year or less) life cycle. Aggressive, the last one includes monophagous species using aggregation pheromones, associated pathogens, short life cycle, and consuming inner-bark. The main traits contributing to significant damage are high fecundity, polyvoltinism, symbiotic plant pathogens, long-range or aggregation pheromones.

Abstract

The present study attempts to identify the biological characteristics of invasive (high-impact in the secondary area) bark beetles and borers species, contributing to their success in an invaded area. We selected 42 species based on the CABI website data on invasive species and information on the most studied regional faunas. Four groups of species with different invasion strategies were identified based on the cluster and factor analysis. The first one (inbred strategy) is characterized by flightless males, xylomycetophagy, low fecundity (~50 eggs), inbreeding, polyvoltinism, and polyphagy. Species with an aggressive strategy are poly- or monovoltine, feeds on a limited number of hosts, larval feeding on the inner bark, are often associated with phytopathogens, and produce aggregation pheromones. Representatives of the polyphagous strategy have a wide range of hosts, high fecundity (~150 eggs), larval feeding on wood, and their life cycle is at least a year long. For the intermediate strategy, the typical life cycle is from a year or less, medium fecundity, feed on inner bark tissues, mono- or oligophagy. Comparison with low-impact alien species showed that the most significant traits from the viewpoint of the potential danger of native plant species are high fecundity, polyvoltinism, presence of symbiotic plant pathogens, long-range or aggregation pheromones.

Population Dynamics of Underdominance Gene Drive Systems in Continuous Space

Underdominance systems can quickly spread through a population, but only when introduced in considerable numbers. This promises a gene drive mechanism that is less invasive than homing drives, potentially enabling new approaches in the fight against vector-borne diseases. If regional confinement can indeed be achieved, the decision-making process for a release would likely be much simpler compared to other, more invasive types of drives. The capacity of underdominance gene drive systems to spread in a target population without invading other populations is typically assessed via network models of panmictic demes linked by migration. However, it remains less clear how such systems would behave in more realistic population models where organisms move over a continuous landscape. Here, we use individual-based simulations to study the dynamics of several proposed underdominance systems in continuous-space. We find that all these systems can fail to persist in such environments, even after an initially successful establishment in the release area, confirming previous theoretical results from diffusion theory. At the same time, we find that a two-locus two-toxin-antidote system can invade connected demes through a narrow migration corridor. This suggests that the parameter space where underdominance systems can establish and persist in a release area while at the same time remaining confined to that area could be quite limited, depending on how a population is spatially structured. Overall, these results indicate that realistic spatial context must be considered when assessing strategies for the deployment of underdominance drives.