Invasive species can strongly affect biotic interactions in ecosystems, interacting both directly and indirectly with local species. In European tomato greenhouses, the invasive alien pest Tuta absoluta may impact the population dynamics of other pests like whiteflies. Besides inducing damages to the host plant and competing for resources with local pests, this alien species may exert a predator‐mediated interaction on local pests sharing common natural enemies. Biocontrol agents usually used against whiteflies may also prey upon T. absoluta and this could alter the dynamics of local pest populations. We evaluated possible resource competition and predator‐mediated interactions in a system involving one mirid predator Macrolophus pygmaeus and two pests, T. absoluta and a local whitefly, Bemisia tabaci, on greenhouse tomatoes. Results showed that both resource competition and predator‐mediated interactions occurred simultaneously. In the presence of the shared predator, there was a short‐term positive effect of T. absoluta on B. tabaci [up to 5.9‐fold increase of B. tabaci juveniles (egg + larvae) after four weeks]. However, in the long‐term there was a negative predator‐mediated interaction of T. absoluta on B. tabaci, i.e., after ten weeks the density of B. tabaci was 7.3‐fold lower in the presence of the invasive pest. We emphasize the critical role of generalist predators in managing both local and invasive alien pest populations and that the strength and direction of predator‐mediated indirect interactions can depend on the time scale considered.

Invasive pest species may strongly affect biotic interactions in agro-ecosystems. The ability of generalist predators to prey on new invasive pests may result in drastic changes in the population dynamics of local pest species owing to predator-mediated indirect interactions among prey. On a short time scale, the nature and strength of such indirect interactions depend largely on preferences between prey and on predator behavior patterns. Under laboratory conditions we evaluated the prey preference of the generalist predator Macrolophus pygmaeus Rambur (Heteroptera: Miridae) when it encounters simultaneously the local tomato pest Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) and the invasive alien pest Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae). We tested various ratios of local vs. alien prey numbers, measuring switching by the predator from one prey to the other, and assessing what conditions (e.g. prey species abundance and prey development stage) may favor such prey switching. The total predation activity of M. pygmaeus was affected by the presence of T. absoluta in the prey complex with an opposite effect when comparing adult and juvenile predators. The predator showed similar preference toward T. absoluta eggs and B. tabaci nymphs, but T. absoluta larvae were clearly less attacked. However, prey preference strongly depended on prey relative abundance with a disproportionately high predation on the most abundant prey and disproportionately low predation on the rarest prey. Together with the findings of a recent companion study (Bompard et al. 2013, Population Ecology), the insight obtained on M. pygmaeus prey switching may be useful for Integrated Pest Management in tomato crops, notably for optimal simultaneous management of B. tabaci and T. absoluta, which very frequently co-occur on tomato.

Transmission blocking vaccines (TBV) which aim to control malaria by inhibiting human-to-mosquito transmission show considerable promise though their utility against naturally circulating parasites remains unknown. The efficacy of two lead candidates targeting Pfs25 and Pfs230 antigens to prevent onwards transmission of naturally occurring parasites to a local mosquito strain is assessed using direct membrane feeding assays and murine antibodies in Burkina Faso. The transmission blocking activity of both candidates depends on the level of parasite exposure (as assessed by the mean number of oocysts in control mosquitoes) and antibody titers. A mathematical framework is devised to allow the efficacy of different candidates to be directly compared and determine the minimal antibody titers required to halt transmission in different settings. The increased efficacy with diminishing parasite exposure indicates that the efficacy of vaccines targeting either Pfs25 or Pfs230 may increase as malaria transmission declines. This has important implications for late-stage candidate selection and assessing how they can support the drive for malaria elimination.

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