Is it possible to manage pests and pesticide resistance in heterogeneous landscapes?

Associate Editor Juan Corley explores the challenge of creating environmentally friendly pest management solutions. Does the recent work of Zhou et al. on self-limiting transgenic insects point us in the right direction?

Food production is strongly dependent on successful pest management. Since the 1970s, and partly as a consequence of increasing problems with the mass use of pesticides, Integrated Pest Management (IPM) has become the flagship of pest control.  Still, the evolution of resistance in pest populations. due to strong selection from several management approaches, remains a serious problem for which there are few mitigation strategies. The use of transgenic insects carrying lethal, self‐limiting genes that can reduce pest insect populations appears as promising way to slow the process.

The application of self-limiting transgenic insects is conceptually comparable to the “’sterile-insect technique’ in that it comprises the release of large numbers of engineered males that, upon mating with wild females, leave no viable offspring. In this way, pest populations can be driven to low numbers, exposing them to, for instance, Allee effects. The method may also allow integration of insecticide-susceptible alleles into the target populations, slowing the evolution of resistance. The transgenes are self-limiting because they are designed to die and disappear from the environment post-release.

Diamondback moth
The diamondback moth has developed resistance to many of the common chemical pesticides (Photo from Wikimedia Commons)

However, a major drawback of this strategy, and common with sterile-insect release programmes, is that effectiveness depends on the scale of operation. Programmes are typically implemented over large areas, which suggests significant costs But, if focus is switched to resistance management, short-term release programmes could, in theory, work.  Even though agricultural landscapes are often highly heterogeneous and patchiness can accelerate the evolution of resistance in the pest population, transgenic insect releases focused on particular subpopulations may also reduce pest populations. These are, in essence, the main questions tackled by Zhou et al. who use as their biological model, a widespread pest of crucifers, the Diamondback moth Plutella xylostella.

Using experimental cages, the authors manipulated the numbers of transgenic insects released into known wild populations. The experiments simulated area-wide vs targeted release strategies.  Their response variable was the survival of insects to a toxin diet, and bioassays of phenotypic resistance under controlled conditions were also carried out, as a measure of population insecticide resistance.

Zhou et al neatly show that focused, small releases of transgenic insects could be a viable pest management strategy, even at the landscape scale, as they can affect source to sink population frequencies. This is an important finding, which would need scaling up to field conditions, but suggests that we may not need to rely as heavily on pesticides in the near future as we do today. Still, area-wide treatments seem hard to beat when it comes to resistance management. A critical issue is that practitioners should be able to identify source populations in the agricultural landscape, an aspect that needs clarification. Other issues that affect success are the dispersal capability of the target pest, and the timing of mating as related to dispersal. Basic, pest-specific biological studies are of course still needed.

Environmentally friendly pest management is a standing challenge. We need much more research in this field, which must provide sound strategies with real-life applicability. Considering insecticide resistance evolution and population ecological concepts together, as illustrated by Zhou et al´s work, seems a clever way to go.

Read the full open access article, The application of self‐limiting transgenic insects in managing resistance in experimental metapopulations in issue 56:3 of Journal of Applied Ecology.

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