Dormancy Management to Enable Mass-rearing and Increase Efficacy of Sterile Insects and Natural Enemies

Insect pests cause significant and widespread damage worldwide. Insecticide application remains the predominant method of controlling these pests. According to FAO, 30-40 % of agricultural production is lost to pre-harvest and post-harvest infestations mainly caused by insect pests. Despite growing worldwide dependence on agrochemicals, suppression of pest populations is frequently inadequate. In addition, due to regulation, pest resistance, and environmental and human health concerns, there is an increasing demand for the replacement of the intensive use of these chemicals by environmentally friendly, effective and sustainable methods within integrated pest management approaches. Chief among these are biological control applications based on the use of sterile insects and natural enemies.

Most insects face times of the year when reproduction or development are suppressed due to a lack of resources or unfavourable environmental conditions. Dormancy responses have evolved to mitigate the stresses of these unfavourable times and to synchronize insect life cycles with favourable periods. Dormancy responses can include both pre-programmed, hormonally mediated diapause, and also quiescence induced directly by the environment (e.g. low temperatures, drought, lack of hosts, etc.). Quiescence is a state of developmental arrest that can occur in any life stage. In contrast, diapause is a stage-specific developmental arrest that can be either facultative (determined by token stimuli) or obligate (occurring regardless of prevailing environmental conditions).

Many univoltine pest species have an obligatory diapause that synchronizes them with resource availability. For such univoltine insect pest species, the sterile insect technique (SIT) and augmentative natural enemy control have been neither practical nor possible due to obligatory diapause responses that prevent or interfere with continuous mass rearing. Examples include the European cherry fruit fly, apple maggot fly, Chinese citrus fruit fly, Russian melon fly, and processionary moths. Although obligatory diapause has been a major roadblock to developing biological control programs for many pests, current research suggests that there are approaches that can potentially disrupt obligatory diapause and facilitate mass rearing. Four approaches appear particularly promising for circumventing the challenges of obligate diapause, including: (1) simple environmental manipulations, such as thermal shock, (2) chemical or hormonal treatments, such as application of organic solvents, (3) choosing geographical populations without diapause or artificial selection for nondiapausing strains within populations, and (4) genetic modification by mutagenesis or transgenesis of critical genes for diapause. Successfully circumventing obligate diapause with any of these approaches, or a combination thereof, would provide new opportunities for effectively mass rearing of important pest species.

While obligate diapause is an obstacle in some cases, two aspects of dormancy responses can be effectively exploited to improve the efficacy of biological control programs.

First, dormancy can be used to stockpile mass-reared insects and to time the supply of biological control agents to coincide with seasonal demand for releases. The ability to synchronize the supply of control agents with demand is critical for the growing biological control industry. Furthermore, inducing dormant states opens up new opportunities for either enhancing classical cryopreservation of embryos (in liquid nitrogen) or developing new methods for long-term cold storage of other life stages, such as larvae or pupae. Development of such techniques would make it feasible to maintain strains over the long term without compromising the genetic integrity of those strains, while avoiding the efforts and costs involved in continuous rearing. This ability to maintain stocks without continuous rearing is especially important when considering the rapid accumulation of mutant and transgenic strains in entomological research laboratories.

Second, increased stress tolerance is often a hallmark of dormancy that could be exploited in biological control applications. The efficacy of biological control, including sterile insect programs and natural enemy releases, is affected by the quality of insects released into the field. Poor performance of insects used in field releases can be a product of stresses experienced at multiple points during the production, marking, irradiation, shipping, and release process. The ability to specifically induce dormant states, including either diapause or quiescence, could potentially reduce the above stresses, thereby improving the performance of individuals in field releases. For example, some diapausing insects are known to be resistant to low-level irradiation. Perhaps diapause could be exploited to reduce off-target irradiation damage, outside of germ-line genomic DNA, and improve the performance of sterile insects. Similarly, insects are exposed to mechanical disturbance, hypoxia, and thermal stress during shipping that may be mitigated by inducing dormant states prior to shipping.

Beyond applications to existing biological control tactics, there is an opportunity to develop novel strategies for controlling pest populations by managing diapause and dormancy responses. For example, new approaches to prevent diapause, terminate diapause, or prolong diapause could be exploited to desynchronize insects from favourable environmental conditions, thus inducing ‘ecological suicide’in pest populations.

Developing dormancy management tools could be important for biological control involving sterile insects or natural enemy releases. Six key questions should be addressed:

  • Can dormancy responses be used to manage insect life cycles to enable or improve the efficacy of mass rearing?
  • Can dormancy responses be used to maintain the genetic integrity of laboratory strains?
  • Can dormancy responses be used to enable or enhance the shelf life of sterile insects and natural enemies while making them available for release upon demand?
  • Can dormancy responses be used to reduce radiation injury and enhance sterile insect performance?
  • Can dormancy responses be managed to decrease shipping-related damage and enhance post-shipping performance of biological control agents?
  • Can studying dormancy responses foster the development of novel approaches for insect pest management, for example ‘ecological suicide’?

Participants:

Fourteen participants: Argentina, Bangladesh, Belgium, Canada, China, Czech Republic, Denmark, France, Greece, Japan, Mexico, South Africa, United Kingdom, United States of America.

Reports:

Project Officer:

Rui Cardoso Pereira