Novel Semiochemical-Based Management of Fall Armyworm (FAW) in Brazil using Companion Crops

In Brazil, maize is an important crop, providing a source of carbohydrates, vitamins and minerals in the diet. Many small farms in Brazil are run as a family business and provide subsistence for the family, and therefore economic prosperity and survival can depend entirely on the success of the maize harvest. Unfortunately, many insect pests attack maize plants, causing severe crop losses from insect damage.
Although maize can be protected from pests by pesticides and even some alternative pest management tools eg pheromones that affect pest behaviour, most if not all of these options are unaffordable for smallholder farmers and there is no other management option available. It is vital that new strategies to defence vital maize crops are developed.
Insect pests use their sense of smell to detect and locate suitable host plants for feeding and egg-laying. The odour of host plants comprises of attractive volatile compounds, but when pests start to damage the host plant, the odour changes as plants defend themselves and they become unattractive to the pests. A further development of this phenomenon is that the natural enemies of pests are 'tuned in' to the odour produced by plants when they are damaged by pests. These ecological interactions can be exploited in crop protection by using attractive odours to pull pests into traps, using repellent odours to push pests away from crop plants and attract natural enemies (predators and parasitic wasps) for control, or even using both sets of odours at the same time as part of a push-pull strategy.
The use of synthetic attractive and repellent odours in pest management has been extensively explored, but for smallholder farmers, even this technology is unaffordable. A further development of the use of attractive and repellent odours is that they can be delivered by plants, with crop plants being selected or engineered to produce repellent odours and companion plants being selected to produce attractive odours. This companion cropping approach has been adopted with outstanding success in Africa for moth pest management on cereal crops, with more than 100,000 smallholder farms adopting it to date. One of the key reasons for success is that the approach fits with traditional mixed cropping systems used in smallholder farming.
Experiments under controlled conditions using varieties of a plant called maize and a moth commonly known as Fall Armyworm (FAW) showed that certain varieties changed their odour more quickly and powerfully than others in response to FAW damage and became attractive to parasitic wasps. Furthermore, neighbouring undamaged maize plants that were exposed to the odour of FAW-damaged maize became more prepared (activated) to respond to FAW damage, should the pest start to spread away from damaged plants. If we can identify this response to FAW damage in maize varieties that are popular in maize-growing regions in Brazil, and identify companion plants that are more attractive to FAW than maize and can emit the defence activating odour when damaged by FAW, then we have an opportunity to develop a companion cropping approach for FAW management in maize crops in Brazil.
We will screen, in the laboratory, maize varieties that are popular in maize-growing regions in Brazil with respect to their defence response to FAW damage and attractiveness to a natural enemy; screen in the field, maize varieties that have been identified as responding to FAW damage and attracting natural enemies, for enhanced presence of natural enemies and suppression of FAW populations; screen, in the laboratory, companion plants with respect to their attractiveness to FAW and ability to activate defence in neighbouring maize plants leading to natural enemy attraction; put combinations of identified maize lines and companion plants together in the field and screen for enhanced presence of natural enemies and suppression of FAW populations; show the new technology to smallholder farmers.