Natural enemy enhancement and botanical insecticide source: a review of dual use companion plants

Intensive agriculture, which is associated with heavy inputs of synthetic insecticides, has serious ecological impacts, leading to loss of vital ecosystem services including insect-mediated pest suppression. In recent years, efforts have been made towards obtaining safer options to chemical insecticides for sustainable pest management. Habitat manipulation is apart of conservation biological control which aims at providing floral resources, alternative prey and shelter to predators and parasitoids to enhance and sustain natural pest suppression. The use of plant extracts as botanical insecticides is also an important provisioning ecosystem service. Selection of plant species for habitat manipulation has focused mainly on plants with suitable floral qualities to support natural enemies. To increase the benefits, habitat manipulation plants that can provide multiple ecosystem services in addition to floral resources would be an ideal. In this review, we focus on the potential of achieving the dual ecosystem services of bioinsecticidal source plants in addition to the provision of floral resources from selected plant species. Our literature search found 283 plants species from 44 plant families that have been involved in habitat manipulation studies. Fifteen of these plant families have species that have been exploited for their insecticidal properties. Three families, Apiaceae, Asteraceae and Lamiaceae, have the largest number of species that have been used for both habitat manipulation and botanical insecticides. Of the four most popular habitat manipulation plants, alyssum Lobularia maritime (L.) Desv. (Brassicaceae), buck wheat Fagopyrum esculentum Moench (Polygonaceae), coriander Coriandrum sativum L. (Apiaceae) and phacelia Phacelia tanacetifolia Benth. (Boraginaceae), buckwheat and coriander have been used for insecticidal purposes whilst no records exist of phacelia and alyssum as botanical insecticide species. There is great potential for identifying plant species that can support natural enemies as well as providing potent plant extracts as botanical insecticides by selecting species from the Apiaceae, Asteraceae and Lamiaceae families.