Push-Pull: Chemical Ecology-Based Integrated Pest Management Technology

Abstract

Lepidopterous stemborers, and parasitic striga weeds belonging to the family Orobanchaceae, attack cereal crops in sub-Saharan Africa causing severe yield losses. The smallholder farmers are resource constrained and unable to afford expensive chemicals for crop protection. The push-pull technology, a chemical ecology- based cropping system, is developed for integrated pest and weed management in cereal-livestock farming systems. Appropriate plants were selected that naturally emit signaling chemicals (semiochemicals). Plants highly attractive for stemborer egg laying were selected and employed as trap crops (pull), to draw pests away from the main crop. Plants that repelled stemborer females were selected as intercrops (push). The stemborers are attracted to the trap plant, and are repelled from the main cereal crop using a repellent intercrop (push). Root exudates of leguminous repellent intercrops also effectively control the parasitic striga weed through an allelopathic mechanism. Their root exudates contain flavonoid compounds some of which stimulate germination of Striga hermonthica seeds, such as Uncinanone B, and others that dramatically inhibit their attachment to host roots, such as Uncinanone C and a number of di-C-glycosylflavones (di-CGFs), resulting in suicidal germination. The intercrop also improves soil fertility through nitrogen fixation, natural mulching, improved biomass, and control of erosion. Both companion plants provide high value animal fodder, facilitating milk production and diversifying farmers' income sources. The technology is appropriate to smallholder mixed cropping systems in Africa. Adopted by about 125,000 farmers to date in eastern Africa, it effectively addresses major production constraints, significantly increases maize yields, and is economical as it is based on locally available plants, not expensive external inputs.

Volatile Semiochemical Mediated Plant Defense in Cereals: A Novel Strategy for Crop Protection

“…Our recent study on a wide range of maize germplasm revealed some maize genotypes emit HIPVs attractive to egg and larval parasitic wasps at the egg-laying stage of insect attack [27,28]. This represents a sophisticated defence response which provides timely and effective biological control early on, before much damage is caused by the hatching larvae [11,28]. Some plant species constitutively release volatile semiochemicals that repel insect pests and attract natural enemies of the herbivore [29,30].…”

“…In addition to producing repellent volatile semiochemicals that push away the stemborer moths, the root exudates of Desmodium spp have been shown to effectively suppress the parasitic weed, Striga spp. through an allelopathic mechanism [11,30].…”

“…Moreover, Napier grass tissues produce a sticky sap in response to feeding by the stemborer larvae which traps them causing significant mortality [11,30]. In this way, it is possible to divert stemborers from the main crop and significantly reduce damage caused by the pests.…”

“…A potential to improve plant resistance against insect pests by exploiting constitutive and inducible plant volatile semiochemicals has been demonstrated in agricultural settings [10,11]. Moreover, there is an increasing interest for semiochemicals based pest management in recent years, due to ecological and environmental costs associated with use of broad-spectrum insecticides.…”

“…Unlike chemical insecticides, volatile semiochemicals are difficult for insects to develop resistance against, and work by a non-toxic mode of action through modifying the behaviour of the pest or its natural enemies to the detriment of the crop pest [12,13]. Furthermore, they are non-persistent, species-specific, cost-effective, and environmentally safe [11]. This review presents concise summary about plant derived volatile semiochemicals and their applications in improving plant resistance against insect pests drawing practical examples from two crop protections strategies, namely genetic engineering (GM) and a stimulo-deterrent diversionary (push-pull) strategy.…”