Studies were conducted in farmer's field, Lambwe School of the Deaf, and Mbita Point Field Station of ICIPE (ICIPE-Mbita) in western Kenya during the long rains of 2001 and 2002 to assess the impact of a diversionary stemborer management strategy on the pest's predators. Treatments consisted of a maize monocrop (control) and an intercrop of maize and desmodium, Desmodium uncinatum Jacq., with Napier grass, Pennisetum purpureum (Schumach), as trap crop around the field (‘push-pull’) in the farmer's field and Lambwe School of the Deaf. Sudan grass, Sorghum vulgare sudanense (Pers.), was used in place of Napier on the station. A combination of sticky traps, direct observation and hand-collection methods were employed. Predator groups encountered included 12 families from 7 insect orders and 4 families from one arachnid order, with most of the foregoing represented in both maize monocrop and ‘push-pull’ plots. A Cheilomenes sp. and Chrysopa sp. were, however, recovered from ‘push-pull’ plots only. Ants, earwigs and spiders were the main predators encountered. Both overall and individual group populations of these predators as well as ant diversity were significantly higher in ‘push-pull’ than monocrop plots in all the sites during the vegetative, flowering and mature maize growth stages (P < 0.05, t-test). The results thus indicate a numerical enhancement of stemborer predators by use of this habitat management system.

Maize is the principal food and cash crop for millions of people in the predominantly mixed crop-livestock farming systems in Kenya. Stemborers and striga (Striga hermonthica) are major constraints to increased maize production in eastern Africa. An intercropping and trap crop system has been developed, using a ‘push-pull’ strategy, for the control of stemborers in small scale maize farming systems. The ‘push-pull’ strategy involves trapping stemborers on highly susceptible trap plants (pull) and driving them away from the crop using repellent intercrops (push). Napier grass (Pennisetum purpureum Schumach) and Sudan grass (Sorghum vulgare sudanense Stapf.) are used as trap plants, whereas molasses grass (Melinis minutiflora Beauv.) and two species of desmodium (Desmodium uncinatum Jacq. and Desmodium intortum Urb.) repel ovipositing stemborers. The integrated ‘push-pull’ strategies were shown to increase parasitism of stemborers through attraction of parasitoids to one of the intercrops, molasses grass. The leguminous intercrop, silver leaf desmodium, drastically reduced damage to maize by the parasitic weed, striga. This aspect was further investigated and developed for integration with stemborer control. On-farm trials with farmers in Kenya have shown significant yield increases in maize farming.

The stemborers Busseola fusca (Lepidoptera: Noctuidae) and Chilo partellus (Lepidoptera: Crambidae) are important pests of maize and sorghum in South Africa. A habitat management system for these pests is being developed in the Northern Province of South Africa. This management system is similar to the one used in eastern Africa, where host and non-host plants of stemborers are used to repel moths away from the main crop and attract them to highly attractive trap plants. To identify possible trap crops, a survey of wild host plants of stemborers was undertaken in the Northern Province of South Africa and several new host plants were recorded. As a possible trap crop for stemborers, various Napier grass (Pennisetum purpureum) varieties were evaluated for oviposition preference by Ch. partellus moths and subsequent larval survival on those varieties. Few larvae survived longer than 15 days after inoculation onto Napier grass plants. A survey was conducted of farming practices that would affect the adoption of habitat management strategies. The high usage of tractors for ploughing may have a negative effect on adoption of perennial intercrops in a habitat management system. The common practice of free grazing animals also reduced the fodder value and benefit of trap crops. The value of Napier grass does not only lie in its use as trap crop but also as a measure to limit soil erosion and as animal feed.

Field trials in Kenya demonstrated that the forage grass, Sorghum vulgare sudanense (Sudan grass) attracted greater oviposition by stemborers than cultivated maize, resulting in significant increase in maize yield. On the other hand, the non-host forage plant, Melinis minutiflora (molasses grass), when inter-cropped with maize, repelled gravid stemborer females from ovipositing on maize, resulting in significant reduction in stemborer infestation. Using these trap- and repellent gramineous plants, a novel pest management approach based on a ‘push-pull’ or stimulo-deterrent diversionary strategy is being developed where stemborers are repelled from the food crop and are simultaneously attracted to a discard or trap crop. The plant composition and permanence of habitat surrounding maize fields also influence the abundance of natural enemies that invade agroecosy stems once a pest population is present. It may be advantageous to promote the growth of native Gramineae and other wild plants which minimise, or even suppress, population growth of pests during non-cropping seasons, but still provide a suitable habitat for natural enemies.