Importance of Collection Overhangs on the Efficacy of Exclusion Fences for Managing Cabbage Flies (Diptera: Anthomyiidae)

Fine nylon mesh fences (135 cm high) with varying lengths of downward-sloping collection overhangs were evaluated for efficacy in excluding the female cabbage flies Delia radicum (L.) from plots of radish, Raphanus sativus (L.). During three trials conducted in 1994 and 1995, fences without overhangs, fences with 12.5-cm overhangs, or fences with 50-cm overhangs were tested against fences with standard 25-cm overhangs and unfenced control plots. In fenced plots with standard 25-cm overhangs, the mean number of D. radicum females caught on yellow sticky traps placed within plots was 85% less than those caught in corresponding control plots. The mean numbers of D. radicum females caught in fenced enclosures with no overhangs, 12.5-cm overhangs, or 50-cm overhangs, were 61, 67, and 94% less than those caught in corresponding control plots, respectively. The mean proportion of radishes damaged by D. radicum larvae inside enclosures with 25-cm overhangs was 62% less than in corresponding control plots. The mean proportions of radishes damaged inside fences with no overhangs, 12.5-cm overhangs, or 50-cm overhangs were 33, 59, and 81% less than those caught in corresponding control plots, respectively. Results are discussed in terms of defining an appropriate fence design for commercial use

Exploiting phytochemicals for developing sustainable crop protection strategies to withstand climate change: example from Africa

Africa suffers chronic food insecurity resulting from ravaging effects of insect pests, weeds and poor soil fertility, with rising poverty and increasingly dry and hot weather conditions associated with climate change further aggravating this situation. Scientists at the International Centre of Insect Physiology and Ecology (icipe) together with national and international partners have developed a platform technology, ‘push–pull’, based on locally available companion plants for integrated management of these constraints by exploiting innate plant defence systems including secondary metabolism. This involves intercropping cereal crops, the main staple and cash crops for millions of smallholder farmers in the continent, with forage legumes in the genus Desmodium and planting Napier grass as a trap plant around this intercrop. Stemborer pests are attracted to Napier grass (pull) and are repelled from the main cereal crop by the repellent desmodium (push). Desmodium root exudates effectively control the parasitic striga weed by causing abortive germination and also improve soil fertility through nitrogen fixation, provide natural mulching and improve biomass. Both companion plants provide high-value animal fodder, facilitate milk production and fetch additional income for farmers. The technology is appropriate to smallholder mixed cropping systems in sub-Saharan Africa (SSA) as it effectively addresses major production constraints and significantly increases cereal yields. It is currently being practiced by about 90,000 smallholder farmers in eastern Africa and has also been adapted to harsh conditions associated with climate change by incorporating drought-tolerant companion plants. This chapter highlights the developmental process of the technology and its benefits in SSA in the face of climate change

Exploiting chemical ecology for developing novel integrated pest management strategies for Africa

Push-pull, a novel approach for integrated management of insect pests, weed and soil fertility, was developed through the exploitation of chemical ecology and agro-biodiversity to address agricultural constraints facing millions of resource-poor African farmers. The technology was developed by selecting appropriate plants that naturally emit signalling chemicals (semiochemicals) and influence plant-plant and insect-plant interactions. Plants highly attractive for egg laying by lepidopteran cereal stemborer pests were selected and employed as trap crops, to draw pests away from the main cereal crops. Among these, Pennisetum purpureum produced significantly higher levels of volatile cues (stimuli), used by gravid stem borer females to locate host plants, than maize (Zea mays) or sorghum (Sorghum bicolor). Despite its attractiveness to stemborer moths, P. purpureum supported minimal survival of the pests’ immature stages. Plants that repelled stem borer moths, notably Melinis minutiflora and forage legumes in the genus Desmodium, were selected as intercrops, which also attracted natural enemies of the pests through emission of (E)-β-ocimene and (E)-4,8-dimethyl-1,3,7-nonatriene. Desmodium intercrop suppressed parasitic weed, Striga hermonthica, through an allelopathic mechanism. Their root exudates contain novel flavonoid compounds which stimulate suicidal germination of S. hermonthica seeds and dramatically inhibit its attachment to the host roots. We identified and selected new drought- and temperature-tolerant trap [Brachiaria ( B. brizantha × B. ruziziensis ) cv. mulato] and intercrop plants (Desmodium, e.g. D. intortum) suitable for drier agroecologies. The new trap and intercrop plants also have appropriate chemistry in controlling stemborers, a new invasive pest, fall armyworms and parasitic striga weeds. Opportunities for semiochemical delivery by companion plants, including plant-plant signalling and early herbivory alert, are explored for developing future smart integrated pest management (IPM) strategies