Fall armyworm, Spodoptera frugiperda, is a serious invasive pest in Africa but “Push-Pull” companion cropping can substantially reduce infestation. Here, we elucidate the underpinning chemical ecology mechanisms. We hypothesized that companion crop volatiles repel herbivores (push) while attracting natural enemies (pull). Headspace volatiles collected from companion plants (Desmodium intortum, Desmodium uncinatum, Brachiaria Mulato II) were used in bioassays and electrophysiological recordings with S. frugiperda and parasitoid wasps. Insect populations, plant damage and herbivore parasitism were assessed in field plots. Coupled GC-electroantennogram (GC-EAG) recordings showed robust responses to certain aromatic and terpenoid volatile compounds. In wind tunnel bioassays, maize volatiles mixed with Desmodium volatiles were less attractive to moths than maize alone. In oviposition bioassays, S. frugiperda laid significantly fewer eggs on maize when Desmodium volatiles were present. Conversely, in an olfactometer bioassay, parasitoid wasps were attracted to the scent of both Desmodium spp. (intercrop) and the Brachiaria border crop. Our data provide evidence of the mechanisms underpinning reduced S. frugiperda infestation in the Push-Pull companion cropping system, i.e., volatiles from companion crops repel S. frugiperda while attracting its parasitoid natural enemies. These findings explain why Push-Pull field plots had fewer S. frugiperda larvae and lower crop damage than monocropped maize.

The cereal stemborer Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) is a major insect pest of sorghum (Sorghum bicolor L. Moench) and maize (Zea mays L.) in Africa. Trap cropping systems have been shown to be a valuable tool in management of this pest. To optimize trap cropping strategies, an understanding of host‐plant preference for moth oviposition and host suitability for larval survival on potential trap plants is a prerequisite. Therefore, we assessed seven brachiaria accessions (Poaceae) for preference by C. partellus moths and subsequent larval performance. In two‐choice tests with a local open‐pollinated maize variety (cv. Nyamula), significantly higher numbers of eggs were deposited on brachiaria accessions Marandu, Piata, and Xaraes than on maize, whereas fewer eggs were recorded on plants of Mulato II, Mulato I, and Cayman. There was a significant and negative correlation between the trichome density on plant leaves and C. partellus oviposition preference for brachiaria. In addition to poor larval performance on brachiaria, there was no clear ranking in the accessions regarding larval orientation, settling, arrest, and food ingestion and assimilation. First instars did not consume leaf tissues of brachiaria plants but consumed those of maize, which also suffered more stem damage than brachiaria plants. No larvae survived on brachiaria plant tissue for longer than 5 days, whereas 79.2% of the larvae survived on maize. This study highlights the preferential oviposition of C. partellus on brachiaria plants over maize and the negative effects that these accessions have on subsequent larval survival and development. Our findings support the use of brachiaria as a trap crop for management of C. partellus through a push‐pull technology.

Brachiaria (Urochloa) is a genus, common name brachiaria, of forage grasses that is increasingly transforming integrated crop-livestock production systems in East Africa. A study was undertaken to (i) assess smallholder farmers’ perception on benefits of brachiaria in cereal-livestock production, (ii) identify brachiaria production constraints, and (iii) identify farmer preferred brachiaria genotypes. A multi-stage sampling technique was adopted for sample selection. Data were collected through semi-structured individual questionnaire and focus group discussions (FGDs). The study areas included Bondo, Siaya, Homabay and Mbita sub-counties in Western Kenya and the Lake zone of Tanzania. A total of 223 farmers participated in individual response questionnaires while 80 farmers participated in the FGDs. The respondents considered brachiaria mainly important in management of cereal pests (70.4% of respondents) and as an important fodder (60.8%). The major production constraint perceived by both male and female respondents is attacks by arthropods pests (49.2% and 63%, respectively). Spider smites had been observed on own farms by 50.8% of men and 63.1% of women, while sorghum shoot flies had been observed by 58.1% of men and 67.9% of women. These pests were rated as a moderate to severe problem. Xaraes was the most preferred genotype, followed by Mulato II and Piata. These genotypes are important in developing new crop pest management strategies, such as push-pull, and for relatively rapid improvements in crop management and yield increases, particularly in developing countries.