The push-pull intercrop Desmodium does not repel, but intercepts and kills pests

Over two decades ago, an intercropping strategy was developed that received critical acclaim for synergizing food security with ecosystem resilience in smallholder farming. The push-pull strategy reportedly suppresses lepidopteran pests in maize through a combination of a repellent intercrop (push), commonly Desmodium spp., and an attractive, border crop (pull). Key in the system is the intercrop's constitutive release of volatile terpenoids that repel herbivores. However, the earlier described volatile terpenoids were not detectable in the headspace of Desmodium, and only minimally upon herbivory. This was independent of soil type, microbiome composition, and whether collections were made in the laboratory or in the field. Furthermore, in oviposition choice tests in a wind tunnel, maize with or without an odor background of Desmodium was equally attractive for the invasive pest Spodoptera frugiperda. In search of an alternative mechanism, we found that neonate larvae strongly preferred Desmodium over maize. However, their development stagnated and no larva survived. In addition, older larvae were frequently seen impaled and immobilized by the dense network of silica-fortified, non-glandular trichomes. Thus, our data suggest that Desmodium may act through intercepting and decimating dispersing larval offspring rather than adult deterrence. As a hallmark of sustainable pest control, maize-Desmodium push-pull intercropping has inspired countless efforts to emulate stimulo-deterrent diversion in other cropping systems. However, detailed knowledge of the actual mechanisms is required to rationally improve the strategy, and translate the concept to other cropping systems

Assessment of the impact of the Black Coffee Twig Borer, Xylosandrus compactus infestation in Ugandan small-scale coffee gardens, and the potential of its suppression through repellence in conjunction with push-pull technology

Coffee production in Uganda is an important means of income for smallholder farmers and extensively supports rural livelihoods. It contributes to about 20- 30% of the annual export revenue of the country. Yet, coffee production is challenged by many factors. Of these, the black coffee twig borer (BCTB), Xylosandrus compactus, is arguably the most important. In this study we conducted semi-structured interviews and online questionnaires of stakeholders: farmers and officials, to assess the perceptions and knowledge levels about BCTB in relation to other coffee-related threats. We also assessed the level of information flow prevailing amongst the stakeholder groups. We did these surveys in the Namasagali sub-county of the Kamuli district. The results show awareness among both groups of this pest and its devastating impacts on coffee production. However, the levels of understanding varied. All the farmers implemented the recommended control measures. They expressed the need for improvements and additional technology since BCTB infestations have been increasing over the years. Control using insecticides were frequently proposed as a way of handling BTCB infestations, even though insecticides are relatively ineffective and would have disastrous impacts on the biodiversity-rich coffee production in agroforestry settings. Therefore, environmentally and economically sustainable alternatives are necessary to avoid the serious transition of the farmers from presently organic methods to adopting unsustainable technologies. We complemented our interview surveys with field trials to test a novel agroecological approach for the management of BCTB based on the “push-pull” principle of cropping systems. This system uses attractants and repellents to divert pests away from the crop. We tested the possibility of using verbenone, an anti-aggregation signal of other bark beetles, for use in integrated BCTB control. We used a wax-based emulsion, SPLAT, for the slow-release of verbenone in the field. We found that a single 2 g dollop of SplatVerb per tree reduced BCTB infestations by 60% in small coffee stands. Our results indicate the potential of managing BCTB infestations using push-pull, showing that SplatVerb can function as the ‘push’ component. Future studies should increase the scale of the intervention trials, and test locally available repellents such as aromatic plant extracts. Additionally, test the push-pull concept through combining the repellent with e.g. traps containing attractants. Furthermore, research on mutual expectations and identifying obstacles and possibilities to suggest possible improvements in the stakeholder communication chain to support the dissemination of sustainable innovations to combat BCTB and other threats to coffee production under agroforestry settings