Rampant increase and diversification of synthetic pesticides poses health, environmental, and livelihood risks especially to smallholder farmers who dominate agriculture in sub-Saharan Africa. Legal ...mechanisms for regulating pesticides, although important, have not fully addressed the dangers of ecological services disruptions due to accumulation of different pesticides over time. Legal mechanisms also are not well suited to developing countries because of weak monitoring and enforcement capacity. Understanding the role of other accountability mechanisms in farming, driven by norm leaders in the community, is thus of paramount importance. We investigated the effectiveness of a traditional accountability mechanism, i.e., local councils of elders known as the Njuri Ncheke, in controlling pesticide use in khat (Catha edulis). Khat samples were taken from traditional production systems in which these councils have influence and from commercial production systems lacking the councils' influence. The samples were analyzed for pesticide residues using liquid chromatography mass spectrometry. Individual farmer interviews were also carried out, inquiring about the influence of the Njuri Ncheke on the local community and on pesticide use in crop production. Our results show that a variety of agrochemical pesticides are being used by smallholder khat farmers and that local Njuri Ncheke councils have had success in limiting pesticide use, arguably more success than any government agency working to control pesticides on any local crop. These results show the potential of public accountability through traditional institutions like councils of elders and the role they can play in complimenting legal regulation mechanisms for successful pesticides management in agroecosytems.
Intercropping is drawing increasing attention as a strategy to increase crop yields and manage pest pressure, however the mechanisms of associational resistance in diversified cropping systems remain ...controversial. We conducted a controlled experiment to assess the impact of co-planting with silverleaf Desmodium (
Desmodium uncinatum
) on maize secondary metabolism and resistance to herbivory by the spotted stemborer (
Chilo partellus
). Maize plants were grown either in the same pot with a
Desmodium
plant or adjacent to it in a separate pot. Our findings indicate that co-planting with
Desmodium
influences maize secondary metabolism and herbivore resistance through both above and below-ground mechanisms. Maize growing in the same pot with a
Desmodium
neighbor was less attractive for oviposition by spotted stemborer adults. However, maize exposed only to above-ground
Desmodium
cues generally showed increased susceptibility to spotted stemborer herbivory (through both increased oviposition and larval consumption). VOC emissions and tissue secondary metabolite titers were also altered in maize plants exposed to
Desmodium
cues, with stronger effects being observed when maize and
Desmodium
shared the same pot. Specifically, benzoxazinoids were strongly suppressed in maize roots by direct contact with a
Desmodium
neighbor while headspace emissions of short-chain aldehydes and alkylbenzenes were increased. These results imply that direct root contact or soil-borne cues play an important role in mediating associational effects on plant resistance in this system.
Attack of plants by herbivorous arthropods may result in considerable changes to the plant's chemical phenotype with respect to emission of herbivore-induced plant volatiles (HIPVs). These HIPVs have ...been shown to act as repellents to the attacking insects as well as attractants for the insects antagonistic to these herbivores. Plants can also respond to HIPV signals from other plants that warn them of impending attack. Recent investigations have shown that certain maize varieties are able to emit volatiles following stemborer egg deposition. These volatiles attract the herbivore's parasitoids and directly deter further oviposition. However, it was not known whether these oviposition-induced maize (Zea mays, L.) volatiles can mediate chemical phenotypic changes in neighbouring unattacked maize plants. Therefore, this study sought to investigate the effect of oviposition-induced maize volatiles on intact neighbouring maize plants in 'Nyamula', a landrace known to respond to oviposition, and a standard commercial hybrid, HB515, that did not. Headspace volatile samples were collected from maize plants exposed to Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) egg deposition and unoviposited neighbouring plants as well as from control plants kept away from the volatile emitting ones. Behavioural bioassays were carried out in a four-arm olfactometer using egg (Trichogramma bournieri Pintureau & Babault (Hymenoptera: Trichogrammatidae)) and larval (Cotesia sesamiae Cameron (Hymenoptera: Braconidae)) parasitoids. Coupled Gas Chromatography-Mass Spectrometry (GC-MS) was used for volatile analysis. For the 'Nyamula' landrace, GC-MS analysis revealed HIPV production not only in the oviposited plants but also in neighbouring plants not exposed to insect eggs. Higher amounts of EAG-active biogenic volatiles such as (E)-4,8-dimethyl-1,3,7-nonatriene were emitted from these plants compared to control plants. Subsequent behavioural assays with female T. bournieri and C. sesamiae parasitic wasps indicated that these parasitoids preferred volatiles from oviposited and neighbouring landrace plants compared to those from the control plants. This effect was absent in the standard commercial hybrid we tested. There was no HIPV induction and no difference in parasitoid attraction in neighbouring and control hybrid maize plants. These results show plant-plant signalling: 'Nyamula' maize plants emitting oviposition-induced volatiles attractive to the herbivore's natural enemies can induce this indirect defence trait in conspecific neighbouring undamaged maize plants. Maize plants growing in a field may thus benefit from this indirect defence through airborne signalling which may enhance the fitness of the volatile-emitting plant by increasing predation pressure on herbivores.
False codling moth (FCM) Thaumatotibia leucotreta Meyrick (Lepidoptera: Tortricidae) is currently the main pest of phytosanitary concern in international trade, causing rejection and decline of ...horticultural produce from Kenya exported to the European Union (EU). Overreliance on synthetic insecticides to control this pest is ineffective and unsustainable in the long run, whereas continuous use of pesticides results in high levels of residues in the produce. To gather farmers’ knowledge, attitudes, and practices used by smallholder farmers to manage this pest, a field survey was carried out in 10 Capsicum sp. (Solanales: Solanaceae)-producing counties in Kenya. Data were collected using semi-structured questionnaires administered through face-to-face interviews and focus group discussions involving 108 individual farmers, 20 key informants, and 10 focus group discussions. The majority of the respondents (83.33%) were aware of the FCM infesting Capsicum sp. About three quarters of the farmers (76.85%) reported yield losses and unmarketable quality of FCM-infested Capsicum sp. Most farmers interviewed (99.07%) used insecticides as a management tool. In contrast, only 39.81% of the farmers applied integrated pest management strategies including use of biological control agents and intercropping with repellent plants to control this pest. The results show that FCM is perceived as a significant threat to the horticultural industry of Kenya. Training needs for smallholder farmers and key informants to avoid overreliance on synthetic chemical pesticides and to maintain export goals to the EU where identified.
Crucifers and traditional African vegetables (TAVs) are important to smallholders in Kenya and Tanzania, but yield remains below potential due to pests and diseases. Agroecological production methods ...present a nature-based solution to pest and disease management in crucifer and TAV production. We explore the status of farmers’ knowledge, attitudes, and practices regarding agroecological-based production pest management practices. Structured and pretested questionnaires were used to collect data from 1071 vegetable farming households in Kenya and Tanzania. Using descriptive statistics, parametric, and non-parametric analysis, our study revealed that less than 20% of farmers had received training on agroecological-based practices and less than 25% were aware of most of these practices. Among those who were aware of the practices and could confirm their effectiveness less than 12% had adopted them, except for crop rotation and handpicking of pests. This study attributes the low adoption to farmers’ negative attitudes towards the practices. Nonetheless, the study further revealed that training significantly and positively influences the adoption of the practices. Therefore, we recommend that governments and other stakeholders promote targeted awareness campaigns and increase access to training on vegetable production using sustainable pest and disease management practices.
This study sought to evaluate the oviposition responses of Chilo partellus (Lepidoptera: Crambidae) on maize plants exposed to Brachiaria brizantha Stapf following oviposition by C. partellus and ...nonexposed maize. Two Kenyan maize landraces (Jowi and Nyamula), Latin America landrace (Cuba 91) and WH505 (hybrid variety) (control) were studied. The result demonstrated that C. partellus deposited a significantly lower number of eggs and egg batches on Nyamula, Jowi and Cuba 91 maize plants exposed to B. brizantha with C. partellus eggs compared to nonexposed ones and the exposed hybrid variety. This was because they emitted electrophysiologically active compounds such as (E)-4, 8-dimethyl-1, 3, 7-nonatriene, decanal, (E)-caryophyllene, linalool, linalool (plus nananal), E-β-fernesene, methyl salicylate and (3E, 7E)-4, 8, 12-trimethyl-1, 3, 7, 11-tri-decatetraene that deterred C. partellus from ovipositing more eggs on these plants. Therefore, herbivore-induced plant volatiles (HIPVs) of B. brizantha can be employed to protect the maize crop against C. partellus.
Plants can alter nutritional availability, structure, and chemistry of the soil they grow in. These soil changes can positively or negatively influence the growth and metabolism of other plants that ...co-occur or grow later in the conditioned soil. Plant-soil feedbacks could affect community interactions and dynamics but also be applied in sustainable agriculture to promote plant growth and resistance to pests. In this study, we use a maize companion cropping system, commonly known as “push-pull,” as a model to investigate soil-mediated effects of functional biodiversity, on maize plant growth, and resistance against insect herbivores. We grew maize in soils collected from push-pull (polyculture) and non-push-pull (monoculture) fields. We evaluated maize performance by measuring plant growth, as well as resistance traits (herbivore oviposition and larval feeding, production of defense-related volatile, and non-volatile secondary defense metabolites). Maize plants grown in soil conditioned by push-pull companion cropping had a higher growth rate compared to those grown in soil from non-push-pull monoculture fields. In addition, soil from push-pull fields induced a constitutively higher and qualitatively different emission of volatile organic compounds than soil from non-push-pull fields. Moreover, secondary defense metabolites such as 2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one (DIMBOA), were produced in larger quantities in plants grown in soil from push-pull fields compared to those from monoculture fields. These soil-mediated alterations in plant secondary metabolism were associated with reduced herbivory by larvae of the stemboring pest Chilo partelllus. This study provides novel evidence that plant-soil feedbacks can affect plant metabolism, growth, and resistance to pests. The observed soil-mediated effects on maize plant secondary metabolism can be viewed as emergent properties of plant community composition as well as a potent mechanism of associational resistance. In addition, these soil-conditioning effects provide a novel pest control mechanism of push-pull companion cropping.
Maize, a genetically diverse crop, is the domesticated descendent of its wild ancestor, teosinte. Recently, we have shown that certain maize landraces possess a valuable indirect defense trait not ...present in commercial hybrids. Plants of these landraces release herbivore-induced plant volatiles (HIPVs) that attract both egg
Trichogramma bournieri
Pintureau & Babault (Hymenoptera: Trichogrammatidae) and larval
Cotesia sesamiae
Cameron (Hymenoptera: Braconidae) parasitoids in response to stemborer egg deposition. In this study, we tested whether this trait also exists in the germplasm of wild
Zea
species. Headspace samples were collected from plants exposed to egg deposition by
Chilo partellus
Swinhoe (Lepidoptera: Crambidae) moths and unexposed control plants. Four-arm olfactometer bioassays with parasitic wasps,
T. bournieri
and
C. sesamiae
, indicated that both egg and larval parasitoids preferred HIPVs from plants with eggs in four of the five teosinte species sampled. Headspace samples from oviposited plants released higher amounts of EAG-active compounds such as (
E
)-4,8-dimethyl-1,3,7-nonatriene. In oviposition choice bioassays, plants without eggs were significantly preferred for subsequent oviposition by moths compared to plants with prior oviposition. These results suggest that this induced indirect defence trait is not limited to landraces but occurs in wild
Zea
species and appears to be an ancestral trait. Hence, these species possess a valuable trait that could be introgressed into domesticated maize lines to provide indirect defense mechanisms against stemborers.
False codling moth (FCM) Thaumatotibia leucotreta Meyrick (Lepidoptera: Tortricidae) is currently the main pest of phytosanitary concern in international trade, causing rejection and decline of ...horticultural produce from Kenya exported to the European Union (EU). Overreliance on synthetic insecticides to control this pest is ineffective and unsustainable in the long run, whereas continuous use of pesticides results in high levels of residues in the produce. To gather farmers’ knowledge, attitudes, and practices used by smallholder farmers to manage this pest, a field survey was carried out in 10 Capsicum sp. (Solanales: Solanaceae)-producing counties in Kenya. Data were collected using semi-structured questionnaires administered through face-to-face interviews and focus group discussions involving 108 individual farmers, 20 key informants, and 10 focus group discussions. The majority of the respondents (83.33%) were aware of the FCM infesting Capsicum sp. About three quarters of the farmers (76.85%) reported yield losses and unmarketable quality of FCM-infested Capsicum sp. Most farmers interviewed (99.07%) used insecticides as a management tool. In contrast, only 39.81% of the farmers applied integrated pest management strategies including use of biological control agents and intercropping with repellent plants to control this pest. The results show that FCM is perceived as a significant threat to the horticultural industry of Kenya. Training needs for smallholder farmers and key informants to avoid overreliance on synthetic chemical pesticides and to maintain export goals to the EU where identified.
Plants defend themselves against herbivores through activation of both constitutive and induced defences. Previous studies reported that egg deposition on maize landraces induces the release of ...volatiles that attract parasitoids, but little is known on the effect of these volatiles on subsequent herbivore oviposition. In addition, larval preference and development on these maize landraces is unknown. We evaluated six landraces and one hybrid maize variety for their resistance to Chilo partellus (Swinhoe) (Lepidoptera: Crambidae). Larval orientation, settling, arrest and dispersal, feeding, development, survival, and subsequent oviposition of moths were determined for individuals reared on each of these varieties under laboratory and screen house conditions. For oviposition preference studies, all treatments were initially exposed to egg deposition whereas the control treatments were not. Larval preference was generally higher for hybrid maize, compared to the landraces. Similarly, first‐instar feeding on maize leaves was more intense in hybrid maize than in four of the six landraces. The amount of food consumed and assimilated by third instars over a 24‐h period was, however, not different among the maize varieties. Larval survival was significantly lower in maize landraces (32%) compared to hybrid maize (54%). However, there was no difference in the larval development period between any of the treatments. Two‐choice oviposition assays showed that moths preferred non‐exposed maize landraces for subsequent oviposition, whereas in the hybrid, there was no difference in oviposition preference between exposed and non‐exposed plants. Although the mechanism of larval suppression was beyond the scope of this study, it was inferred that the landraces showed some resistance to C. partellus feeding and that initial egg deposition on these landraces deters further colonisation by the herbivore.
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