The Relationship between Grassland Composition on Stemborer Abundance on Grasses Surrounding Maize Farms

Grasslands are known to host crop pests and may act as the reservoir of pests affecting maize production. This research aimed at determining the effect of grassland composition on abundance of stemborers on grasses sorrouding maize farms in western Kenya. The experimental set up followed a complete random block design (CRBD); with four elevations at Lambwe, Homabay, Luanda and Mt. Elgon assigned as blocks based on different altitudes. Sampling was done in two seasons, during the short rain season of 2019 and the long rain season of 2020. Grasslands surrounding four pairs of push-pull and non-push-pull maize farms were assessed. Data on grass species diversity and the corresponding number of stemborers were collected from five quadrates per transect of 500m, for 4 transects per farm. The four transects originated from the midpoint of push-pull and non-push pull maize farm. A mixed design analysis of variance was used to test for variance within the elevation’s variability. The most common types of grasses surrounding most of the maize farms were mainly Cynadon dactylon and Immensis spp. These results point at the role of grasslands surrounding maize farms as reservoirs for the stem borers which need to be managed to reduce stem borer and fall armyworm infestations in the surrounding maize farms

An indirect defence trait mediated through egg-induced maize volatiles from neighbouring plants

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 fourarm 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

Responses of parasitoids to volatiles induced by Chilo partellus oviposition on teosinte, a wild ancestor of maize

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

Fig. 1 in Notes on the Natural History of Phoxomeloides gedyeiSchein (Coleoptera: Scarabaeidae) in Kenya

Fig. 1. Map of Kenya showing sites where honey bee colonies were surveyed from 2007–2012. The square represents the location of Katolongwe, where Phoxomeloides gedyei was observed, and the black dots are surveyed locations where it was absent.Published as part of <i>Mutyambai, Daniel M., Mutunga, Jacqueline M. & Fombong, Ayuka T., 2015, Notes on the Natural History of Phoxomeloides gedyeiSchein (Coleoptera: Scarabaeidae) in Kenya, pp. 504-506 in The Coleopterists Bulletin 69 (3)</i> on page 504, DOI: 10.1649/0010-065x-69.3.504, <a href="http://zenodo.org/record/10113968">http://zenodo.org/record/10113968</a&gt

Responses of parasitoids to volatiles induced by Chilo partellus Oviposition on Teosinte, a wild ancestor of maize

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 stemborer

Volatile emission (ng/plant/hr) (mean ± s.e) from egg exposed (inducing), neighbouring (induced) and control maize plants (N = 5).

<p>Volatile emission (ng/plant/hr) (mean ± s.e) from egg exposed (inducing), neighbouring (induced) and control maize plants (N = 5).</p

Behavioural response of parasitoids to volatiles collected from a hybrid, HB515, neighbouring induced maize plant (exposed to maize plant emitting egg-induced volatiles) and an unexposed control plant in a four-arm olfactometer bioassay.

<p>Response of (<b>A</b>) <i>Trichogramma bournieri</i>; (<b>B</b>) <i>Cotesia sesamiae</i>. Bars marked by same letters within a graph are not statistically different (<i>P</i>>0.05).</p

Behavioural response of parasitoids to volatiles collected from a landrace, ‘Nyamula’, neighbouring induced maize plant (exposed to maize plant emitting egg-induced volatiles) and an unexposed control plant in a four-arm olfactometer bioassay.

<p>Response of (<b>A</b>) <i>Trichogramma bournieri</i>; (<b>B</b>) <i>Cotesia sesamiae</i>. Bars marked by different letters within a graph are statistically different (<i>P</i><0.05).</p

Behavioural response of female parasitoids to volatiles collected from landrace maize seedlings, ‘Nyamula’ with or without <i>Chilo partellus</i> eggs in a four-arm olfactometer bioassay.

<p>Response of (<b>A</b>) <i>Trichogramma bournieri</i>; (<b>B</b>) <i>Cotesia sesamiae</i>. Bars marked by different letters within a graph are statistically different (<i>P</i><0.05).</p