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 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

Occurrence of Nosema species in honey bee colonies in Kenya

Honey bees (Apis mellifera) provide critical pollination services and livelihood for small-holder farmers in Kenya, thus contributing to nutrition and food security. While honey bee colonies in North America and Europe are in decline due to parasites and pathogens, little is known about the status and effects of the honey bee pathogens and pests on the honey bee populations in Africa. A nationwide survey was conducted in 2012/2013 across eight agro-ecological zones to assess the  presence of Nosema microsporidia and quantify the levels of infection. Nosema microsporidia occurred throughout the eight ecological zones. Infection levels were negatively correlated with altitude, suggesting that environmental factors may play a role in the honey bee host-pathogen interactions. Infections levels were higher in the coastal region than in the interior. There was no evidence of colony size reduction in areas where the Nosema microsporidia was in abundant. The results suggest that Nosema could be an exotic pathogen and may have been recently introduced in Kenya and is spreading to all ecological zones. However, its impact onhoney bee populations is not yet known. This study thus provides baseline data for further detailed survey and analysis of the impact of this pathogen to the Kenyan honey bee colonies with a view of establishing any form of resistance mechanisms of the Kenyan honey bee colonies compared to the European honey bee colonies.Key Words: Honey bee, Nosema, Keny