Browsing by Author "John Colvin"

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Bean Leaf Beetle (Ootheca spp.) (Coleoptera: Chrysomelidae) Management via Planting Timing and Insecticides
(Insects, 2022-08-07) Charles Halerimana; Samuel Kyamanywa; Samuel Olaboro; Pamela Paparu; Stanley T. Nkalubo; John Colvin; Robert A. Cheke; Darren J. Kriticos; Michael H. Otim
Bean leaf beetles (Ootheca spp.) (Coleoptera: Chrysomelidae) are one of Africa’s most important pests of the common bean (Phaseolus vulgaris L.). Roots, leaves, floral parts, and young pods are all attacked, leading to a considerable loss in grain yield. In Uganda, there are no comprehensive prescribed management strategies for bean leaf beetles, but farmers typically try to control the pest by delaying bean crop sowing, and to a lesser extent, using insecticides. Although farmers have consistently implemented the two approaches, there is no information on the effects of the approaches in Uganda. To assess the impact of planting timing and insecticide spray regimes on bean leaf beetle populations, concomitant foliar damage, and grain yield, we set up trials in three agro-ecological zones with known presence of the beetles during the second rainy season of 2016 (2016) and the first rainy season of 2017 (2017). The first planting, coinciding with early planting, was conducted within one week after the onset of rains. The second planting, coinciding with mid planting, followed two weeks later, while the third planting, considered late planting in this study, was conducted one month after the second planting. A foliar application of cypermethrin commencing at 7 days after emergence (DAE), 14 DAE, 21 DAE, 28 DAE, and 35 DAE; a soil drench of imidacloprid at planting combined with a foliar spray starting at 7 DAE; and an untreated control were among the insecticide spray regimes evaluated. Higher bean leaf beetle abundance was recorded from mid-planting, while higher foliar damage was recorded from late planting in two of the three agro-ecological zones. However, higher marketable grain yield was recorded from early planting in all agro-ecological zones, suggesting that delayed planting may not be beneficial. Insecticide application reduced foliar damage and increased marketable grain yield, with a combination of soil drench and foliar spray resulting in much less foliar damage and, as a result, higher grain yield. However, this did not result in economic benefits. Furthermore, marketable grain yield was higher when insecticide spray regimes were combined with early planting in all agro-ecological zones during both seasons. Our findings suggest that the common bean should be planted early and that the control of the bean leaf beetle should target both the adults and the juvenile stages in the soil. Therefore, there is a need for farmers to be able to access less-expensive soil treatments.
Comparative evolutionary analyses of eight whitefly Bemisia tabaci sensu lato genomes: cryptic species, agricultural pests and plant-virus vectors
(BMC Genomics, 2023-07-19) Lahcen I. Campbell; Joachim Nwezeobi; Sharon L. van Brunschot; Tadeo Kaweesi; Susan E. Seal; Rekha A. R. Swamy; Annet Namuddu; Gareth L. Maslen; Habibu Mugerwa; Irina M. Armean; Leanne Haggerty; Fergal J. Martin; Osnat Malka; Diego Santos‐Garcia; Ksenia Juravel; Shai Morin; Michael E. Stephens; Paul Visendi Muhindira; Paul J. Kersey; M. N. Maruthi; Christopher A. Omongo; Jesús Navas‐Castillo; Elvira Fiallo‐Olivé; Ibrahim Umar Mohammed; Hua‐Ling Wang; Joseph Onyeka; Titus Alicai; John Colvin
Background The group of > 40 cryptic white y species called Bemisia tabaci sensu lato are amongst the world’s worst agricultural pests and plant‐virus vectors. Outbreaks of B. tabaci s.l. and the associated plant‐virus diseases continue to contribute to global food insecurity and social instability, particularly in sub‐Saharan Africa and Asia. Published B. tabaci s.l. genomes have limited use for studying African cassava B. tabaci SSA1 species, due to the high genetic divergences between them. Genomic annotations presented here were performed using the ‘Ensembl gene annotation system’, to ensure that comparative analyses and conclusions reflect biological differences, as opposed to arising from different methodologies underpinning transcript model identification. Results WepresentheresixnewB.tabacis.l.genomesfromAfricaandAsia,andtwore‐annotatedpreviously published genomes, to provide evolutionary insights into these globally distributed pests. Genome sizes ranged between 616—658 Mb and exhibited some of the highest coverage of transposable elements reported within Arthropoda. Many fewer total protein coding genes (PCG) were recovered compared to the previously published B. tabaci s.l. genomes and structural annotations generated via the uniform methodology strongly supported a repertoire of between 12.8—13.2 × 103 PCG. An integrative systematics approach incorporating phylogenomic analysis of nuclear and mitochondrial markers supported a monophyletic Aleyrodidae and the basal positioning of B. tabaci Uganda‐1 to the sub‐Saharan group of species. Reciprocal cross‐mating data and the co‐cladogenesis pattern of the primary obligate endosymbiont ‘Candidatus Portiera aleyrodidarum’ from 11 Bemisia genomes further supported the phylogenetic reconstruction to show that African cassava B. tabaci populations consist of just three biological species. We include comparative analyses of gene families related to detoxification, sugar metabolism, vector competency and evaluate the presence and function of horizontally transferred genes, essential for understanding the evolution and unique biology of constituent B. tabaci. s.l species. Conclusions These genomic resources have provided new and critical insights into the genetics underlying B. tabaci s.l. biology. They also provide a rich foundation for post‐genomic research, including the selection of candidate gene‐ targets for innovative white y and virus‐control strategies.
Impacts of cassava whitefly pests on the productivity of East and Central African smallholder farmers
(Journal of development and Agricultural Economics, 2022-09-09) Paul Mwebaze; Sarina Macfadyen; Paul De Barro; Anton Bua; Andrew Kalyebi; Fred Tairo; Donald Kachigamba; Christopher Omongo; John Colvin
A key constraint to smallholder cassava production systems in Africa is the cassava whitefly pest species. These pests are a group of several cryptic species within Bemisia tabaci that cause direct damage to cassava and vector viruses that cause disease. We employ a farm-level stochastic production frontier (SPF) model to determine the impacts of the cassava whitefly pests on the productivity and technical efficiency (TE) of smallholder cassava farmers in Malawi, Tanzania, and Uganda. Primary data were collected from a sample of cassava farmers using a structured survey questionnaire. A total of 1200 farmers were selected from Malawi (400), Tanzania (350) and Uganda (450), and interviewed using a multi-stage sampling technique. Cassava output was significantly correlated with land area, the quantity of cuttings used to propagate the crop, and total labor used. We found that whitefly infestations as well as several socio-economic factors significantly affected the technical inefficiency of cassava farmers. Whitefly and disease infestations contributed to higher levels of technical inefficiency of cassava farmers. The mean TE score was significantly lower (50%) for cassava farms with whitefly infestation compared to those without any infestation (80%). These findings underscore the need for policies to ensure that cassava farmers have better access to improved inputs, especially clean planting materials, and the knowledge to integrate this technology into their farming system effectively.
In silico prediction of candidate gene targets for the management of African cassava whitefly (Bemisia tabaci, SSA1-SG1), a key vector of viruses causing cassava brown streak disease
(PeerJ, 2024-02-23) Tadeo Kaweesi; John Colvin; Lahcen Campbell; Paul Visendi; Gareth Maslen; Titus Alicai; Susan Seal
Whiteflies (Bemisia tabaci sensu lato) have a wide host range and are globally important agricultural pests. In Sub-Saharan Africa, they vector viruses that cause two ongoing disease epidemics: cassava brown streak disease and cassava mosaic virus disease. These two diseases threaten food security for more than 800 million people in Sub-Saharan Africa. Efforts are ongoing to identify target genes for the development of novel management options against the whitefly populations that vector these devastating viral diseases affecting cassava production in Sub-Saharan Africa. This study aimed to identify genes that mediate osmoregulation and symbiosis functions within cassava whitefly gut and bacteriocytes and evaluate their potential as key gene targets for novel whitefly control strategies. The gene expression profiles of dissected guts, bacteriocytes and whole bodies were compared by RNAseq analysis to identify genes with significantly enriched expression in the gut and bacteriocytes. Phylogenetic analyses identified three candidate osmoregulation gene targets: two a-glucosidases, SUC 1 and SUC 2 with predicted function in sugar transformations that reduce osmotic pressure in the gut; and a water-specific aquaporin (AQP1) mediating water cycling from the distal to the proximal end of the gut. Expression of the genes in the gut was enriched 23.67-, 26.54- and 22.30-fold, respectively. Genome-wide metabolic reconstruction coupled with constraint-based modeling revealed four genes (argH, lysA, BCAT & dapB) within the bacteriocytes as potential targets for the management of cassava whiteflies. These genes were selected based on their role and essentiality within the different essential amino acid biosynthesis pathways. A demonstration of candidate osmoregulation and symbiosis gene targets in other species of the Bemisia tabaci species complex that are orthologs of the empirically validated osmoregulation genes highlights the latter as promising gene targets for the control of cassava whitefly pests by in planta RNA interference.
Spatio-temporal changes in endosymbiont diversity and composition in the African cassava white y, Bemisia tabaci SSA1
(Frontiers, 2022-11-18) Hajar El Hamss; M. N. Maruthi; Hadija M. Ally; Christopher A. Omongo; Hua-Ling Wang; Sharon van Brunschot; John Colvin; Hélène Delatte
Sap-sucking insects, including whiteflies, are amongst the most devastating and widely distributed organisms on the planet. They are often highly invasive and endosymbiont communities within these insects help them adapt to new or changing environments. Bemisia tabaci (Gennadius; Hemiptera: Aleyrodidae) white y species are vectors of more than 500 known plant- viruses and harbour highly diverse endosymbionts communities. To date, however, white y–endosymbiont interactions, community structure and their spatio-temporal changes are still poorly understood. In this study, we investigated the spatio-temporal changes in the composition and diversity of bacterial endosymbionts in the agricultural crop pest white y species, Bemisia tabaci sub-Saharan Africa 1-subgroup 1 and 2 (SSA1-SG1 and SSA1- SG2). 16S rRNA amplicon sequencing analysis was carried out to characterise endosymbiont compositionsin eld-collected SSA1 (SSA1-SG1 and SSA1- SG2) populations infesting cassava in Uganda in 1997 and 2017. We detected Portiera, Arsenophonus, Wolbachia, Hamiltonella and Hemipteriphilus, with Arsenophonus and Wolbachia infections being predominant. Hemipteriphilus and Hamiltonella frequencies were very low and were detected in seven and two samples, respectively. Bacterial diversity based on three independent parameters including Simpson index, number of haplotypes and Bray–Curtis dissimilarity matrix was significantly higher in 1997 than in 2017. This period also coincided with the advent of super-abundant cassava-white y populations on cassava crops in Uganda. We discuss how endosymbionts may influence the biology and behaviour of whiteflies leading to population explosions.