QTL Mapping of Traits Associated with Dual Resistance to the African Stem Borer (Busseola fusca) and Spotted Stem Borer (Chilo partellus) in Sorghum (Sorghum bicolor)

Sorghum (Sorghum bicolor (L.) Moench) is an important food crop in semi-arid tropics. The crop grain yield ranges from 0.5 t/ha to 0.8 t/ha compared to potential yields of 10 t/ha. The African stem borer Busseola fusca Fuller (Noctuidae) and the spotted stem borer Chilo partellus Swinhoe (Crambidae), are among the most economically important insect pests of sorghum. The two borers can cause 15% - 80% grain yield loss in sorghum. Mapping of QTLs associated with resistance traits to the two stem borers is important towards marker-assisted breeding. The objective of this study was to map QTLs associated with resistance traits to B. fusca and C. partellus in sorghum. 243 F9:10 sorghum RILs derived from ICSV 745 (S) and PB 15520-1 (R) were selected for the study with 4,955 SNP markers. The RILs were evaluated in three sites. Data was collected on leaf feeding, deadheart, exit holes, stem tunnels, leaf toughness, seedling vigour, bloom waxiness, and leaf glossiness. ANOVA for all the traits was done using Genstat statistical software. Insect damage traits and morphological traits were correlated using Pearson’s correlation coefficients. Genetic mapping was done using JoinMap 4 software, while QTL analysis was done using PLABQTL software. A likelihood odds ratio (LOD) score of 3.0 was used to declare linkage. Joint analyses across borer species and sites revealed 4 QTLs controlling deadheart formation; 6 controlling leaf feeding damage; 5 controlling exit holes and stem tunneling damages; 2 controlling bloom waxiness, leaf glossiness, and seedling vigour; 4 conditioning trichome density; and 6 conditioning leaf toughness. Joint analyses for B. fusca and C. partellus further revealed that marker CS132-2 colocalised for leaf toughness and stem tunneling traits on QTLs 1 and 2, respectively; thus, the two traits can be improved using the same linked marker. This study recommended further studies to identify gene(s) underlying the mapped QTLs.

A system dynamics model for pests and natural enemies interactions

Stemborers (Busseola fusca, Sesamia calamistis and Chilo partellus), the fall armyworm (Spodoptera frugiperda) and associated parasitoids constitute an interacting system in maize fields in Kenya. This work aims at developing and evaluating models that represent the evolution of those interactions by applying system thinking and system dynamics approaches with its archetypes [causal loop diagram (CLD), reinforcing (R) and balancing (B)] to analyse the population of these multi-species systems. The software Vensim PLE 8.0.9 was used to implement the models and carry out the simulations of single- and multi-species systems. The results showed that when a single pest species with its associated parasitoids interact with the host plant, the species was able to establish and sustain by cyclical relationship between populations of the pest and the associated parasitoids. However, in multi- pest species systems, dominance of S. frugiperda and C. partellus over B. fusca and S. calamistis was observed, but without extinction. However, there was a likelihood for B. fusca being displaced by C. partellus. Overall, the models predict the co-existence of fall armyworm with stemborer species as an additional pest of maize in Africa that need to be considered henceforth in designing IPM strategies in maize.

Comprehensive Transcriptome of the Maize Stalk Borer, Busseola fusca, from Multiple Tissue Types, Developmental Stages, and Parasitoid Wasp Exposures

Busseola fusca (Fuller) (Lepidoptera: Noctuidae), the maize stalk borer, is a widespread crop pest in sub-Saharan Africa that has been the focus of biological research and intensive management strategies. Here, we present a comprehensive annotated transcriptome of B. fusca (originally collected in the Western Province of Kenya) based on ten pooled libraries including a wide array of developmental stages, tissue types, and exposures to parasitoid wasps. Parasitoid wasps have been used as a form of biocontrol to try and reduce crop losses with variable success, in part due to differential infectivities and immune responses among wasps and hosts. We identified a number of loci of interest for pest management, including genes potentially involved in chemoreception, immunity, and response to insecticides. The comprehensive sampling design used expands our current understanding of the transcriptome of this species and deepens the list of potential target genes for future crop loss mitigation, in addition to highlighting candidate loci for differential expression and functional genetic analyses in this important pest species.

Biocidal Activities of Seed Oils of Jatropha curcas and Moringa oleifera on Development of African Maize Stalk borer, Busseola fusca Fuller (Lepdoptera: Pyralidae)

Laboratory experiment was conducted at the Department of Crop Protection Laboratory, Faculty of Agriculture, Bayero University, Kano, in order to assess the effect of oils obtained from the seeds of Jatropha curcas and Moringa oleifera on African Maize Stalk Borer (Busseola fusca Fuller). The effects of the plant seed oils on larvae mortality, pupae and adult emergence were tested on freshly cut leaves/stem of maize 3-4 cm long) and treated with the prepared plant oils at various concentrations (10, 20, and 30%) and control (0%). The experiment was laid out in a completely randomized design and replicated four times. The results showed that both plant seeds oils were lethal to the developmental stages of B. fusca, causing mortality (21%) to the larvae, and subsequently preventing and/or suppressing pupae (2.08) and adult emergence (1.95). Treatment at 30% concentration was found to be more lethal to all the developmental stages of the test insect. Based on the findings of this study, it is recommended that any of the plant seed oils at 30 % concentration could be used to manage B. fusca.