ARS | Publication request: The spatial genetic differentiation of the legume pod borer, Maruca vitrata F. (Lepidoptera: Pyralidae) populations in West Africa

Submitted to: Bulletin of Entomological Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 29, 2012
Publication Date: April 17, 2012
Citation: Agunbiade, T.A., Coates, B.S., Kim, K., Forgacs, D., Margam, V.M., Ba, M.N., Binso-Dabire, C.L., Baoua, I., Ishiyaku, M.F., Manuele, T., Pittendrigh, B.R. 2012. The spatial genetic differentiation of the legume pod borer, Maruca vitrata F. (Lepidoptera: Pyralidae) populations in West Africa. Bulletin of Entomological Research. 102(5):589-599.

Interpretive Summary: Larvae that are pests of fruit- and seed-bearing crops threaten producer viability and contribute to human food shortages worldwide. Controlling these pest insects in developing nations and within sub-tropical regions of the United States is difficult due to long crop growing seasons and multiple generations of the pests. Understanding insect pest biology and ecology will help scientists develop ecologically sound methods for managing insect resistance to transgenic crops. This includes cowpea that expresses insecticidal toxins from Bacillus thuringiensis (Bt). We developed molecular genetic markers from polymorphic microsatellite loci within the genome of the legume pod borer. We applied these markers to estimate the level of genetic differences between populations and corroborated prior works that suggested that the population has geographic structuring. These results will be useful to all scientists, particularly in developing countries and sub-tropical regions of the United States who are interested in understanding insect population genetics, and will be useful for developing resistance management strategies prior to the release of transgenic crops for insect pest control.

Technical Abstract: The legume pod borer, Maruca vitrata, is an endemic insect pest that causes significant yield loss to the cowpea crop in West Africa, and contributes to food shortages and malnutrition in native human populations. The genetic structure of Maruca vitrata was investigated among five sites from Burkina Faso, Niger and Nigeria using microsatellite markers. Observed polymorphism ranged from 1 (marker 3393) to 8 (marker 32008) alleles per locus, and observed heterozygosity was from 0.00 to 0.78. Three of the loci deviated significantly from Hardy-Weinberg Equilibrium (HWE) in Nigeria and Burkina Faso, whereas no loci deviated significantly in Niger. Analysis of molecular variance (AMOVA) indicated that 67.35% level of the genetic variation was within individuals compared to 17.28% among populations. A global estimate of subpopulation differentiation (FST) = 0.13 [corrected subpopulation differentiation estimate (FST) = 0.10] was significant (P less than or equal to 0.05) and corroborated by pairwise subpopulation differentiation (FST) values that were significant among all possible comparisons. A significant correlation was predicted between genetic divergence and geographic distance between subpopulations (R-squared = 0.56, P = 0.010), and cluster analysis by the program STRUCTURE predicted that co-ancestry of genotypes were indicative of three distinct populations. The spatial genetic variance among Maruca vitrata in West Africa may be due to limited gene flow, north-south seasonal movement pattern, or other reproductive barriers. This information impacts the current Maruca vitrata cultural, chemical, and biological control strategies, and will help augment current and future cowpea production practices.