Colonization of resistant and susceptible maize genotypes by the pink stem borer, Sesamia calamistis (Lepidoptera: Noctuidae)

The role of four colonizing responses (oviposition, larval arrest, larval establishment and larval feeding) of Sesamia calamistis (Lepidoptera:Noctuidae) in determining the resistance or susceptibility of eight genotypes of maize Zea mays L.) was elucidated. Four resistant (S59-1, 55 1 1-1, 55 27-1 and 55 27-9, two moderately resistant Tzmi 103 and Tzi 4001), and two susceptible 65 20-2 and Tzmi 407) genotypes were used in the study. S. calamistis exhibited variable colonizing responses on the maize genotypes. The interaction of the responses was also considered in order to estimate the net resistance (determined by low responses reflecting non-preference or antixenosis) or susceptibility (characterized by higher responses that promote colonization) of one genotype in comparison to another. The profiles developed from the study showed that 55 9-1 had five responses in the very low to medium range, thus confirming its resistance to S.calamistis. On the contrary, S5 20-2 had a total of four responses in the medium to very high range, while Tzmi 407 had three responses in the medium to high range and were, therefore, truly susceptible.The profiles of the other genotypes fell between these two extremes.cette 6tude a mis en 6vidence les m6canismes responsables de laresistance et la susceptibilite de huit g€notypes de mais par rapportau comportement de Ponte des femelles, d'orientation (arr€D'd'6tablissement et d'alimentation des larves de Sesomia colomistis.Les trois groupes de g6notypes suivants ont 6t6 6tudi6s: les r€sistants55 9-1, S511-1, 55 27-1 et 55 27-3, les moddrdment resistantsTzmi 103 et Tzi 4001, et les susceptibles 55 2O-2 et Tznni 407. Lar6ponse de l'insecte vis-i-vis d'un genotype 6tait variable selon que telcomportement ou tel autre 6tait concern6. Par ailleurs, la r6ponse del'insecte pour un mdme comportement a vari6 d'un genotype i l'autre.Aussi. les interactions des differentes r€ponses ont-elles 6t6 prises encompte, afin de d6terminer la r6sistance relative (caracterisee par des faibles r6actions qui indiquent la non-preference ou l'antibiose) ou lasusceptibilit6 relative (caract6risde par des fortes rdactions qui facilitentla colonisation) d'un genotype comparativement i un autre. Un profilde l'ensemble des r6actions i chaque gdnotype a ete 6tabli afin depermettre une meilleure comprdhension des diff6rents aspects de cesinteractions. Les diff6rents profiles ont montr6 que 55 9-1 a eu cingrdponses allant de faibles d moyenne, ce qui indique une r€sistancede sa part vis-i-vis de S. calomlsfr. 55 2A-2 au contraire, a eu unerdponse trEs 6lev6e, et trois rdponses moyennes, tarrdis que Tzmi 407en avait deux rdponses moyenne, ce qui les rend trds susceptiblesvis-i-vis de cet insecte. Les profiles des autres g6notypes se trouvaiententre ces deux extrdme

Screening and breeding for resistance to maize stem borers and Eldana in West and Central Africa

Stem borers are one of the major constraints limiting maize productivity in Africa. The most important species reducing maize yield in West and Central Africa are Sesamia calamistis, Eldana saccharina and Busseola fusca. Both the pink stem borer (Sesamia calamistis Walker (Pyralidae) and the sugarcane borer Eldana saccharina Hampson (Noctuidae) infest and reduce maize yields in the lowlands of West and Central Africa. Host pant resistance is very effective in managing the pests and researches conducted in the sub-region have identified promising genotypes with resistance to the two borer species. Such genotypes have been utilised to develop improved varieties with better levels of resistance. Genetic studies revealed that both additive and non-additive gene actions are important in varying degrees for the different components of resistance. The improved varieties are being strategi- cally deployed on-farm while other adapted varieties are being improved for resistance to enhance their usefulness. Progress made in screening and breeding for stem borer resistance in the region is discussed