Variations among the bean pod borer Maruca vitrata (Fabricius Lepidoptera: Crambidae) in the Philippines

The bean podborer Maruca vitrata (Fabricius) is a major insect pest of grain and vegetable legumes. It is now of growing importance in the tropics and temperate regions of the world. It shows a wide host range and geographical distribution indicating the possibility of having variations in Maruca vitrata populations. In this study, the podborers collected from eight bean growing sites in the Philippines from January to December 2002, fed on cowpea, pole sitao, mungbean and snap beans. Most of the sample fed on pole sitao. The genetic variations among populations of the bean podborer M. vitrata sampled from the sites namely: Isabela (San Felipe, Ilagan), Benguet (Tublay and La Trinidad), Nueva Ecija (Valdefuente, Sta. Rosa), Laguna (Tranca, Bay) Palawan (Puerto Princesa), Aklan (Julita, Libacao) and Davao (Pagsabangan, Tagum City) were determined, described and compared. The optimized protocol of Sujin et al.(2002) and Cho(2003) enabled the RNA isolation in M. vitrata. The mitochondrial cytochrome oxidase II (COII) gene from eight M. vitrata populations were sequenced by macrogen, Korea and Michigan State University, USA. The observed sequence divergences of 0.16%-0.83% showed that the seven populations were closely related to each other. They significantly diverged from M. vitrata population sampled from Laguna. The high divergence between Laguna and the other populations is comparable to those between recognized biotypes in other lepidoptera species. The nucleotide composition of the different sequences showed a high A-T content (81%) compared to the C-G ratio, which is typical of other insect species. The results obtained suggest that COII sequence is a suitable basis for inferring phylogenetic relationships in N. vitrata. The restriction enzyme digestion by Msel resulted to a single polymorphic DNA pattern. The polymorphic band with the fragment size of 257 bp was observed in two populations of Benguet, Nueva Ecija, and Isabela but not in Davao and Laguna. There was no DNA pattern observed on the two population from Aklan and Palawan.