Combinations of Leaf Powders of Ruta Graveolens and Azadirachta indica to Enhance the Repellent Activity of Sitophilus zeamais (Motsch.) in Stored Maize in Sri Lanka

Abstract

Attached

M aize w eevil (Sitophilus zeam ais, M o tsch .) is an u tterly u b iquitous and co sm o p o litan field-tostore insect pest w ith an eco n o m ic im p o rtan ce o f stored m aize in tropical and sub-tropical regions o f the w orld. C u rren t ren ew ed interest in rep lacin g the synthetic in secticid es has served as the im petus for the ev alu atio n and in ten sificatio n o f eco -frien d ly an ti-w eev il m easures such as the use o f plant based p o st-h arv est b io-insecticides. T his stu d y w as th erefo re, d esig n ed to investigate the rep ellen t p o ten cy o f th e le a f p o w d ers o f Ruta graveolens and Azadirachta indica individually and in co m b in atio n s o f v ario u s pro p o rtio n s u n d er am b ien t lab o rato ry conditions against Sitophilus zeam ais in b o th co n tact and v ap o u r form s. F o r b o th p lan ts, 50 g each o f m aize grains w ere m ix ed w ith le a f p o w d ers at d ifferen t doses o f 1.0, 3.0, 5.0, 7.0 and 10.0 g and the repellent rate w as reco rd ed w ithin an h o u r o f w eevil introduction. T h e rep ellen t potency o f three com bination ratio s o f 1:1, 1:2 and 2:1 o f R. graveolens and A. indica le a f pow ders incorporating into the d osage level o f 10.0 g w as evaluated at ev ery 10 m in u te intervals up to an hour o f w eevil exposure. T h e h ig h est contact rep ellen t effect o f le a f p o w d ers w as p roduced by R. graveolens (9 7 ± 2 .7 4 % ) fo llo w ed b y A. indica (74 ± 5 .4 8 % ) w h ereas h ig h est fum igation repellent effect o f le a f p o w d ers w as ex h ib itin g by R. graveolens (9 6 ± 2 .2 4 % ) follow ed again by A. indica (4 7 ± 2 .7 4 % ) at the h ig h est d osage o f 10.0 g w ithin an h o u r o f w eevil exposure w hen th ey w ere tested individually. A ll co m b in atio n s repelled S. zeam ais ad u lts at a faster rate than w hen eith er p o w d er w as tested in d iv id u ally w h ilst the 2:1 co m b in atio n o f R. graveolens and A. indica ex h ib itin g the h ig h est rep ellen t rates o f 100% and 9 8 % in b o th co n tact and v apor form s resp ectiv ely w ithin 50 m in u tes o f post treatm en t thus in creasin g the rep ellen t potential o f the respective le a f p o w d ers to a great extent. T he le a f p o w d ers o f the tw o p lants under present in vestigation rev ealed th eir im proved grain p ro tectin g cap ab ility w hen used individually an d in m ix tu res to be u sed as bio -ratio n al and natural leads in large-scale p rotection o f stored m aize.