Swvey was carried out during 2004 main cropping season to investigate the abundancernand distribution of stemborers, with emphasis on C. partellus in central and easternrnEthiopia. Three species of stemborers, Chilo partellus (Swinhoe), Busseola fusca (Fuller)rnand Sesatnia calamistis (Hampson) were recorded. C. partellus was dominant and widelyrndistributed species recorded in 96 % of the swveyed sites. On the other hand, B. fuscarnwas mainly recorded in highland areas while S. calamistis found at all elevations butrnin small number. Though studies were not conducted so far on the increasing importancernof C. partellus, the current survey revealed the expansion of the pest to high elevatedrnareas as high as 2088 niasl, where it was not recorded earlier in the country.rnObseivations were also made during the survey on the effect of cropping system, wildrnhost and weediness on percent infestation, stemborer composition and density. The resultrnshowed higher level of infestation on monocrops and on fields with wild hosts thanrnintercrop and wild host free fields. Significant variation in level of infestation betweenrncrop types was observed. Chi square test revealed strong relationship between croppingrnsystems, crop type, presence or absence of wild host and species composition atrnintermediate and highland. Borer density was highest at low altitude as compared tornintermediate and high altitude.rnLaboratoiy study was conducted to obseive the combined effect of relative humidity andrntemperature on the biological features of C. partellus. Temperature levels tested werern22Â°C, 26Â°C and 30Â°C while the relative humidity were 40 %, 60 %, and 80 %. The resultrnobtained showed variation on potential and realized fecundity, the developmental time ofrnimmatures, and adult longevity due to differences in temperature levels, relative humidityrnand their interaction. Mean duration of C. partellus life cycle was 70.2 days at 22Â°C andrn80 % relative humidity whereas it took only 26.5 days to complete its life cycle at 30 Â°Crnand 40 % relative humidity. Average life span adult C. partellus ranged 6.9-11.1 days atrn22 Â°C and 2.3 - 7.2 days at 30 Â°Cfor the different levels of relative humidity tested.rnAlthough developmental period of immmatures and adult longevity was longest at lowestrntemperature level, C. partellus successfully completed its life cycle suggesting reason forrnits expansion to high elevated areas.rnKey words: Chilo partellus, infestation, species composition, interactive effect,rndevelopmental time, longevity, fecundity