Abstract:
Rice is the staple food in Sri Lanka. It is estimated that more than 6% of the
harvested paddy is lost due to the damage caused by stored grain pests. Among
these, the rice weevil, Sitophilus oryzae (L) is the most destructive insect pest of
stored rough and milled rice. Although the new trend is to grow indigenous rice
varieties, the traditional rice farmers who grow these varieties face serious
problems in strong rough and milled indigenous rice. The present study was carried
out to find out resistant and susceptible rough and milled stored rice varieties to the
rice weevil S. oryzae under laboratory conditions. Further, density of pest and non
pest groups associated with selected indigenous rice cultivars was also investigated
under the field condition. Damage caused by S. oryzae on six different indigenous
rough rice varieties i.e. Ratdal, Kuruluthuda, Kalu heenati, Hatada vee, Dahanala
and Ma vee and four different indigenous milled rice types i.e. Ratdal,
Kuruluthuda, Kalu heenati and Ma vee were assessed under laboratory conditions
and the density of insect pest groups and non insect pest groups was studied under
the field conditions during the period of February 2008 - October 2008. Basic
information was collected from a questionnaire, through discussions with relevant
officials and field observations. Damage of S. oryzae on six indigenous rough rice
varieties and a hybrid rice variety were evaluated, to find out host resistant and host
susceptible indigenous rice varieties. It was evident that there was a significant
difference between the damage found among indigenous rice varieties (P < 0.001)
and this study also showed that there was a significant difference between adult
mortality in different rough rice varieties ( P < 0.001) tested. Damage done by S.
oryzae on four indigenous milled rice types and a hybrid rice type was also
evaluated in the study. It was evident that there was a significant difference
between emergence of adults in indigenous rice types (P < 0.001). Results also
indicated that there was no significance difference of damage found in indigenous
milled rice varieties. Five indigenous rice varieties and one hybrid variety (Kota
vee) were used in the field experiment. Results indicated that there were significant
difference between mean percentage insects, in vegetative phase of the indigenous
rice varieties (P < 0.005) and ripening phase in indigenous rice varieties (P < 0.05).
Kuruluthuda was identified as partially resistant to Rice weevil (S. oryzae)
compared to hybrid rough rice variety.
