MSc

The study entitled “Management of beetle pests in stored rice using
botanicals” was carried out at the Department of Agricultural Entomology, College
of Agriculture, Vellayani, during 2016-2018. The objectives of the study was to
document major beetle pests of stored rice in Thiruvananthapuram district and to
develop effective management measures using botanicals.
The occurrence of beetle pests of stored rice in ration shops and retail
provision stores in Thiruvananthapuram district of Kerala was examined through a
preliminary survey. Effective management measures using botanicals were tested
against one major beetle pest identified from survey. Three experiments were
conducted using plant extract, dried plant parts and essential volatile oils for the
management of the major beetle pest.
As per the results of survey, out of 25 rice samples 23 were contaminated
with rice weevil Sitophilus oryzae L. with a mean number of 14.68 in 100 g rice
followed by saw toothed grain beetle. In the light of above, further studies were
undertaken to manage rice weevil using botanicals. Experiment with extract of plant
parts viz., tulsi leaves (Ocimum tenuiflorum L.), neem leaves (Azadirachta indica
A.Juss.), garlic bulblets (Allium sativum L.), bird chilli fruits (Capsicum frutescens
L.), mint leaves (Mentha arvensis L.) and pepper seeds (Piper nigrum L.) at two
concentrations (5 and 10%) (w/v) were conducted. The highest percentage mortality
was recorded in treatment with garlic bulb 10 % (53.33) which was on par with
garlic bulb 5 % (38.33), tulsi leaves 10 % (38.33) and bird chilli fruit 10% (36.67).
The treatment with tulsi leaves 10 % recorded maximum repellent effect of 40.00
per cent which was on par with pepper seed 10 % (38.33), mint leaves 10 % (26.67)
and bird chilli fruit 10 % (23.33). While examining both mortality and repellent
effect of plant extract, treatment with tulsi leaves 10 % showed the highest reduction
(78.33) of weevils with decreased progeny emergence and grain damage.
Management of beetle pest using dried plant parts viz. tulsi leaves
(O. tenuiflorum), neem leaves (A. indica), clove flower buds (Syzygium aromaticum
(L.)), nutmeg mace (Myristica fragrans Houtt.), mint leaves (M. arvensis) and curry
leaves (Murraya koenigii (L.)) at two concentrations (2 and 4%) (w/w) showed that
mint leaves 4 % was the most effective treatment with 56.67 per cent mortality
which was on par with nutmeg mace 4 % (35.00). The highest percentage repellency
of weevils was recorded in rice treated with nutmeg mace 4 %, (31.67) and the
lowest progeny emergence and grain damage also. However considering both
mortality and repellent effect of dried plants parts, treatment with mint leaves 4 %
showed the highest reduction of weevils.
Effect of essential volatile oils on mortality of beetles were carried with four
oils viz., clove (S. aromaticum), cinnamon (Cinnamomum zeylanicum Blume),
lemon grass (Cymbopogon flexuosus (Nees ex steud)) and pepper (P. nigrum).
Preliminary toxicity bioassays (without food and with food) were carried for fixing
the concentrations of these oils. Percentage mortality of weevils by volatile
essential oils increased with increase in concentration and period of exposure.
Pepper oil 200 μl 500 cm-3 caused cent per cent mortality without any progeny
emergence whereas cinnamon oil 30 μl 500 cm-3 caused 95.55 per cent mortality of
weevils.
The rice weevil S. oryzae was found to be the major beetle pest associated
with stored rice. Among the plant extracts, treatment with tulsi leaves 10 % showed
the highest reduction of weevils with decreased progeny emergence and grain
damage. Treatment with dried plant parts revealed that mint leaves (4 %) showed
the highest reduction of weevils whereas the lowest progeny emergence and grain
damage were observed in treatment with dried nutmeg mace 4 %. Among the
essential volatile oils pepper oil 200 μl 500 cm-3 caused cent per cent mortality of
rice weevil at four days after treatment without any progeny emergence.