Laboratory Evaluation of Some Indigenous Plant Extracts Against Granary Weevil, Sitophilus granarius L. (Coleoptera:Curculionidae)

MATERIALS AND METHODS

An experiment was carried out in the laboratory of the Department of Entomology, Bangladesh Agricultural University (BAU), Mymensingh during the period from April 2000 to February, 2001. Sitophilus granarius were obtained from a laboratory culture maintained at 27±3^OC and 70-75% relative humidity. Urmoi, available only in the coastal region of Bangladesh was collected from the district of Patuakhali and the rest of the three plants were collected from different places of BAU campus, Mymensingh. The fine and uniform dusts were prepared by pulverizing the dried leaves and seeds/bark (bark extract, instead of seed, was used in case of mehedi) with the help of grinder. Plant extracts were prepared by evaporating the filtrates of stirred mixture of dusts and solvents (acetone, ethanol, methanol and water were used as solvents). Four different concentrations 2.5, 5.0, 7.5 and 10.0% (v/v) of each plant extract were prepared with the respective solvents.

Growth inhibition test: The rearing media (wheat) were treated with different plant extracts at doses of 2.5, 5.0, 7.5 and 10.0%. Different petri dishes were filled up with treated and untreated (control) food (10 g/petridish). Five pairs of newly emerged adult insects were released in each pot at 7, 14 and 21 days after treatment (DAT). Three replications were made for each dose. All the pots were kept in the growth chamber at 27-33^OC and 70-75% RH. The adult insects from each petridish were removed after 7 days of releasing insects for each treatment. On subsequent days the number of adults emerged per day from each petridish were recorded from 30 to 42 days after setup. Then the inhibition rate (IR%) was calculated by the formula of Talukder and Howse (1994).

Grain protection efficacy test: Different leaf, seed/bark extracts of urmoi, karanja, bitter gourd and mehedi were mixed with the rearing media (wheat) at he doses of 2.5, 5.0, 7.5 and 10.0%. Petri dishes were filled with treated and untreated food. Three replications were made for each dose. Petri dishes containing 70 g of wheat and extracts mixture were shaken manually to ensure uniform coating or uniform distribution of extracts on the grains. Petri dishes were arranged in the laboratory following the completely randomized design (CRD). Then the number of insects in each petridish was counted at 5 days interval up to 30 days.

Seed viability test: Wheat seeds of the variety 'Sonalika' popular at farmer's level, were collected from Wheat Research Centre (WRC), Bangladesh Agricultural Research Institute. Wheat for seed purpose was treated with different plant extracts at the doses of 2.5, 5.0, 7.5 and 10.0% and preserved for three months. Control was maintained by taking only solvent with no extract. The seeds were taken to test their viability. Fifty seeds for each treatment were placed on petri dishes (90 mm diameter) containing water soaked blotting paper. The well germinating seeds were counted in all petri dishes after 7 days of setting and the data were recorded. Each dose of individual extract was replicated three times. The petri dishes containing treated and untreated (control) grains were arranged in completely randomized design (CRD). The mean values were separated by Duncan's multiple range test (DMRT) (Duncan, 1957).

RESULTS AND DISCUSSION

Growth inhibition effect: It was found that all the treated plant extracts reduced the progeny adult emergence of S. granarius in comparison to control and the effects, in general, was done dependent.

Table 1:	Adult emergence and inhibition rate of granary weevil, S. granarius treated with extracts of different plants at different DAT

Table 2:	Adult emergence and inhibition rate of granary weevil, treated with leaf and seed/bark extracts of different plants at different DAT (Interaction of plant and plant parts)

Table 3:	Adult emergence and inhibition rate of granary weevil, treated with leaf and seed/bark extracts of different solvents at different DAT (Interaction of plant and plant parts)

Table 4:	Adult emergence and inhibition rate of granary weevil, treated with leaf and seed/bark extracts of different solvents at different DAT (Interaction of plant and plant parts)

Table 5:	Protectant effect of different plant extracts on granary weevil, at different DAT

Table 6:	Protectant effect of extracts of different plant parts on granary weevil S. granarius at different DAT (Interaction of plant and plant parts)

Table 7:	Protectant effect of extracts at different doses on granary weevil S. granarius at different DAT (Interaction of plant and plant parts).

Table 8:	Germination rate of wheat seeds treated with extracts of different plants at different doses (Interaction of plant and dose)

Table 9:	Germination rate of wheat seed treated with different plant extracts of different solvents (Interaction of plant and solvent)
Within column values followed by different letter(s) are significantly different by DMRT at p<0.05. S = Standard error.

The reduction of adults (inhibition rate) was the highest in urmoi (53.53%) followed by karanja (48.07%), bitter gourd (47.81%) and mehedi (40.52%) at 7 DAT. Almost similar trend was observed in 14 and 21 DAT (Table 1). There was a significant difference between leaf and seed/bark extract at 7, 14 and 21 DAT (Table 2). Performance of seed extracts was observed better than that of leaf extracts. Different solvents also possessed significant influence on the number of adult emergence and IR% at 7 and 14 DAT (Table 3). Number of adults emerged was inversely and inhibition rate was directly proportional to doses (Table 4). In almost all cases highest number of adults was emerged from untreated grain.

Shelke et al. (1985) found to afford 91.96-100% oviposition deterrence of karanja oil against Aulocophora foveicollis. Babu et al. (1989) observed karanja oil to reduce oviposition of bruchics over 18 months of storage. Khaire et al. (1992) adult emergence of pigeon peas was prevented by karanja for up to 100 days. Doharey (1983) found that Dacus cucurbitae preferred bitter gourd among pumpkin, bitter gourd and squash gourd. The life cycle was shorter on it than the others.

Here it is found from previous studies that efficacy of the same plant varied in different insect. So the result of the present study, may be justifiable.

Grain protection effect: The efficacy of bitter gourd, karanja, mehedi and urmoi leaf and seed/bark extract as protectants for wheat against granary weevil was evaluated by comparing the number of insects found in treated grains. All the plant extracts effectively protect wheat grain from granary weevil up to 5 DAT. Infestation started from 10 DAT and the infestation was found very high up to 30 DAT for all the plant extracts. The mean highest number of insects (2.34) was observed in bitter gourd treated seed and the lowest (2.02) in urmoi treated seed (Table 5). The persistent effect of all the four plant leaf and seed/bark extracts is more or less same (Table 6). Dose had slight influence on persistent effect (Table 7). The highest number of insects was always recorded in untreated grain. Number of insects increased with the increase in days.

Sangappa (1977) reported that karanja could be effective in checking the infestation of Callosobruchus chinensis in red gram. Sighamony et al. (1986) found to have provided good protecting action of karanja against the S. oryzae for up to 60 days of exposure.

Effect on germination: Always highest percentage of seed germination was recorded in control treatment. Germination percentage of wheat seeds decreased gradually with the increase in doses (Tables 8, 9, 10 & 11). The present findings are in agreement with the view of Singh et al. (1987), Sighamony et al. (1986) and Kalinovic et al. (1997), who reported that seeds treated with plant materials did not adversely affect the seed germination.

Table 10:	Germination rate of wheat seeds treated with plant extracts of different solvents at different doses (Interaction of solvent and dose)

Table 11:	Germination rate of wheat seeds treated with extracts of different plant parts at different doses (Interaction of plant part and dose)
DAT= Days after treatment. Within column values followed by different letter(s) are significantly different by DMRT at p<0.05.S = Standard error.

Low cost technique of extraction: Four types of extract e.g, acetone, ethanol, methanol and water were used. It was observed that ethanol extract of plants were more efficient than that of other extracts. The efficiency of acetone and water extracts was more or less similar. Researchers can use ethanol extract though its cost is high. On the other hand, our farmers are faced with the high costs of insecticides. Most of them can no longer afford synthetic insecticides to protect the stored products. So, farmers can use water extract because they require less money to prepare extracts in comparison with ethanol extracts.

Efficacy of different plant extracts was evaluated for their growth inhibiting and grain protecting action against rice weevil. Effect on germination of wheat seed and low cost technique of extraction was also evaluated. The extracts could protect the adult emergence for up to 21 days. Protecting action was found up to 30 days but at that time it was very low. Considering the cost of extraction water is recommended for farmer use.