Abstract
The insecticidal activities of methanolic extracts of two weedy plants leaves Bidens pilosa L. and Rumex dentatus L. at three different concentrations 3, 5 and 7% were tested against three stored grain pests, Rice weevil Sitophilus oryzae L. Saw-toothed grain beetle Oryzaephilus surinamensis L., and Bean weevil Acanthoscelides obtectus Say, compared to Neem oil as a commercial product at the same concentrations for exposure periods 24, 48, 72 and 96 hrs of treatment under laboratory conditions. Results revealed that different concentrations and exposure periods of the two extracts and Neem oil had significant lethal effects against these tested grain pests. In general, R. dentatus extract was found to be the most toxic against the tested grain pests and caused the highest mortality (100.00%) for the three pests S. oryzae, O. surinamensis and A. obtectus when applied at its highest concentration (7%) for an exposure time of 96 hrs (the highest time), followed by Neem oil 90.0±10.0, 70.00±13.3 and 90.00±2.8%, then B. pilosa extract 75.83±5.8, 79.33±5.46 and 87.50±7.2%, respectively at the same concentration and exposure time, indicating that the obtained mortality percentages were concentration and exposure time-dependent. Finally, these results demonstrate that, R. dentatus extract can be used as a promising pesticide against the three stored products insect pests investigated under this study, and strongly recommended to be used as stored grain protectants in the future.
Highlights
The group of insect species associated with postharvest products is commonly called stored product pests
The insecticidal effects resulted from R. dentatus extract, B. pilosa extract and Neem oil, applied at different concentrations and exposure periods, on the adults of O. surinamensis, S. oryzae and A. obtectus are given in Tables (1,2 &3) and Figs. (1, 2 and 3)
Insecticidal Effect of Plant Essential Oils Against O. surinmensis: The obtained data of the mean mortality of R. dentatus extract, B. pilosa extract and Neem oil against O. surinmensis adult showed in Table 1 and Figure 1 revealed that R. dentatus was the most effective that exhibit maximum mortality (100.00%) with its highest concentration (7%) after 96hrs of exposure; while B. pilosa and Neem oil-induced their highest mortality of 79.33±5.46 and 70.00±13.3% respectively with the same concentration and exposure time
Summary
The group of insect species associated with postharvest products is commonly called stored product pests. The main damage and product loss of these stored pests are caused by feeding and contamination by insects themselves or their cast skins and immature stages of the pupa They can cause reductions in weight, quality, commercial value and seed viability. These insects can cause losses of 9-10 % in developing countries while, the losses can be more than 50 % in undeveloped countries (Pimentel, 1991) and (Wolpert, 1967) The majority of these pests are coleopterans and the most damaging species of storage insects belong to the genera Sitophilus, Oryzaephilus, Acanthoscelides and Tribolium (Marsans, 1987, Khan and Selman, 1988, Vinuela et al, 1993, Pinto et al, 1997, Mowery, et al, 2002 and Beckel, et al, 2007). Numerous studies have documented the effectiveness of plant extracts against insect pests few studies have evaluated the bio-efficacy of R. dentatus and B. pilosa against the stored products pests the present study was carried out to investigate the insecticidal activities of the two plant weeds extracts, compared with Neem oil as a commercial product, against the three stored-product insect pests, A. obtectus (Say), S. oryzae L. and O. surinamensis L
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