Evaluation of Nine Botanical Powders against Infestation of Callosobrucus maculatus (F.) (Col.: Bruchidae)

Insect pests of stored products are responsible for considerable economic losses to stored grains. In many storage systems, fumigants are the most economical and convenient tool for managing stored-grain pests not only for their ability to kill a broad spectrum of pests but also for their easy penetration into the commodity while leaving minimal residues. There are major setback to use the synthetic insecticides including the risk to the consumer, high cost of procurement, effects on non-targeted, as well as development of pest resistant strains and toxic residue in crops. Thus, there is an urgent need to develop economic, safe and environmental friendly fumigant alternatives. Recent studies has been indicated that plant secondary metabolites that may significantly affect plant resistance to parasites. Many researchers have studied insecticidal and oviposition deterrent effects of plant materials and have reported some compounds as appropriate agents in controlling pest infestation in stored products. In comparison with chemical pesticides, plant materials are less harmful not only to the environment but, in most cases, to humans and at times, may be used in treating human diseases as well. The present study was performed to evaluate the fumigant toxicity of dried leaf powders from nine medicinal plants against cowpea weevil, Callosobruchus maculatus (F.) (Coleoptera: Bruchidae).
The individuals of C. maculatus was obtained from laboratory stock cultures maintained in the Department of Plant Protection, Faculty of Agriculture, Lorestan University, Khorramabad, Iran. The beetles were reared on cowpea seeds and one to three- day- old male and female adults were used for bioassay tests.
Plant materials: The fresh leaves of Chamaemelum nobilis L., Thymus serpyllum L. and Ferulago angulate (Schlecht) Boiss. were collected from Sephid Kouh in west Khorramabad. The aerial parts of Achillea millefolium L., and Mentha pulegium L. were collected from 30km north of Khoramabad and Anethum graveolens L. and Ocimum basilicum L. were collected from Serab-Changai farms, Khoramabad. Collected leaves were shadow dried under good ventilation and milled into fine powder using electric blender. Powders of two common spices, Cinnamomum zeylanicum Blume and Zingiber officinale Rosc were purchased from local market in Khorramabad.
Inhalation toxicity- Tests: Fumigant toxicity of the botanical powders was tested against 1-3 days old adults of C. maculatus. 10 adults of C. maculatus was placed inside glass vials (volume: 100 ml) without considering the sex ratio. Since, according to the trial experiment, fumigant toxicity of the studied botanical powders significantly differed, therefore, different concentrations were prepared. This experiment was carried out in completely randomized design with five replicates incubated in the dark at 30±2°C and 65±5% RH. After 48 h of exposure period, the number of dead and live insects in each bottle was counted. Insects were considered whether they were dead if they could not move their appendages. Insect mortality percentage was calculated using the Abbott correction formula for natural mortality in untreated controls. Data were transformed to reduce variance heterogeneity. Data were analyzed using one-way analysis of variance followed by Duncan test to estimate statistical differences between means. Based on the mortality data obtained from different concentrations, LC50 values were determined using POLO-PC program.
Oviposition deterrence was studied with two pairs of new adults beetles treated with different concentrations of botanical powders. After five days, number of eggs was recorded in treatments and control and oviposition deterrence was calculated as follows:Oviposition deterrence = (1–NEt / NEc)100
Where: Nt = Number of eggs in treatment
Nc = Number of eggs in control
Results showed that all the tested plant powders showed insecticidal and oviposition deterrent activity against C. maculatus. M. pulegium powder showed the strongest insecticidal activity against cowpea weeviland at the concentration of 1 g/lair caused 96% mortality of this pest. The LC50 values estimated for the plants, M. pulegium, C. zeylanicum, Z. officinal and O. basilicum were 0.31, 2.47, 4.01 and 4.81 g/lair, respectively. Powders of M. pulegium, Z. officinale and C. zeylanicum at concentration of 1 g/lair caused 91.74, 90.08 and 90.25% oviposition deterrent of C. maculatus, respectively. Overall, the powder of these plants, especially M. pulegium, could be recommended as low-risk and inexpensive pesticides in rural areas.
The results demonstrated that all the botanical powders exhibited insecticidal activity and oviposition deterrent against the C. maculatus. The results indicated that the powder of M. pulegium (LC50 = 0.34 μL/Lair) is the most toxic plant powder against C. maculatus.