Insecticidal, antifeedant and molluscicidal potential of essential oils extracted from Egyptian plants

The objective of this study was to elucidate the chemical composition of essential oils from five Egyptian plants, namely Citrus reticulata, Schinus terebenthifolius, Mentha microphylla, Lantana camara and Eucalyptus camaldulensis, obtained by hydrodistillation and their biological activity on economic agricultural and public health pests. The isolated essential oils were tested for their larvicidal activity against Culex pipiens and fumigant toxicity against the adults of Culex pipiens, Musca domestica and Theba pisana. The antifeedant, topical, fumigant and residual toxicity of the isolated oils towards the larvae of Spodoptera littoralis were also examined. The isolated oils showed a strong larvicidal activity against the fourth instar larvae of C. pipiens in a concentration dependant manner. The oil of C. reticulata was the most effective among the tested oils followed by the oils of S. terebenthifolius and M. microphylla with LC50 values of 13.85, 20.75 and 22.42 mg/L, respectively. In a fumigant assay on the adults of C. pipiens, the isolated oils showed a potent toxic activity after 30 min of exposure. Eucalyptus camaldulensis oil exhibited the highest activity followed by M. microphylla oil with LC50 values of 0.96 and 2.47 microl/L. The results of the fumigant assay against the adults of M. domestica revealed that the oils were highly toxic after 1 and 24 hours of exposure with M. microcorphylla oil being the most effective. The larvicidal effects of the isolated oils against the third instar larvae of S. littoralis indicated that the assay method is an important factor for determining the toxicity of the isolated oils. The isolated oils showed a pronounced insecticidal potential in fumigant assay while they revealed a moderate to weak activity in both topical and residual assays. When tested for their antifeedant activity, the oils of S. terebenthifolius and L. camara were the most active among the tested oils at concentration of 1000 mg/L. Fumigant toxicity evaluated against the adult of T. pisana revealed that the oil of C. reticulata was the most toxic among the tested oils with LC50 value of 6.79 microl/L. The chemical composition of the isolated essential oils has been analyzed by gas chromatography-mass spectrometry [GC-MS]. Chemically, the major constituents of the oils belong to four main groups: oxygenated monoterpenes, monoterpene hydrocarbons, sesquiterpene hydrocarbons and oxygenated sesquiterpenes. The results obtained in this study suggest that, in addition to their other uses, the isolated oils can also serve as natural pest control agents

Cytological, anatomical and biochemical studies on the side-effect of some pesticides

The invisible side-effects of triazophos and spinosad [insecticides], thiophanate-methyl [fungicide] and 2,4-D [herbicide] on plant were carried out using the bioassay test system of Vicia faba root tips to detect their cytotoxicity. Also, effects on the anatomical and biochemical characteristics were investigated. The obtained data showed that a linear decrease in mitotic index [MI] with increasing pesticide concentration. In addition, a linear correlation between the concentration and percentage of chromosomal abnormalities was recorded in the presently treated pesticides. The EC50 values caused undivided to 50% of total root tip cells were 3.61x10[-6], 1.31x10[-3], 4.85x10[-3] and 35.5 ppm for spinosad, thiophanate-methyl, 2,4-D and triazophos, respectively. The results also revealed that all tested pesticides found to decrease the growth of seedlings by 50 to 60% compared to the control. The normal tissues of stem and root similar to control were obtained in the case of insecticide spinosad and tested fungicide thiophanate-methyl while, malformation of the parenchyma cells and dialysis of the cell walls were observed in the case of herbicide 2,4-D. All tested pesticides significantly decreased the protein content in shoot and root except the herbicide 2,4-D in the case of shoot tissue. The insecticide spinosad increased the DNA content while, insecticide triazophos, fungicide thiophanate-methyl and herbicide 2,4-D reduced the DNA content of shoot and root tissues. It is clear that the effect of tested pesticides depends on pesticide type and plant tissue. In addition, the peroxidase enzyme was high sensitive to the tested pesticides. In similar, all of the tested pesticides shown to be highly esterase inhibitors in the case of shoot tissues. It was clear that there were 5 bands of protein pattern in control sample. The protein bands identical with 95.9 and 56.2 KDa were recorded in all treatment samples. In contrast, the protein band of 40.4 KDa was completely disappeared from the homogenates of all tested treatments, Peroxidase isozyme [58.9 KDa] was appeared in tested fungicide and herbicide treatments. While, the band [30.8 KDa] was disappeared in all treatments. Two major esterase isozymes corresponded to 68.3 and 27.8 KDa were presented. These isozymes were appeared in all pesticide treatments except in the case of spinosad. In general, according to the results of present study it can be stated that; the evaluation of pesticides hazardous effects depends on their side visible effects on the non-target organism did not enough. The invisible side-effect is very important in this response

Effect of some insecticides on the haemolymph of desert locust Schistocerca gregaria forskal

The toxicity and the physiological effects of insecticides, chlorozan, marshal and deltamethnne and the alternative pesticides spinosad and proclaim on the desert locust Schistocerca gregaria were tested. The toxicity index, LC50 values after 24 hrs were 171.16, 44.29 and 410.05 ppm. for chlorozan, marshal and deltamethnne, respectively. Also the values of LC50 after 48 hrs were 425.58 and 101.58 ppm. for spinosad and proclaim, respectively. The effect of all tested insecticides, on the total and different haemocytes count of the 4[th] instar nymphs of Schistocerca gregaria were evaluated. The obtained results revealed that the total haemocyte counts were clearly affected by insecticides tested at LC50 values. Chlorozan and proclaim decreased the total haemocytes count [THCs] 50% compared to control. Also marshal and deltamethrine decreased the total haemocyte count by 35 and 18.3%, respectively. While spinosad showed a slight decreasing in the total haemocyte by 8.9% compared to control. Six different haemocyte types were identified as prohaemocytes [pr], granulocytes [gr], non-granulocytes [n-gr], plasmatocytes [pi], oenocytes [oe] and spherulocytes [sph] cells were monitored. In general, all the tested insecticides decreased the counts of all the haemocyte types. The application of spinosad increased the pr, pi, oe and sph. While it dercreased both n-gr. and gr. The toxicological profile of the tested pesticides described herein characterizes their effects on S. gregaria haemocyte types and the total haemocytes count [THCs] when compared with control. These results could be indicate a new proposed mode of action to those friendly environmental promising compounds

Kinetic investigation into the interaction of chlorpyrifos and thiodicarb with acetylcholinesterase activity from some harmful and beneficial insects

Acetylcholinesterase [AChE] is the target site of organophosphate and carbamate insecticides and is responsible for the intoxication resulting in death of insects. Partially characterization of AChE and its interaction with organophosphate and carbamate has been studies. The inhibition of AChE by two insecticides; chlorpyrifos and thiodicarb was investigated in the head homogenates of two cotton leafworm Spodoptera littoralis strains; laboratory and field srain; cut worm, Agrotis ipsilon and honey bee Apis millefra. The results obtained revealed that the AChE from different insects is identical in us properties. Highly activity of AChE was detected in the head homogenate of adult insect of honey bee. The lowest I[50] value micro M [the highest inhibition potency] was obtained with thiodicarb against all the tested insect species. The lowest inhibition was obtained with thiodicarb and chlorpyrifos against field strain of S littoralis compared to laboratory strain. According to Dixon plots, the inhibition pattern of either chlorpyrifos or thiodicarb was a noncompetitive type