Since ancient times, plant products were used in various aspects. However, their use against pests decreased when chemical products became developed. Recently, concerns increased with respect to public health and environmental security requiring detection of natural products that may be used against insect pests. In this study, 41 plant extracts and 11 oil mixtures were evaluated against the yellow fever mosquito, Aedes aegypti (Linnaeus), the malaria vector, Anopheles stephensi (Liston), and the filariasis and encephalitis vector, Culex quinquefasciatus (Say) (Diptera: Culicidae) using the skin of human volunteers to find out the protection time and repellency. The five most effective oils were those of Litsea (Litsea cubeba), Cajeput (Melaleuca leucadendron), Niaouli (Melaleuca quinquenervia), Violet (Viola odorata), and Catnip (Nepeta cataria), which induced a protection time of 8 h at the maximum and a 100% repellency against all three species. This effect needs, however, a peculiar formulation to fix them on the human skin.

Mosquitoes in the larval stage are attractive targets for pesticides because mosquitoes breed in water, and thus, it is easy to deal with them in this habitat. The use of conventional pesticides in the water sources, however, introduces many risks to people and/or the environment. Natural pesticides, especially those derived from plants, are more promising in this aspect. Aromatic plants and their essential oils are very important sources of many compounds that are used in different respects. In this study, the oils of 41 plants were evaluated for their effects against third-instar larvae of Aedes aegypti, Anopheles stephensi and Culex quinquefasciatus. At first, the oils were surveyed against A. aegypti using a 50-ppm solution. Thirteen oils from 41 plants (camphor, thyme, amyris, lemon, cedarwood, frankincense, dill, myrtle, juniper, black pepper, verbena, helichrysum and sandalwood) induced 100% mortality after 24 h, or even after shorter periods. The best oils were tested against third-instar larvae of the three mosquito species in concentrations of 1, 10, 50, 100 and 500 ppm. The lethal concentration 50 values of these oils ranged between 1 and 101.3 ppm against A. aegypti, between 9.7 and 101.4 ppm for A. stephensi and between 1 and 50.2 ppm for C. quinquefasciatus.

The persistency of larvicidal effects of 13 oils (camphor, thyme, amyris, lemon, cedarwood, frankincense, dill, myrtle, juniper, black pepper, verbena, helichrysum, and sandalwood) was examined by storage of 50-ppm solutions under different conditions (open, closed, in the light, and in the dark) for 1 month after the preparation of the solutions. The stored solutions were tested against Aedes aegypti larvae for four times during the storage period. Some oils under some conditions stayed effective until the last test, while some solutions had lost their toxicity during a short time after preparation. Thus, the mode of storage is absolutely important for the larvicidal effects. The fresh preparations were always the best.

The aim of this study was to detect the role of some mosquito organs in their sensation of repellent materials. A total of 250 females (15 days old) of the target species Aedes aegypti and Anopheles stephensi were prepared and divided into five groups: group 1, without antenna; group 2, without maxillary bulbs; group 3, without proboscis; group 4, without frontal tarsus; and group 5, normal females as control. A mixture of five oils containing Litsea cubeba 1%, Melaleuca leucadendron 1%, Melaleuca quinquenervia 1%, Viola odorata 1%, and Nepeta cataria 1% was included in a complex solvent containing 20% genapol, 10% polyethylene glycol, 20% ethanol, and 50% water. Furthermore, Bayrepel was used in this experiment at a 20% concentration in the same solvent. Pure water was used as control in this study. The test was carried out by spreading 100 microl of the repellent material or water on a 30-cm2 exposure area of a human volunteer's arm. In A. aegypti, the biting and landing percentages increased significantly in those mosquito groups that lacked some organs (especially maxillary bulbs), while in A. stephensi, it became not clear which organ is responsible for perception of repellents.

Degradation line of cypermethrin were studied in different samples of tomato fruits, water, and soil from ogla oasis in the desert environment of Cyrenaica, -Libya. The targeted insecticide was applied to the tomato crop, water, and soil of the studied area with the recommended dose. Representative samples from all three subjects were taken daily which started from the first day of treatment to the 20 th days of experimentation. Extraction and cleanup were conducted on the 20 th days and finely detection of the residues was measured by using Gas chromatography (GC-ECD) instrument. Results of the study revealed 0.06, 1.06, and 2.44 ppm insecticide concentration on the first sampling date from tomato fruits, water, and soil respectively. However after one week 33, 56 and 65% reduction in insecticide concentration was reported in tomato fruits, water and soil respectively. After 2 weeks the reduction percentage was reported 66%, 88%, and 93% chronologically, and the degradation exert 91%, 97%, and 99.1% in the same order at the last sampling date. Results concluded that the trends of cypermethrin degradation were fluctuating and slow in tomato fruits while in water and soil it appears regular. However the degradation in soil was the fastest.