Deltamethrin and fenitrothion

2 Deltamethrin and fenitrothion Sometimes interactions may be detected even when an exact mechanism is unknown. As an example from real life, we can look at locust control in Africa. 

The LD50 of deltamethrin alone was 1.2 pg/g of insects, whereas fenitrothion had an LD50 of 3.5 pg/g of insects. It is shown that the LD50 of mixtures of various compositions is lower than expected in cases of additivity. Hundreds of insects were used to determine the plotted LD50 doses of the mixtures. The great scatter illustrates the inborn uncertainty of such determinations. All the points are well inside the line for additivity, and some kind of potentiation is evident. 

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Figure 2.7 An isobologram of Locusta migratoria given mixed doses of deltamethrin and fenitrothion. Given separately, an LD50 dose of deltamethrin is 1.2 pg/g and of fenitrothion is 3.5 pg/g. The figure is based on data provided by Baard Johannessen and will be later published in full text.

Observing the amount and variety of pesticides analyzed by GC chromatography we decided to observe 14 of the most represented pesticides Prometryn, Deltamethrin, Fenitrothion, Tebuconazole, Buprofezin, Malathion, Myclobutanyl, Atrazine, Acetochlor, Bifenthrin, Alachlor, Pendimethalin, Dichlonuid and Trifluralin. 

Locust (Locusta migratoria) is an important pest in Africa. In order to find a suitable pesticide or pesticide mixture, fenitrothion or deltamethrin was tried alone or in combinations by B. Johannesen, a Food and Agriculture Organizaton (FAO) junior expert working in Mauritius. Dilution series of mixtures with different compositions were made and the LD50 values of these mixtures were determined. These values were plotted as shown in Figure 2.7. We see that the two pesticides potentiate each other. 

Some parameters affect the conversion of nonflu-orescent compounds into fluorescent ones, e.g., UV irradiation time and the nature of the solvent used (see Table 1). For example, pesticides such as fenvalerate, diflubenzuron, and deltamethrin are efficiently converted into fluorescent products (high signal with short irradiation time) in protic solvents, while for fenitrothion and chlorpyriphos polar apro-tic solvents are the choice. Comparing the analytical performances of the photoconversion method with other derivatization approaches, it can be considered a rapid, sensitive, and precise method for quantifying several classes of pesticides in stationary media and as postcolumn detection mode in HPLC and in FIA. 

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