Emamectin

Emamectin (Slice), registered for use in aquaculture in Europe, 3 220t Emamectin benzoate, 14 347 Emanuel Tire process, 21 470—471 Embedded passives, 10 15 Embedding, 10 1-30. See also Encapsulation... 

Emamectin benzoate is a semisynthetic avermectin that is derived from fermentation of avermectin B. It contains a mixture of 4" epimethylamino-4"-deoxy-avermectin B,a and Bjb benzoate salts. Emamectin benzoate is a stomach poison insecticide active against lepi-dopterous pests in vegetables, cotton, maize, peanuts, soybeans, and strawberries. Its oral LD50 in rats is 1516 mg/kg. 

GABA-gated chloride channels Cyclodienes, lindane, phenylpyrazoles, Avermectins, emamectin benzoate, milbemectin Antagonism Chloride channel activators... 

Natural products can sometimes be used in crop protection following suitable chemical modification. A good example of a semi-synthetic compound is Syngenta s insecticide emamectin, prepared by synthetic modification of the natural product abamectin (= avermectin Bi) which, in turn, is obtained by fermentation of the bacterium Streptomyces avermitilis (Figure 1). Emamectin is a highly potent insecticide, used at rates as low as 5-25 g/ha, and it is this that justifies the high costs associated with its production. ... 

Recently, chemical modifications have been carried out with the aim of increasing its insecticidal spectrum, residual activities, and chemical stability. Ivermectin, doramectin, emamectin, eprinomectin, and selamectin have been developed, and KAV-218 has been under development (Fig. 35). 

To date, three compounds from this group of chloride channel activators (aba-mectin, emamectin benzoate, and milbemectin) have been commercialized in crop protection. In addition, a development compound has become known as lepimectin (provisionally approved ISO common name). In this introduction, the origin, synonyms and physicochemical properties of the marketed compounds [1] are summarized (see Tables 29.6.1 and 29.6.2). Further aspects will be discussed in detail in the following sections, such as their mode of action, discovery, chemistry, insecticidal activity, agronomic use, and safety. Several recent reviews cover... 

Emamectin benzoate is produced by chemical synthesis from abamectin (Table 29.6.2) [14-17]. The extreme potency of this compound against Lepidoptera was discovered by Merck scientists [18], Emamectin benzoate was introduced to the market by Novartis (now Syngenta Crop Protection AG) in 1997. 

Emamectin is prepared from abamectin in four chemical steps [14-17]. Therefore, it is also a mixture of the two homologs Bia and Bib. The allylic hydroxy group at C5 of avermectins is the most reactive in the molecule. It has to be protected before reactions on the C4" hydroxy group can be performed. Reaction with t-butyl-dimethylchlorosilane and imidazole in N,N-dimethylformamide gives the 5-0-t-butyldimethylsilyl ether (Scheme 29.6.1). 

Table 29.6.5 Activity of emamectin against mites and insects.

Jansson and Dybas [5] have reported a summary of the comparative toxicity of abamectin and emamectin against 28 arthropod pests of agricultural importance. 

Thus, it is reported that 4"-desoxy-4"-amino-avermectin Bi (14) [i.e., the (S)-isomer at C4" Scheme 29.6.5] is five times less active against Spodoptera eridania (S.e.) than 4"-desoxy-4"-epi-amino-avermectin Bi (15) [i.e., the (R)-isomer at C4"]. Emamectin 13 has the highest activity against S. eridania among all 4"-amino derivatives. On the other hand, all 4"-amino derivatives are less active against Tetranychus urticae than abamectin (1). 

Table 29.6.6 summarizes selected toxicological and ecotoxicological data [1] of abamectin, emamectin benzoate, and milbemectin. The products are removed... 

In general, all three products are safe for target crops [53]. Their impact on populations of predatory arthropods is lower than on target pests [46]. This has been the subject of many studies, in particular for abamectin [54-58], and for emamectin [59-61]. For example. Hoy and Cave [56] showed that abamectin is more toxic to Tetranychus urticae than to the predator Metaseiulus occidentalis. They also showed that field-aged residues of abamectin were safe for Metaseiulus occidentalis after 2 days. 

Emamectin benzoate is used in many countries, mainly in all kinds of vegetable crops, such as brassicas, fruiting and leafy vegetables, but also in cotton (Table... 

Emamectin benzoate controls all agronomically important Lepidoptera in vegetables and cotton. Typical application rates for these uses are in the range 8.4-16.8 g-a.i. ha . Some additional uses are the control of some pests in tea and of pine wood nematode in pine trees in Japan. 

The long-lasting activity of fiubendiamide on cabbage leaves has been investigated under glasshouse conditions (Fig. 31.8). Fiubendiamide showed sufficient residual activity on treated leaves for more than 4 weeks. The activity was on the level of cyhalothrin, and superior to methomyl and emamectine-benzoate. It was also confirmed that the control efficacy of fiubendiamide persists for about 2-3 weeks in many crops under field conditions at the recommended rate in Japan, 100 and 50 mg-a.i. [9, 13]. 

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