Comparative toxicity and selectivity of the neonicotinoid insecticides acetamiprid and imidacloprid against the cotton white fly bemisia tabaci, the cotton leaf worm spodoptera littoralis and the honey bee Apis mellifera

Abstract EN

Bioassays were conducted to study comparative and selective toxicity of commercial formulations of the neonicotinoid insecticides acetamiprid (Mospilan 20% SP) and imidacloprid (Imaxi 35% SC) against Bemisia tabaci (Genn.) and Spodoptera littoralis (Boisd.) using leaf dipping technique as well as Apis mellifera L.

by orally mixing with food media.

Based on the obtained LC50 values, acetamiprid was more toxic to the tested adult and nymphal stages of B.

tabaci than imidacloprid.

The adult stage was more susceptible than nymph.

Acetamiprid showed higher toxicity to eggs, the 2nd and 4th instar larvae of S.

littoralis than imidacloprid.

Moreover, eggs were more susceptible to the two tested insecticides than the larval instars, and the 4th instar larvae were the least susceptible.

Acetamiprid applied orally to honey bee workers at a field rate (50 μg a.i./ml) caused 3.33 % mortality with no symptoms of toxicity 24 hr.

post treatment.

The field rate of imidacloprid (265 μg a.i./ml) gave 90% mortality and obvious symptoms of poisoning were recorded 10 minutes after exposure.

The LC50 value for imidacloprid was 59.83 μg a.i./ml.

The results revealed that the cyano-substituted compound (acetamiprid) was more toxic to the tested insect pests than the nitro-substituted compound (imidacloprid) and the later was highly toxic to honey bee.

So, the efficiency and selectivity of neonicotinoid insecticides are related to the chemical group of the compound as well as the species and developmental stage of the insect