Factors affecting content and bioefficacy of neem (Azadirachta indica A. Juss.) phytochemicals used in agricultural pest control: A review

• Phytochemical contents in neem are affected by agronomic practices.
• Bioefficacy of neem crude extracts and allelochemicals are influenced by weather.
• Insect life stage and modes of action of allelochemicals are major factors for effectiveness.
• Compatibility and synergism play important roles in enhancing bioefficacy.
• Economics of treatment and environmental danger need to be considered.

Neem-based products including traditional preparations and formulations have been used extensively for the control of insect pests attacking agricultural crops. Content of phytochemicals extracted from different parts of the neem plant varies considerably due to abiotic and biotic factors from collection of the raw material to extract preparation and product formulation. Likewise, effectiveness of crude or synthesized material used in the field or laboratory may be influenced by storage conditions, content of active ingredient (especially azadirachtin), insect species and its growth stage, type of formulation and synergism of products with other control measures. In this paper, the direct and indirect actions of neem phytochemicals on insect pests are described and practical implications for future pest control strategies are discussed.