A storage stable, efficacious pesticide formulation is provided that is dilutable by the user and contains azadirachtin (AZA) and a pyrethrin or pyrethroid (PYR), and optionally an aprotic solvent and non-ionic, substantially water-free emulsifier. A sufficient amount of the PYR is provided to complex with the AZA A on opposite sides of the molecular structure thereof, thereby preventing rearrangement of the AZA A molecule in the presence of moisture that would result in hydrolysis and decomposition of AZA A. The AZA-PYR combination is sufficiently chemically stable such that less than 10% of the AZA A is decomposed when the formulation is subjected to an accelerated aging test for 30 days at 40°C in a sealed container. The molar ratio of PYR to AZA A is preferably within the range of 0.5/1 - 10.5/1, more preferably within the range of 1.5/1-7/1, and most preferably with the range of 3/1-6/1. A solvent, when provided, should be in the range of about 70% to about 90% by weight based on the weight of the formulation, and the emulsifier should be within the range of about 0% to about 20%.
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