The use of imidacloprid as a systemic insecticide to trees is associated with adverse effects on non-target insects and earthworms

Imidacloprid can be applied as a systemic insecticide to trees by direct stem injections or by soil injections and drenches, and be indirectly introduced to aquatic systems via leaf fall or leaching, which may pose a risk to natural decomposer organisms. When applied directly to aquatic microcosms to simulate leaching from soils, imidacloprid was shown to be highly toxic to aquatic insects. Imidacloprid at realistic field concentrations in maple leaves had adverse effects on aquatic insects and earthworms. Imidacloprid at realistic concentrations in leaves can inhibit leaf litter breakdown through adverse effects on decomposer invertebrates. When imidacloprid is applied as a systemic insecticide to the soil around trees it may cause adverse effects on earthworms.

Sources:
Kreutzweiser DP et al (2007) Ecotoxicology and Environmental Safety 68: 315-325 (see attachment)
Kreutzweiser DP et al (2008) Bull Environ Contam Toxicol (see attachment)
Kreutzweiser DP et al (2008) J Environ Qual 37: 639-646 (see attachment)
Kreutzweiser DP et al (2009) Ecotoxicology and Environmental Safety 72: 1053-1057 (see attachment)
Kreutzweiser DP et al (2008) Pest Manag Sci 64:112-118 (see attachment)