Imidacloprid Movement into Fungal Conidia is Lethal to Mycophagous Beetles

Abstract

1. Applications of systemic pesticides can have unexpected direct and indirect effects on nontarget organisms, producing ecosystem-level impacts. 2. We investigated whether a systemic insecticide (imidacloprid) could be absorbed by a plant pathogenic fungus infecting treated plants and whether the absorbed levels were high enough to have detrimental effects on the survival of a mycophagous beetle. Beetle larvae fed on these fungi were used to assess the survival effects of powdery mildew and imidacloprid in a factorial design. Fungal conidia were collected from treated and untreated plants and were tested for the presence and concentration of imidacloprid. 3. Survival of beetles fed powdery mildew from imidacloprid-treated leaves was significantly lower than that of beetles from all other treatments. 4. Imidacloprid accumulated in fungal conidia and hyphae was detected at levels considered lethal to other insects, including coccinellid beetles. 5. Water-soluble systemic insecticides may disrupt mycophagous insects as well as other nontarget organisms, with significant implications for biodiversity and ecosystem function.

Indirect Effect of Pesticides on Insects and Other Arthropods

“…The persistence of systemic insecticides in tissues of plants and fungi becomes a death trap for non-target mycophagous insects such as the twenty-spotted ladybeetle, Psyllobora vigintimaculata (Coleoptera: Coccinellidae), which feeds on conidia and hyphae of powdery mildews (Erysiphales). These pathogenic fungi grow on the treated plants and act as reservoirs of the insecticides applied (i.e., imidacloprid), indirectly poisoning the ladybugs that are the natural control of the fungi [ 83 ]. Similarly, systemic insecticides can adversely affect predatory bugs such as Orius insidiosus (Hemiptera: Anthocoridae), which often feed on plant sap [ 84 ], and the lacewing Chrysoperla carnea (Neuroptera: Chrysopidae), which also feeds on extra-floral nectar containing residues [ 85 ].…”

Insights into the Toxicity and Degradation Mechanisms of Imidacloprid Via Physicochemical and Microbial Approaches

“…However, it has been shown that when the stressor is stopped, the organisms recover without any long-term effects [51]. For the first time, researchers have documented the tritrophic movement of imidacloprid from plants to fungi to insects, resulting in a significant number of indirect deaths of non-target mycophasimilar beetles, and adversely affecting an important set of pathogen biological control pathways [52]. Compared to other non-target aquatic insects, neonicotinoid insecticides cause less harm to the early-life stages of the ramshorn snail and Planorbella pilsbryi [53].…”