Dose-responses of the citrus leaf miner to several insecticides commonly applied in Florida

The citrus leafminer (CLM), Phyllocnistis citrella Stainton (Lepidoptera: Gracillariidae), was first detected in Florida in 1993 and quickly spread throughout the state. CLM oviposit on young citrus shoots. Damage by mining larvae reduces photosynthesis, causes leaf malformation, and increases susceptibility to canker. Although effectiveness of several reduced-risk and broad-spectrum chemical insecticide formulations has been confirmed in field trials, dose -response relationships have not been studied in detail.  The reliance on chemicals to control CLM populations has certainly increased selective pressures that may lead to resistance. However, resistance evaluation relies on initial quantification of baseline responses of susceptible populations.

Here, we present results of laboratory bioassays conducted to evaluate baseline susceptibilities using individuals from a susceptible laboratory colony. Tested insecticides included the commercial reduced-risk formulations: Micromite (diflubenzuron), Intrepid (methoxyfenozide), and Delegate (spinetoram). Other formulations tested included some that may be applied to CLM populations as part of control efforts for these insects and other citrus pests. These include: Agri-Mek (abamectin), Actara (thiamethoxam), Exirel (cyantraniliprole), and the broad-spectrum insecticides Danitol (fenpropathrin), and the organophosphate, Dimethoate. We estimated the concentration-response relationships for CLM adults and larvae to these insecticides using probit analysis. Results indicated excellent efficacies for Actara, Delegate, Agri-Mek, Danitol and Dimethoate for CLM adults and Actara, Agri-Mek, Delegate, Dimethoate, and Intrepid for CLM larvae. Relatively poor efficacy for CLM larvae was achieved with Danitol. Baseline susceptibilities of CLM to these compounds will form the basis for future resistance evaluation work.