1995 Annual Report for AS95-024
Identifying Pesticides Most Compatible with Parasites of the Citrus Leafminer
Summary
Objectives
The objectives of the research were to develop information on the toxicity of pesticides to a parasite introduced against the citrus leafminer (CLM) in a classical biological control program and to transmit that information to homeowners and citrus nursery and grove managers.
The citrus leafminer (CLM), Phyllocnistis citrella, has caused extensive damage in door yard trees, nurseries, and groves since its introduction into the USA in 1993. The natural enemy Ageniaspis citricola was collected in Australia, cleared through quarantine, reared, and released into citrus groves throughout Florida. A. citricola has established, overwintered, and dispersed from release sites throughout the 860,000 acres of citrus in Florida. The use of toxic pesticides to control other insects, mites, and plant diseases could prevent this natural enemy of the citrus leafminer from providing adequate control.
Approach
Laboratory bioassays were conducted to obtain data on the toxicity of pesticides commonly used in citrus pest management to A. citricola. Two types of bioassays were conducted, one comparing toxicity to adults of both the CLM and natural enemy using a clip- cage which consists of a “sandwich” of citrus leaves treated with water, 0.25-, 0.5-, 1-or 2-fold the field rate of each pesticide. Mortality is assessed after 24 hours.
Oil (used for control of insects, mites, and plant diseases), Align and Neemix (azadirachtin, a natural product from neem trees used as an insecticide), Micromite (diflubenzuron, a growth regulator used as an insecticide), Eclipse (fenoxycarb, a chitin-synthesis inhibitor used as an insecticide), Provado (imidacloprid, a systemic insecticide), Agri-Mek (avermectin, a natural fermentation product from a microorganism used as an insecticide and miticide), Neemgard (neem oil, a mixture of natural products from neem trees used as an insecticide), and Kocide (copper hydroxide, a fungicide regularly used to control fungal diseases in citrus) were tested.
Align, Neemix, Eclipse, Micromite, and Neemgard are relatively nontoxic to adults of both the leafminer and the parasite at all rates tested using clip-cages. Agri-Mek appears to be more toxic to adults of the natural enemy than to adults of the citrus leafminer in the clip-cage tests. When oil was tested, it was toxic to adults of both species, which was surprising because it has a reputation as a product that is useful in IPM programs. When oil residues were allowed to age for 24 or 48 hours before placing adults into the cages, the toxicity to the natural enemy was eliminated, indicating this product is useful in IPM programs because it has a very short residual activity.
Most of the products also were tested using a second method designed to assess the impact of these products on immatures of both the citrus leafminer and the natural enemy. After both tests were completed, two different ratings were compiled, one for that combined the toxicity of each product at the 1-X rate to both adults and immatures of the parasitoid A. citricola (Selectivity Index) and one that rated the product as to whether it was an effective insecticide at the 1-X rate against the target pest, the citrus leafminer (CLM efficacy index). The two were combined into an IPM compatibility index and the products were rated “Compatible, Semi-compatible, and Incompatible”. Agri-Mek was an exception; because this product is so toxic to both the CLM and A. citricola, the Selectivity Index and CLM Efficacy Index (and thus the IPM Compatibility Index) were calculated using the 0.25-X rate.
Results
Neemix + oil, Micromite + oil, Eclipse + oil, and oil after 24 h and 48 h, were compatible with an IPM program because they suppressed CLM populations yet did not kill all the parasites.
Align + oil, Neemgard, and Admire were “Semi-compatible” because they were relatively nontoxic to A. citricola, but they were not highly effective against the CLM. The fish oil was selective and thus compatible as a foliar fertilizer; it did not show insecticidal activity against the CLM under these test conditions. Copper hydroxide, a fungicide, was moderately selective and thus is compatible with an IPM program.
Agri-Mek, even at the 0.25-rate, was so toxic to the CLM that no A. citricola could survive under these test conditions. Because it is such an effective insecticide, Agri-Mek was rated incompatible with an IPM program at the 1-X and 0.25-X rate.
Provado and Ethion were only tested with the clip-cage bioassay because they killed all A. citricola adults at all rates tested. These products were considered “Incompatible” for an IPM program for that reason.
Potential contribution
The information obtained will be delivered to homeowners, nursery and grove managers, cooperative extension personnel, and growers via demonstration plots, publications in newsletters, trade journals, and peer-reviewed journals.
December 1997.