BACKGROUND: Ants often compete with other ants for resources. Although formic acid is a common defensive chemical of formicine ants, it does not occur in any other subfamilies in Formicidae. No information on toxicity of formic acid to red imported fire ants, Solenopsis invicta, is available. This study examined its contact and fumigation toxicity to S. invicta in the laboratory.RESULTS: In a contact toxicity bioassay, 24 h LD50 values of formic acid for workers ranged from 124.54 to 197.71 µg ant−1. Female alates and queens were much less sensitive to formic acid than workers. At a concentration of 271.72 µg ant−1, which killed 81.09 ± 16.04% of workers, the 24 h mortality was up to 39.64% for female alates and 38.89% for queens. In fumigation bioassays, 24 h LC50 values ranged from 0.26 to 0.50 µg mL−1 for workers, 0.32 µg mL−1 for male alates and 0.70 µg mL−1 for female alates. Complete mortality (100%) in queens occurred 24 h after they had been exposed to 1.57 µg mL−1 of formic acid. At a concentration of 2.09 µg mL−1, KT50 values ranged from 23.03 to 43.85 min for workers, from 37.84 to 58.37 min for male alates, from 86.06 to 121.05 min for female alates and from 68.00 to 85.92 min for queens.CONCLUSION: When applied topically, formic acid was significantly less toxic than bifenthrin to red imported fire ants. Although its fumigation toxicity was lower than that of dichlorvos, formic acid had about an order of magnitude higher toxicity to S. invicta than to other insects studied so far. It may be worth investigating the use of formic acid for managing imported fire ants. Published 2012 by John Wiley & Sons, Ltd.
The green peach aphid, Myzus persicae (Sulzer), is a major insect pest of many agronomic and horticultural crops and is distributed worldwide. Aphid management is often based on application of insecticides. However, the aphid is now resistant to many of these and much interest has recently developed in identification of novel alternative insecticides. Venom isolated from the red imported fire ant, Solenopsis invicta Buren, is composed of two groups of alkaloids, piperidines and piperideines, and has shown activity against many organisms including fungi, bacteria, mites and several insects. Prior to the study reported herein, no information on the venom's activity to Myzus persicae has been reported. Both of the alkaloids were active against M. persicae. The 24 h LC 50 values were116.6 and 91.5 ppm for the piperideine and piperidine extracts, respectively. Based on overlap of the 95% fiducial limits the LC 50 values for the two alkaloids did not significantly differ. At the high dosages, mortality occurred in as few as four hours and all treated aphids were dead by six hours. Little additional mortality was detected in the 48-h observation. Both piperideine and piperidine extracts isolated from red imported fire ant venom possess sufficient activity to cause death of green peach aphids and at high dosages, death occurs rapidly. In the search for new replacements to synthetic insecticides, these extracts may offer a novel but potentially successful alternative.
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