A rapid, efficient method for the bioassay of extracts, fractions and compounds for activity against tropical aphids

Abstract

Although aphids remain serious pests, bioassay-guided purification of anti-aphid compounds depends upon assays that are laborious and often have incomplete descriptions of methods. We provide the protocol for a rapid, efficient assay using a 96-well microtiter plate format for testing extracts for activity against the cotton aphid, Aphis gossypii Glover (Sternorrhyncha: Aphididae), and the black bean aphid, Aphis craccivora Koch. Assays of extracts composed of low molecular weight metabolites from 28 species of plants from 15 families from Panamanian forest showed variation in toxicity to A. craccivora. Three metabolite extracts and one protein extract were active, with more than 70% mortality in 72 h, averaged over three independent experiments. For three species of plants with protein extracts having intermediate activity, the metabolite extracts were inactive; hence, the activity probably was due to the toxic proteins, rather than contaminating toxic metabolites.

Keywords:

• Plant metabolites
• protein extracts
• Sternorrhyncha
• artificial diet
• colonies
• clonal
• tropical forest

Acknowledgements

This study was supported by an International Cooperative Biodiversity Groups grant, “Ecologically guided bioprospecting in Panama”, 5-U01-TW01021-05 from the US National Institutes of Health (NIH), US National Science Foundation (NSF) and US Department of Agriculture (USDA) to the Smithsonian Tropical Research Institute. We acknowledge a cooperative research agreement between the Smithsonian Tropical Research Institute (STRI) and the University of Panama. The authors wish to express their thanks for excellent technical advice from L. Harrison and M. Cinciripini (Monsanto Company), logistical support from the University of Panama, facilitation of sample collection by Panama's Autoridad Nacional del Ambiente, plant identification by M. Correa, and excellent technical assistance from N. Ríos, R. Aizprúa, B. Araúz, and N. Flores.