Guayule Resin Antifeedant Activity Against the Colorado Potato Beetle

Among the many applications of guayule (Parthenium argentatum Gray), the use of its resin as a biopesticide has gained much attention in the last few years as it would allow to organically manage important agricultural pests as the Colorado potato beetle (Leptinotarsa decemlineata Say). It is one of the most damaging insect pests to the potato economy worldwide, difficult to control by conventional methods due to the development of resistance to chemical insecticides. Therefore, the aim of this work was to evaluate the activity of guayule resin in affecting the feeding behavior of L. decemlineata. To this end, a short-term feeding choice assay was designed in which the beetles could choose between solvent-treated control leaves or leaves treated with either crude guayule resin 100 µg/cm2, crude guayule resin 50 µg/cm2, refined guayule resin 5 µg/cm2, or low molecular weight rubber 5 µg/cm2. The assay was performed in duplicates and lasted six hours under controlled conditions. After, unconsumed leaf areas were measured, and the feeding inhibition index calculated (% FI). For all the treatments tested, quite a lot of variability was observed between the two replicates. Even so, it was observed that a treatment with guayule resin moderately inhibited the feeding of the beetle, showing a % FI of around 54% for crude guayule resin 100 µg/cm2 and refined guayule resin 5 µg/cm2, and of around 40% for crude guayule resin 50 µg/cm2. As for the treatment with low molecular weight rubber, this showed a negative % FI, indicating not only that it does not inhibit feeding, but also that it promotes feeding. Consequently, it seems that guayule resin exerts some antifeedant effect against L. decemlineata, probably due to active compounds and not to a contact effect derived from the sticky texture of the rubber, which makes guayule resin a potential product in the integrated pest management programs of the Colorado leaf beetle.