DNA detection methods in aphid honeydew: Implications for wheat biological control

Molecular techniques to assess predation are valuable tools for identifying trophic linkages in agroecosystems and can aid in implementing biological control programs.  PCR-based gut content analysis detects predator-prey relationships to ultimately help suppress major pests.  Numerous crops are plagued by aphids (Hemiptera: Aphididae) due to their rapid population growth and ability to vector plant viruses.  Detection of aphid DNA in the guts of predators has helped us further understand these pests and how they interact with natural enemies.  However, interactions other than predators consuming aphids may play a role in these agricultural food webs and need to be investigated.  Therefore, the objective of this study was to determine whether we could detect the presence of aphid DNA in honeydew, the sugary secretion given off by aphids, using the same DNA extraction and PCR methods as for gut content analysis. This project focused on grain aphid pests, the bird cherry-oat aphid, Rhopalosiphum padi, and the English grain aphid, Sitobion avenae.  Using previously optimized aphid primers and a variety of techniques, we found that aphid DNA was not detectable in honeydew. These results imply that, when using molecular gut content analysis specifically for aphid DNA detection, the presence of honeydew will not lead to false detection of aphid predators.  This will, in turn, lead to more accurate descriptions of predator-prey relationships in agroecosystems.  The implications of these results will be discussed as they relate to conservation biological control in winter wheat.