No abstract

The Russian wheat aphid, Diuraphis noxia, an invasive phytotoxic pest of wheat, Triticum aestivum, and barley, Hordeum vulgare, causes huge economic losses in Africa, South America, and North America. Most acceptable and ecologically beneficial aphid management strategies include selection and breeding of D. noxia-resistant varieties, and numerous D. noxia resistance genes have been identified in T. aestivum and H. vulgare. North American D. noxia biotype 1 is avirulent to T. aestivum varieties possessing Dn4 or Dn7 genes, while biotype 2 is virulent to Dn4 and avirulent to Dn7. The current investigation utilized next-generation RNAseq technology to reveal that biotype 2 over expresses proteins involved in calcium signaling, which activates phosphoinositide (PI) metabolism. Calcium signaling proteins comprised 36% of all transcripts identified in the two D. noxia biotypes. Depending on plant resistance gene-aphid biotype interaction, additional transcript groups included those involved in tissue growth; defense and stress response; zinc ion and related cofactor binding; and apoptosis. Activation of enzymes involved in PI metabolism by D. noxia biotype 2 aphids allows depletion of plant calcium that normally blocks aphid feeding sites in phloem sieve elements and enables successful, continuous feeding on plants resistant to avirulent biotype 1. Inhibition of the key enzyme phospholipase C significantly reduced biotype 2 salivation into phloem and phloem sap ingestion.

Estimates about which scale insect species are most frequently encountered in U.S. landscapes and commercial production systems are largely anecdotal. This survey of records maintained across about 15 years within the National Plant Diagnostic Network (NPDN) National Data Repository (NDR) returned information from 10,671 records of 192 scale insect species and 23 suspected species that were associated with ornamental plants. This broad species diversity challenges our ability to effectively train diagnosticians, can confound species identification accuracy, and impedes outreach efforts and resource development. To help focus future efforts in the development of outreach resources and diagnostic training guides, lists were assembled that identified the 60 top-ranked soft, armored, mealybug, and other scale insect taxa most frequently diagnosed within NDR records. Diagnostic service records from Georgia, North Carolina, South Carolina, and Tennessee provided more extensive information regarding sites or client types from which submitted samples originated. Results are being used to develop web-based, image-rich guides to key scale insect taxa in the southeastern United States that will explain life cycles, behaviors, and biology for pest species. These web-based guides can be exploited to optimize pest management actions.