Molecular markers for identification of the hyperparasitoids Dendrocerus carpenteri and Alloxysta xanthopsis in Lysiphlebus testaceipes parasitizing cereal aphids.

Polymerase chain reaction (PCR)-based molecular markers have been developed to detect the presence of primary parasitoids in cereal aphids and used to estimate primary parasitism rates. However, the presence of secondary parasitoids (hyperparasitoids) may lead to underestimates of primary parasitism rates based on PCR markers. This is because even though they kill the primary parasitoid, it's DNA can still be amplified, leading to an erroneous interpretation of a positive result. Another issue with secondary parasitoids is that adults are extremely difficult to identify using morphological characters. Therefore, we developed species-specific molecular markers to detect hyperparasitoids. A 16S ribosomal RNA mitochondrial gene fragment was amplified by PCR and sequenced from two secondary parasitoid species, Dendrocerus carpenteri (Curtis) (Hymenoptera: Megaspilidae) and Alloxysta xanthopsis (Ashmead) (Hymenoptera: Charipidae), four geographic isolates of the primary parasitoid, Lysiphlebus testaceipes (Cresson) (Hymenoptera: Braconidae), and six aphid species common to cereal crops. Species-specific PCR primers were designed for each insect on the basis of these 16S rRNA gene sequences. Amplification of template DNA, followed by agarose gel electrophoresis, successfully distinguished D. carpenteri and A. xanthopsis from all four isolates of L. testaceipes and all six cereal aphid species in this laboratory test.

Role of Green Peach Aphid Flights in the Epidemiology of Potato Leaf Roll Disease in the Columbia Basin.

Three distinct and highly predictable green peach aphid (GPA) (Myzus persicae) flights that occur seasonally in the spring, summer, and fall were detected at a southern, central, and northern location in the Columbia Basin of the Northwestern United States. Intensity and timing of the flights was approximately the same at the three locations. Timing and number of alatae captured in the spring and summer flights was associated with heat unit accumulation. The spring flight, which originates on the overwintering peach tree host, colonized but did not introduce potato leafroll virus (PLRV) into virus-free potato plots. The summer flight, which originates from volunteer potatoes and spring herbs originally colonized by the spring flight, did introduce PLRV into virus-free potatoes. The fall flight was too late to affect potato production. When plots contained a point source of PLRV, the virus spread rapidly in a plant-to-plant mode to all plants in plots after aphids arrived in the spring. Rate of spread from point sources of infection was not affected by timing or intensity of the spring flight, but timing of virus spread in the plots depended on time of arrival of the aphids. Once PLRV was introduced to virus-free plots by the summer flight, virus spread to other plants within the plots. GPA overwintered on peach trees. Although GPA apterae and alatae were present on winter annual weed and crop hosts in the fall, none survived winters on these species. In addition to the GPA, one other vector of PLRV, Macrosiphum euphorbiae, was rarely collected in aphid traps. These results suggest that chemical control of aphids could be delayed until mid-July if PLRV-free potato seed were available.