We describe polymerase chain reaction (PCR) primers for gut analysis of aphid predators. The primers amplify aphid mitochondrial COII fragments ranging in size from 77 to 386 bp. Using these primers, we were able to distinguish six species of US Great Plains cereal aphids, including two congeners, Rhopalosiphum maidis (Fitch) and R. padi (L.), and to detect them in extracts of coccinellid and chrysopid predators. We devised a protocol for deriving half-lives of detectability for the DNA of a single aphid consumed by predators maintained under simulated field dietary and temperature conditions. Using this protocol and primers that amplify a 198-bp fragment, we determined statistically different half-lives of detectability for a single R. maidis of 3.95 h in Chrysoperla plorabunda (Fitch) and 8. 78 h in Hippodamia convergens Guerin. The detectability half-life for a 339-bp R. maidis fragment was statistically longer in C. plorabunda but not in H. convergens. The sensitivity of the assay for the 198-bp fragment is 10-7 aphid equivalents. For species-specific predator gut analysis, PCR is superior to monoclonal antibody technology, giving comparable detectability half-lives with lower expense, much shorter development times, and greater certainty of a successful outcome.

Identifying key cereal aphid predators by molecular gut analysis

The predator and parasitoid fauna associated with cereal aphids is described, emphasizing the fauna associated with classical biological control efforts against the greenbug and Russian wheat aphid. We focus on literature from North America and include work from Europe and elsewhere when it is desirable to draw contrasts between approaches that affect cereal aphid biological control. Effects on natural enemies of cereal aphids are described that appear associated with plant traits that are innate, bred, or induced by aphid feeding. Examples of habitat manipulations, within and bordering cereal fields and within the broader landscape in which cereal production resides, affecting predators and parasitoids of cereal aphids are presented. These mediating effects of host plant and habitat manipulations on cereal aphid biological control provide significant and underexplored avenues to optimize cereal aphid management.

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Biological control of cereal aphids in north america and mediating effects of host plant and habitat manipulations.

A multi-step bioassay to assess the effect of the deltamethrin on the parasitic wasp Aphidius ervi

Breeding Wheat for Resistance to Insects

1. Consequences of variation in food plant quality were estimated for a system consisting of two monophagous noctuid herbivores and three ichneumonid parasitoids. 2. In a natural population, pupal weights of the herbivores in this system, Nonagria typhae and Archanara sparganii, were found to be highly variable. Pupal weights increased strongly and consistently with the increase in the vigour of the host plant, Typha latifolia, providing support for the plant vigour hypothesis. Correspondingly, as the moths do not feed as adults, a strong, positive correlation between host vigour and fecundity of the herbivores would be expected. 3. There were strong and positive relationships between adult body sizes of the parasitoids and the sizes of their lepidopteran hosts. Moreover, a direct positive link between plamt quality and parasitoid size was documented. 4. For all three parasitoids, cascading effects of plant quality on body size were weaker than for the herbivores. Differences in the importance of adult feeding and oviposition behaviour suggest that dependence of fitness on body size is also weaker in the parasitoids than in the moths. It is therefore concluded that the numerical response of the herbivore population to a change in plant quality should exceed the corresponding response in the parasitoids. 5. The results of this work imply that variation in plant variables may affect performance of different trophic levels to a different extent. It is suggested that the importance of adult feeding for the reproductive success (capital vs. income breeding strategies) in both herbivores and parasitoids is an essential aspect to consider when predicting responses of such a system to changes in plant quality.

Direct and indirect effects in host-parasitoid interactions: ecological and evolutionary consequences

Host aphids of the parasitoid Diaeretiella rapae (M’Intosh,) are defined for Washington State, together with a listing of world findings. Specifics are given on host habitats frequented by the parasitoid, comparative population abundance, associated parasitoid species, and host switching. D. rapae is a common parasitoid of Brachycorynella asparagi (Mordvilko), Hayhurstia atriplicis (L.), Brevicoryne brassicae (L.), Diuraphis noxia (Kurdjumov), and sometimes Myzus persicae (Sulzer). In total, 19 species of aphids were positively linked with D. rapae and 6 are reported as hosts for the first time— Acyrthosiphon lactucae (Passerini), Phorodon humuli (Schrank), Dysaphis plantaginea (Passerini), Brachycaudus tragopogonis (Kaltenbach), Uroleucon ivae Robinson, and Braggia sp. D. rapae was shown to switch or alternate successfully between hosts, which suggests that certain host habitats might be used in conjunction with farmlands to enhance host opportunities for the parasitoid and improve its population stability. Two of its primary aphid hosts, B. asparagi and D. noxia, reached pest status shortly after their arrival in Washington but are less problematic today, in part at least because of host switching and acceptance by D. rapae.

Host range and habitats of the aphid parasitoid Diaeretiella rapae (Hymenoptera: Aphidiidae) in Washington State.

Aphid parasitoids (Hymenoptera: Braconidae: Aphidiinae) of Northwest USA.

New information is provided on the small-grain aphid parasitoids of eastern Washington—species population diversity, relative abundance, hosts, and spatial and temporal distribution across differing precipitation and cropping zones. In total 13 species of primary parasitoids were discovered attacking grain aphids: Aphelinus albipodus Hayat & Fatima, A. asychis Walker, A. varipes (Foerster), Aphidius avenaphis (Fitch), A. ervi Haliday, A. matricariae Haliday, Diaeretiella rapae (M'Intosh), Ephedrus sp., Lysiphlebus testaceipes (Cresson), Monoctonus washingtonensis Pike & Star´y, Praon unicum Smith, P. occidentale Baker, and P. yakimanum Pike & Starý. The predominant parasitoids were D. rapae on Russian wheat aphid, Diuraphis noxia (Kurdjumov); L. testaceipes on bird cherry-oat aphid, Rhopalosiphum padi (L.) and corn leaf aphid, R. maidis (Fitch); and A. avenaphis, A. ervi , and D. rapae on English grain aphid, Sitobion avenae (F.). This study provides baseline information essential for assessing future changes in aphid parasitoid species dynamics for eastern Washington. A comprehensive key to the known primary and secondary parasitoids associated with grain aphids in North America also is provided.

Small-Grain Aphid Parasitoids (Hymenoptera: Aphelinidae and Aphidiidae) of Washington: Distribution, Relative Abundance, Seasonal Occurrence, and Key to Known North American Species

L. Boydston

Papers

Host range and habitats of the aphid parasitoid Diaeretiella rapae (Hymenoptera: Aphidiidae) in Washington State.

Aphid parasitoids (Hymenoptera: Braconidae: Aphidiinae) of Northwest USA.

Small-Grain Aphid Parasitoids (Hymenoptera: Aphelinidae and Aphidiidae) of Washington: Distribution, Relative Abundance, Seasonal Occurrence, and Key to Known North American Species

Alate aphid viviparae associated with small grains in North America: a key and morphometric characterization.

New species and host records of aphid parasitoids (Hymenoptera: Braconidae: Aphidiinae) from the Pacific Northwest, U.S.A.