Primary and secondary parasitoids (Hymenoptera) of aphids (Hemiptera: Aphididae) on blueberry and other Vaccinium in the Pacific Northwest.

Blueberry scorch virus, a commercially important Carlavirus in highbush blueberry, Vaccinium corymbosum L., is vectored by aphids (Hemiptera: Aphididae). We surveyed the aphids, primary parasitoids (Hymenoptera: Aphelinidae, Braconidae), and associated secondary parasitoids (Hymenoptera: Charipidae, Megaspilidae, Pteromalidae) on highbush blueberry and other Vaccinium in the Pacific Northwest from 1995 to 2006, with samples concentrated in 2005 and 2006, to lay the groundwork for augmentative biological control. Ericaphis fimbriata (Richards) was the principal aphid. The dominant parasitoid species were Praon unicum Smith, Aphidius n. sp., A. sp., and Aphidius ervi Haliday. Their frequency in relation to the other primary parasitoids varied significantly with geographical area; P. unicum dominated the frequency distribution in southwestern British Columbia, A. n. sp., west of the Cascades, and A. sp. and A. ervi east of the Cascades. Among the secondary parasitoids, pteromalids dominated, and their frequency in relation to the other secondary parasitoids was lowest in southwestern British Columbia. The parasitization rate for P. unicum and A. n. sp. in southwestern British Columbia increased from May or June to a maximum of 0.080 +/- 0.024 and 0.090 +/- 0.084 (SD), respectively, in late July or early August. P. unicum emerged in the spring 4 wk before A. n. sp. The parasitization rate for P. unicum was lower in conventional than organic fields. Whereas aphid density increased monotonically, P. unicum had two spring peaks. A simulation model showed that these peaks could reflect discrete generations. Releases of insectary-reared P. unicum at 150 or 450 DD above 5.6 degrees C, summing from 1 January, may effectively augment the natural spring populations by creating overlapping generations.

Purification of Plasmodium lophurae cathepsin D and its effects on erythrocyte membrane proteins.

The cathepsin D of Plasmodium lophurae was purified using a combination of CM-Sephadex, pepstatin-agarose and Sephadex G-100 chromatography. The plasmodial enzyme was distinct from that of the host red cell and bovine spleen in its low isoelectric point (pI 4.3). The cathepsin D of P. lophurae, as well as plasmodial extracts demonstrating such proteinase activity, were able to digest the membrane proteins of duckling and human red cells at pH 7.4; proteolysis was not inhibited in phosphate-buffered saline by 100 microM pepstatin. Membrane proteins most susceptible to proteolysis were those of the cytoskeleton, notably bands 1 and 2 (spectrin), bands 2.1-2.6 (spectrin-binding proteins) and band 3. Membrane protein degradation by crude plasmodial extracts was partially inhibited by a combination of 10 mM FeCl3, and 10 mM phenylmethylsulfonyl fluoride in phosphate-buffered saline. The changes induced in erythrocyte membrane proteins by exposure to plasmodial cathepsin D parallel the alterations observed in red cell membranes obtained from malaria infected cells. Since the action of the plasmodial protease was confined to the inner surface of the red cell membrane, it is possible that protease-induced modifications in the red cell cytoskeleton could lead to merozoite release.

Parasite defense mechanisms for evasion of host attack; a review.

This review covers some of the basic mechanisms whereby parasites evade host responses. These mechanisms include; antigenic variation, repeated antigenic determinants, induction of suppressor cells, acquisition of host proteins or molecular mimicry, proteinase destruction of host effector molecules, proteinase inhibitor-mediated inhibition of humoral and cellular immune effector arms and immunosuppressive products of parasite arachidonic acid metabolism. Vet. Parasitol.

Predatory role of Neoseiulus fallacis (Acari: Phytoseiidae): spatial and temporal dynamics in Washington red raspberry fields.

The seasonal abundance of spider mites and their predator Neoseiulus fallacis (Garman) (Acari: Phytoseiidae) was determined during three consecutive years in Washington State red raspberry fields. Tetranychus urticae Koch (Acari: Tetranychidae), Eotetranychus carpini borealis (Ewing) (Acari: Tetranychidae), and N. fallacis were commonly found in Skagit and Whatcom Counties. E. carpini borealis colonized the fruiting canes earlier in the season than T. urticae. The two phytophages overlapped in midseason, but T. urticae entered diapause earlier than E. carpini borealis and N. fallacis. Densities of N. fallacis increased with increase in spider mite densities. However, the numerical response of the predator was more evident for T. urticae than for E. carpini borealis. Nevertheless, the predator was spatially associated with the two prey species. The spatial and seasonal distribution of N. fallacis in relationship to host plant phenology and prey distribution may influence the effectiveness of this predator as a biological control agent against spider mites in red raspberry. Densities of the predator increased too late to prevent spider mite damage. The predatory role of N. fallacis could be enhanced by introducing or conserving predators that are more tolerant to climatic factors that prevail in and around the cane canopy in the beginning of the season.

Host plant-mediated interactions between Tetranychus urticae and Eotetranychus carpini borealis (Acari: Tetranychidae).

Competitive interactions between Tetranychus urticae and Eotetranychus carpini borealis were investigated under laboratory and greenhouse conditions. When placed first to colonize red raspberry leaves, T. urticae caused extinction of E. carpini borealis populations. E. carpini borealis had detrimental effects on T. urticae but did not cause T. urticae population extinction. The area used by E. carpini borealis for egg deposition decreased with an increase in the number of T. urticae eggs. Red raspberry showed an induced response to T. urticae and E. carpini borealis feeding after two weeks of infestation. Population growth of each species was reduced on plants that were previously infested by conspecifics but inducible response by one species had no effects on the other species.

Oxygen detoxifying enzymes in parasites: a review.

This review focuses on parasite enzymes which are involved in the detoxification of oxygen radicals, and covers the following enzymes: superoxide dismutase, catalase, glutathione peroxidase, glutathione-S-transferase and glutathione reductase. These enzymes are crucial for parasites to evade oxygen-mediated attack by host leukocytes, both intracellularly and extracellularly. In addition, the newly defined parasite system involving trypanothione, trypanothione peroxidase and trypanothione reductase is discussed.

Reproductive potential: its influence on the susceptibility of a species to pesticides.

Acute lethal concentration estimates (72-hr LC50) and population growth rates (7-day instantaneous rate of increase) of two mite species, an herbivore, the two-spotted spider mite Tetranychus urticae Koch, and the generalist predator mite Iphiseius degenerans Berlese, were developed after exposure to two pesticides, dicofol and Neemix. For each pesticide, LC50 estimates for both species were similar, yet the two species exhibited completely different susceptibility when population growth rate was the endpoint evaluated; I. degenerans was much more susceptible than T. urticae to either pesticide. For example, populations of I. degenerans became extinct after exposure to 250-ppm azadirachtin, the active ingredient in Neemix, while T. urticae populations became extinct after exposure to 1000 ppm. A similar relationship was found for dicofol. The no observable effect concentration (NOEC) for population growth rates after Neemix exposure was 4 ppm for I. degenerans and 125 ppm for T. urticae. These NOEC values were equivalent to the acute LC2 for the immature stage of I. degenerans and the acute LC65 for the immature stage of T. urticae. Consequently, populations of T. urticae were able to compensate for high losses of individuals while I. degenerans populations could not compensate for losses. An analysis of reproduction data indicated that unexposed T. urticae produced four to five times more offspring than I. degenerans. This in itself was important because it indicated that I. degenerans was intrinsically more susceptible than T. urticae because similar effects on reproduction would be more devastating to the species with a lower reproductive rate. Results indicate that a species' reproductive potential can greatly influence its susceptibility to toxicants.

Purine nucleoside phosphorylase of the malarial parasite, Plasmodium lophurae.

Purine nucleoside phosphorylase (EC 2.4.2.1, purine nucleoside:orthophosphate ribosyltransferase) was purified and characterized from the malarial parasite, Plasmodium lophurae, using a chromatofocusing (Pharmacia) column and a formycin B affinity column. The apparent isoelectric point of the native protein, as determined by chromatofocusing, was 6.80. By gel filtration and both native and sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the native enzyme appeared to be a pentamer with a native molecular weight of 125,300 and a subunit molecular weight of 23,900. The enzyme had a broad pH optimum, pH 5.5-7.5, with maximum activity at pH 6.0-6.5. The enzyme reaction was readily reversible with a Km for inosine of 33 microM and a Km for hypoxanthine of 82 microM. Thioinosine, guanosine, and guanine were also substrates for the plasmodial enzyme, but allopurinol and adenine were not. The parasite enzyme was competitively inhibited by formycin B (Ki = 0.39 microM). Formycin A, azaguanine, and 8-aminoguanosine were not inhibitors of the enzyme.