David A. Raworth

Determining numbers of active carabid beetles per unit area from pitfall-trap data

Movement of Pterostichus melanarius (Illiger) (Coleoptera: Carabidae) was studied in the laboratory, and a simulation model developed. The model was calibrated and validated using mark‐release‐recapture within a grid of pitfall traps in a commercial raspberry field. Rate of movement increased linearly with both temperature and starvation. The temperature threshold for movement, pooling all starvation levels was 3.8 °C ± 0.78 (s.e.). When beetles were released at various distances from a trap in the simulation model, the probability of capture during one day was about 0.13 at a release distance of 10 cm and fell rapidly with distance and temperature. At 5, 10, 15, and 20 °C, the maximum radius sampled by a trap in one day was about 8, 17, 24, and 29 m, respectively. Density was linearly related to catch, but the slope of the line and the variance of the density estimate increased rapidly at lower temperatures. Equations for determining density per m2 (±s.d.) were developed from the model, incorporating temperature, number of beetles caught per trap, and number of traps.

(2R, 7S)-diacetoxytridecane: Sex pheromone of the aphidophagous gall midge, Aphidoletes aphidimyza

In a recent study, evidence was presented that females of the aphidophagous midge Aphidoletes aphidimyza (Rondi) (Diptera: Cecidomyiidae) release a sex pheromone to attract mates. Our objectives were to identify and bioassay the pheromone. Coupled gas chromatographic–electroantenno- graphicDetection (GC-EAD) analyses of untreated and hydrogenated pheromone extract on three fused-silica columns (DB-5, DB-23, DB-210) revealed a single compound that elicited responses from male antennae. Retention index calculations of this candidate pheromone (CP) suggested that it was a di-acetate. Considering that most of the presently identified cecidomyiid pheromones consist of a 13-carbon chain with (at least) one acetate group in C2, we synthesized 2,6-, 2,7-, 2,8-, 2,9-, 2,10-, 2,11-, and 2,12-diacetoxytridecane. In GC analyses of these compounds, only 2,7-diacetoxytridecane cochomatographed with CP on all columns. In laboratory two-choice experiments with stereospecifically synthesized stereoisomers, only (2R,7S)-diacetoxytridecane elicited significant anemotatic responses by male A.aphidimyza. In trapping experiments in greenhouse compartments, only traps baited with (2R,7S)-diacetoxytridecane captured significant numbers of male A. aphidimyza, clearly revealing the absolute configuration of the pheromone. Failure of the stereoisomeric mixture (containing all four stereoisomers including the pheromone) to attract males is due to inhibitory characteristics of the (2R,7R)- and (2S,7R)-stereoisomers. The pheromone of zoophagous A. aphidimyza resembles those from phytophagous cecidomyiid midges, suggesting a common, diet-independent pathway for pheromone biosyntheses.

Olfactory response by the aphidophagous gall midge, Aphidoletes aphidimyza to honeydew from green peach aphid, Myzus persicae

Female adults of the aphidopagous gall midge, Aphidoletes aphidimyza (Rondani) (Diptera: Cecidomyiidae), showed an olfactory response to honeydew excreted by the green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae) under laboratory conditions. The response was only elicited by treatments with honeydew, whereas aphids, aphids with pepper plants or leaves, and pepper plants or leaves were not attractive to the midges. Dose‐dependent responses were observed from whole honeydew, honeydew volatiles extracted in pentane, and honeydew volatiles captured on Porapak Q®. When honeydew was eluted with three sequential pentane washes, a positive response was only observed from the midges for the first wash. Female midges laid more eggs on pepper plants infested with higher densities of M. persicae. The olfactory response of midges to honeydew is discussed with respect to prey location.

Control of Two-spotted Spider Mite by Phytoseiulus persimilis

Abstract Two-spotted spider mites, Tetranychus urticae Koch have been a problem for many years. A broad approach to population management is needed. – Hybridization between greenhouse strains of T. urticae and introduced strains may result in a strain with different life-history traits. Life-history traits of mites in greenhouses should be regularly monitored to provide an historical data base, and input for simulation models. – Phytoseiulus persimilis Athias-Henriot operates well within certain ecological limits. A predator community approach may be useful when conditions are not suitable for P. persimilis. – After 30 years of mass rearing, the development rate of P. persimilis has not changed, but fecundity appears to be reduced, largely as a result of reduced reproductive period. – Insectaries have attempted to set quality standards, but many factors can affect P. persimilis and tests must be developed for rapid assessment of quality at the greenhouse. – More work is needed to develop and implement rapid sampling protocols with acceptable precision and accuracy. – Digital data acquisition and management systems will be necessary, to summarize data spatially and temporally, provide input for simulation models, and provide a data base for research analyses. – Simple simulation models, although inaccurate, may be useful in answering specific pest management questions.

Primary and Secondary Parasitoids (Hymenoptera) of Aphids (Hemiptera: Aphididae) on Blueberry and Other Vaccinium in the Pacific Northwest

Abstract 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 °C, summing from 1 January, may effectively augment the natural spring populations by creating overlapping generations.

Polymorphic fundatrices in thimbleberry aphid — ecology and maintenance

The thimbleberry aphid,Masonaphis maxima (Mason) lives on patches of plants that support 3,4 or 5 generations depending on site and weather. The life cycle requires sexual females and males to produce overwintering eggs. The eggs hatch in the spring to produce the first ’fundatrix’ generation; subsequent generations are produced parthenogenically. Males and other morphs are produced by wingless virginoparae, but sexual females are produced by ’gynoparae’, a winged morph that is specialized to produce only sexual females. The fundatrices have no indication of the number of generations that the plants will support in the current year. There are two fundatrix types that coexist in different ratios depending on the number of generations supported by the patch the previous year. One type produces sexual females in generations 3 and 5, and males in generations 4 and 5; the other type produces sexual females in generations 4 and 5, and males in generations 3, 4 and 5. The dimorphism adapts the aphid to its heterogeneous and somewhat unpredictable environment. The role of sex in the maintenance of the dimorphism is discussed. This is the first report of fundatrix polymorphism and consequent differential sex expression in aphids.