Aphid Parasitism Research Articles

Enhancing parasitism of wheat aphids through apparent competition: a tool for biological control

As cereal aphids are only present during 2–3 months per year in cereal crops, their parasitoids rely on alternative hosts to complete their life cycle. These parasitoids often have the same aphid hosts, which leads to apparent competition. Development on alternative host may increase parasitoid abundance and consequently increase their pressure on cereal aphids. Intensive agriculture frequently reduces the availability of non-crop habitats where alternative aphids may be present. The apparent competition hypothesis was examined in two traditional wheat plots compared to two other plots, with strips of alternative host aphids on leguminosae (red clover and alfalfa) and graminae (ryegrass and meadow fescue). In June/July, parasitism on wheat aphids ( Metopolophium dirhodum, Sitobion avenae, and Rhopalosiphum padi) was higher in 1998 than in 1997, in all the plots studied. During summer 1998, significantly more parasitised wheat aphids were found in strip-designed plots than in the controls, and this higher parasitism rate was positively correlated to a higher parasitoid activity during May, due to the presence of alternative hosts. The interaction between wheat aphids in summer and aphids in the strips in spring is an example of apparent competition, mediated by shared parasitoids. Alternative hosts allow parasitoids to increase their numbers and consequently to apply a higher pressure on aphids in wheat crops.

Biodiversity and biocontrol: emergent impacts of a multi‐enemy assemblage on pest suppression and crop yield in an agroecosystem

AbstractThe suppression of agricultural pests has often been proposed as an important service of natural enemy diversity, but few experiments have tested this assertion. In this study we present empirical evidence that increasing the richness of a particular guild of natural enemies can reduce the density of a widespread group of herbivorous pests and, in turn, increase the yield of an economically important crop. We performed an experiment in large field enclosures where we manipulated the presence/absence of three of the most important natural enemies (the coccinellid beetle Harmonia axyridis, the damsel bug Nabis sp., and the parasitic wasp Aphidius ervi) of pea aphids (Acyrthosiphon pisum) that feed on alfalfa (Medicago sativa). When all three enemy species were together, the population density of the pea aphid was suppressed more than could be predicted from the summed impact of each enemy species alone. As crop yield was negatively related to pea aphid density, there was a concomitant non‐additive increase in the production of alfalfa in enclosures containing the more diverse enemy guild. This trophic cascade appeared to be influenced by an indirect interaction involving a second herbivore inhabiting the system – the cowpea aphid, Aphis craccivora. Data suggest that high relative densities of cowpea aphids inhibited parasitism of pea aphids by the specialist parasitoid, A. ervi. Therefore, when natural enemies were together and densities of cowpea aphids were reduced by generalist predators, parasitism of pea aphids increased. This interaction modification is similar to other types of indirect interactions among enemy species (e.g. predator–predator facilitation) that can enhance the suppression of agricultural pests. Results of our study, and those of others performed in agroecosystems, complement the broader debate over how biodiversity influences ecosystem functioning by specifically focusing on systems that produce goods of immediate relevance to human society.

Development of a Sampling Plan in Winter Wheat that Estimates Cereal Aphid Parasitism Levels and Predicts Population Suppression

From 1998 to 2001, the relationship between the proportion of tillers with >0 mummified aphids (Ptm) and the proportion of cereal aphids parasitized (Pp) was estimated on 57 occasions in fields of hard red winter wheat located in central and western Oklahoma. Both original (57 fields) and validation data (34 fields; 2001–2002) revealed weak relationships between Ptm and Pp, however, when Ptm > 0.1, Pp always exceeded the recommended parasitism natural enemy threshold of 0.2. Based on the relationship between Ptm and Pp, upper (Ptm1) and lower (Ptm0) decision threshold proportions were set at 0.1 and 0.02, respectively. We monitored cereal aphid populations in 16–25 winter wheat fields over time, and based on the upper and lower decision threshold proportions (Ptm1 = 0.1, Ptm0 = 0.02), predicted whether aphid intensities (# per tiller) would increase above or be maintained below selected economic thresholds (3, 9, and 15 aphids per tiller). Results of this validation study revealed that aphid intensity exceeded an economic threshold in only one field when predicted to remain below Ptm > 0.1, but aphid intensity reached a maximum of only four aphids per tiller. The sampling plan developed during this study allowed us to quickly classify Ptm, and independent of initial cereal aphid intensities, very accurately predict suppression of populations by parasitoids. Sequential sampling stop lines based on sequential probability ratio tests for classifying proportions were calculated for Ptm1 = 0.1 and Ptm0 = 0.02. A minimum of 26 tiller samples are required to classify Ptm as above 0.1 or below 0.02. Based on the results of this study, we believe that simultaneous use of aphid and parasitoid sampling plans will be efficient and useful tools for consultants and producers in the southern plains and decrease the number of unnecessary insecticide applications.

Development of a sampling plan in winter wheat that estimates cereal aphid parasitism levels and predicts population suppression.

From 1998 to 2001, the relationship between the proportion of tillers with >0 mummified aphids (Ptm) and the proportion of cereal aphids parasitized (Pp) was estimated on 57 occasions in fields of hard red winter wheat located in central and western Oklahoma. Both original (57 fields) and validation data (34 fields; 2001-2002) revealed weak relationships between Ptm and Pp, however, when Ptm > 0.1, Pp always exceeded the recommended parasitism natural enemy threshold of 0.2. Based on the relationship between Ptm and Pp, upper (Ptm1) and lower (Ptm0) decision threshold proportions were set at 0.1 and 0.02, respectively. We monitored cereal aphid populations in 16-25 winter wheat fields over time, and based on the upper and lower decision threshold proportions (Ptm1 = 0.1, Ptm0 = 0.02), predicted whether aphid intensities (# per tiller) would increase above or be maintained below selected economic thresholds (3, 9, and 15 aphids per tiller). Results of this validation study revealed that aphid intensity exceeded an economic threshold in only one field when predicted to remain below Ptm > 0.1, but aphid intensity reached a maximum of only four aphids per tiller. The sampling plan developed during this study allowed us to quickly classify Ptm, and independent of initial cereal aphid intensities, very accurately predict suppression of populations by parasitoids. Sequential sampling stop lines based on sequential probability ratio tests for classifying proportions were calculated for Ptm1 = 0.1 and Ptm0 = 0.02. A minimum of 26 tiller samples are required to classify Ptm as above 0.1 or below 0.02. Based on the results of this study, we believe that simultaneous use of aphid and parasitoid sampling plans will be efficient and useful tools for consultants and producers in the southern plains and decrease the number of unnecessary insecticide applications.

Composition of the volatiles from intact and tea aphid‐damaged tea shoots and their allurement to several natural enemies of the tea aphid

Abstract: The comparison between the composition of the volatiles from intact tea shoots (ITS) and that from tea aphid‐damaged tea shoots (TADTS) was accomplished, and the difference of both volatiles in attraction to natural enemies of the tea aphid, Toxoptera aurantii, i.e the ladybug, Leis axyridis (Pallas), the aphid parasite, Aphidius sp., and the lacewing, Chrysopa septempunctata Wesmeal, was investigated in the current paper. Volatile components from ITS, obtained by air entrainment, were identified by their mass spectra and retention times and comfirmed by comparison with authentic samples. They are E‐2‐hexenal, ocimene, Z‐3‐hexenyl acetate, Z‐3‐hexen‐1‐ol, butanoic acid‐3‐hexenyl ester, linalool, 1‐octanol, geraniol and indole. Volatiles from TADTS have been identified as E‐2‐hexenal, ocimene, Z‐3‐hexenyl acetate, Z‐3‐hexen‐1‐ol, linalool, geraniol, indole, benzaldehyde and E‐2‐hexenoic acid. Z‐3‐hexen‐1‐ol is the main component in the two kinds of volatiles, whilst benzaldehyde is the another main component in TADTS volatiles. The air entrainment extracts of TADTS and benzaldehyde elicit the stronger electroantennogram (EAG) responses, and the stronger upwind flight and arresting behaviour from each natural enemy in wind tunnel. EAG responses from Leis axyridis and Chrysopa septempunctata were bigger than those from Aphidius sp., whereas Leis axyridis responds to these odours slightly less than Aphidius sp. and Chrysopa septempunctata in wind tunnel bioassay. So TADTS emits volatile synomones, in which the amount of benzaldehyde is ample and its allurement is the strongest.

Pea aphid clonal resistance to the endophagous parasitoid Aphidius ervi

The physiological mechanism of resistance to the endophagous braconid Aphidius ervi Haliday (Hymenoptera, Braconidae) by a pink clone (PC) of Acyrthosiphon pisum (Harris) (Homoptera, Aphididae) has been investigated. Comparative data on parasitoid development and associated host biochemical changes in the resistant PC aphids and in a susceptible green clone (GC) of A. pisum are reported. When the PC aphids were attacked as early 4th instars, the developing parasitoid larvae showed a strongly reduced increase in size, compared to those synchronously developing in GC aphids, and were unable to produce a regular mummy. In contrast, parasitism of 2nd instar PC aphids, allowed completion of parasitoid development, but adults had a prolonged developmental time, due to a longer duration of parasitoid’s final (3rd) instar. In all cases, teratocytes, cells deriving from the A. ervi serosal membrane, and the proteins abundantly synthesised by them, were never found in the haemolymph of parasitised PC aphids. Host castration, as demonstrated by total protein incorporation into reproductive tissues, was total in the majority of early (2nd instar) parasitised host aphids, while it was limited when later instars (4th) of PC aphids were parasitised. This is partly due to the absence of the cytolytic activity of teratocytes on host embryos, which, through their persistence, may compete for nutritional resources with the developing parasitoid larvae. In parasitised PC aphids, this competitive effect is further aggravated for the parasitoid by the absence of the regulated amino acid titre increase in the host haemolymph, which is regularly observed in GC aphids. Failure of teratocyte development in the PC clone of the pea aphid is, then, the major functional constraint accounting for the reduction/inhibition of A. ervi larval growth. The reported results allow to assess in vivo the role of teratocytes in the host physiological redirection and nutritional exploitation by the parasitoid, and to integrate and validate the proposed physiological model of host-parasitoid interactions in the system A. pisum-A.ervi.

Patch and prey utilization behaviors by Aphelinus albipodus and Diaeretiella rapae (Hymenoptera: Aphelinidae and Aphidiidae) on Russian wheat aphid (Homoptera: Aphididae)

Abstract The patch and host utilization behaviors of the parasitoids Diaeretiella rapae (Kurdjumov) and Aphelinus albipodus (Hayat and Fatima) in relation to the Russian wheat aphid, Diuraphis noxia (Mordvilko), were examined on wheat plants. Individual female parasitoids were observed for 1 h after arriving on a wheat plant with varying D. noxia densities. The total amount of time spent on the leaf and the number of occasions a parasitoid left the leaf were dependent on aphid densities for D. rapae . In contrast, A. albipodus remained on a plant for almost the entire hour irrespective of aphid densities. After 1 h on the wheat plants, single D. rapae females produced up to 31 progeny from 40 aphids, while single A. albipodus produced a maximum of six progeny. These results can be explained by the differences between the parasitoids in prey handling times, searching, and host feeding behaviors, and parasitoid physiology. The mean oviposition time for A. albipodus was 119 s compared to 1 or 2 s for D. rapae . The time between attacks was also much greater for A. albipodus at all prey densities, partially a result of this parasitoid feeding on aphids. Our results agree with the observation that A. albipodus has many fewer eggs ready for oviposition compared to D. rapae . Therefore, it is not surprising that A. albipodus remained for extended periods on wheat plants with many aphids, allowing development of additional eggs and parasitization of more aphids. The patch and prey utilization rates by A. albipodus seem likely to limit its rate of spatial spread during a growing season relative to D. rapae .

Lysiphlebus Förster (Hymenoptera: Braconidae: Aphidiinae) in Australia

AbstractRecords are provided of the aphidiine parasites of aphids, Lysiphlebus fabarum (Marshall) and L. testaceipes (Cresson), parasitizing species of Aphis Linnaeus, Rhopalosiphum Koch and Toxoptera Koch in eastern Australia. Both species of Lysiphlebus were imported into Australia in 1982 for purposes of biological control, evidently with little or no initial success. Lysiphlebus testaceipes, however, has been reared in abundance in eastern Australia since 1997. A brief account is given of the history of the parasites in Australia and the possible provenance of recently collected material is discussed. Characters to distinguish between the two species are provided.

Spatially aggregated parasitism on pea aphids, Acyrthosiphon pisum , caused by random foraging behavior of the parasitoid Aphidius ervi

We investigated the role of the foraging,behavior of the parasitoid wasp Aphidius erui in producing nonrandom spatial patterns of parasitism among pea aphids, Acyrthosiphon pisum. We measured spatial variability in percent parasitism by determining the number of aphids and percent parasitism in 40 sampling plots (0.65-m 2 circles) located within a homogeneous alfalfa field. In one replicate of this experiment, mean parasitism of aphids was 18.7%, and percent parasitism showed density-independent aggregation (i.e., greater than random variability in percent parasitism among sampling plots). In the other replicate, mean parasitism was 56.3%, and percent parasitism was not aggregated among plots. We used a combination of field observations of parasitoid foraging and mathematical models to explore these results. In particular, we asked whether the presence or absence of density-independent aggregation at different mean percent parasitism can be explained even if parasitoids forage randomly, without changing their behavior in response to encounters with aphids. Observations show that parasitoids tend to move short distances between nearby alfalfa stems (mean = 10.8 cm), and the turning angle between successively visited stems was uniformly distributed. We incorporated this behavior into both simulation and analytical models of parasitoid foraging. The models show the same pattern as that observed in the field: parasitism is aggregated in a density-independent fashion when mean percent parasitism is low but not when mean percent parasitism is high. Therefore, density-independent aggregation in percent parasitism does not necessarily imply behavioral responses of parasitoids to host encounters and previously parasitized hosts.

Specific Ribosomal DNA Marker for Early Polymerase Chain Reaction Detection of <I>Aphelinus hordei</I> (Hymenoptera: Aphelinidae) and <I>Aphidius colemani</I> (Hymenoptera: Aphidiidae) from <I>Diuraphis noxia</I> (Homoptera: Aphididae)

Abstract To monitor aphid parasitism by Aphelinus hordei (Kurdjumov) and Aphidius colemani Viereck, we developed specific ribosomal DNA markers to distinguish them from several other cereal aphid parasitoid species and two important host species, the Russian wheat aphid, Diuraphis noxia (Mordvilko), and the greenbug, Schizaphis graminum (Rondani). Ribosomal DNA sequences for the internal transcribed spacer 2 (ITS2) were first cloned and sequenced from A. hordei, A. albipodus Hayat & Fatima, A. asychis Walker, A. varipes (Foerster), A. colemani, D. noxia, and S. graminum. We designed specific primers based on the ITS2 sequences. Polymerase chain reaction (PCR) amplification of wasp and aphid DNA using these primers, followed by agarose gel electrophoresis, successfully distinguishes A. hordei and A. colemani from all three other Aphelinus species and two aphid species. A 411-bp nucleotide fragment and a 571-bp fragment were amplified only from A. hordei and from A. colemani, respectively, and no such fragm...

Effects of wheat foliar fungicides on the aphid endoparasitoid Aphidius rhopalosiphi DeStefani‐Perez (Hym., Aphidiidae) on glass plates and on plants

Abstract: The side‐effects of several fungicides used in wheat to control disease at heading growth stage were assessed on the aphid parasitoid Aphidius rhopalosiphi by tests conducted in the laboratory on glass plates and in the greenhouse on young wheat plants. Very few formulations containing only one active ingredient (carbendazim, cyproconazole or epoxyconazole) or combinations of two (carbendazim + cyproconazole, carbendazim + hexaconazole) were harmless to A. rhopalosiphi in the glass‐plate tests. There was no apparent synergism between fungicides tested in combinations. The parasitoid mortalities in tests carried out on plants were less and chlorothalonil, epoxyconazole, fenpropidin, fenpropimorph, flusilazole, flutriafol, prochloraz, tebuconazole, tridemorph and a number of combinations (carbendazim + flutriafol, chlorothalonil + cyproconazole, epoxyconazole + tridemorph, chlorothalonil + hexaconazole, chlorothalonil + flutriafol, cyproconazole + prochloraz, epoxyconazole + fenpropimorph, fenpropimorph + propiconazole, propiconazole + tridemorph, triadimenol + tridemorph) were harmless or only slightly harmful to the aphid parasitoid. Several combinations (carbendazim + epoxyconazole, carbendazim + fenpropimorph, carbendazim + flusilazole, carbendazim + tebuconazole, chlorothalonil + fenpropimorph, chlorothalonil + flusilazole, fenpropimorph + fenpropidin, fenpropimorph + prochloraz, fenpropidin + propiconazole, fenpropidin + tebuco nazole, tebuconazole + triadimenol) were toxic for wasps on plants. The parasitoid mortalities were less on plants than on glass plates but the wasps spent less time on treated leaves and in some cases parasitism of aphids was reduced to a large extent. These results suggest that in addition to study of the direct effects of pesticides on beneficial insects (mortalities, reduction of fertility) their effects on the behaviour of the insects should also be studied. Products that induced a repellent effect need further testing in field or semi‐field conditions. However, many fungicide combinations that have little or no effect on A. rhopalosiphi can protect wheat against a wide range of diseases and the results obtained in this study indicate that an appropriate and effective protection of wheat at earing growth stage can be achieved with products that have no effects on aphid parasitoids.

Effectiveness of aphid parasitoids (Hymenoptera: Aphidiidae) on winter wheat in two agricultural systems

From the obtained results we can note that the parasitoids in our experiments in 1 997 and 1998 had considerable influence on decline of aphids population density, at which the percent of parasitization in milk maturity stage of wheat was from 2.7 to 35%. The culmination of parasitization was recorded in our experiments about 7–10 days after the culmination of population density of aphids. The obtained results did not confirm the definite influence of different growing systems on parasitization of aphids, because in 1997 the parasitization was very high in integrated growing system and in 1998 in ecological growing system. The influence of different growing systems on aphids parasitization appeared during a given year and within an growing system. It also appeared between different years and it was found that these differences were significant. The parasitoids found were: Aphidius ervi Haliday, A. rlwpalosiphi De Stefani-Pcrcz, A. uzbekistanicus Luzhctzki, Praon volucre (Hal iday), Ephedrus plagialor (Nees), Diaeretiefla rapae (M'lntosh). In 1997, the most abundant species were Aphidius ervi and A. rhopafosiphi and in 1998 A. ubekistanicus and Aphidius ervi.

Increased Parasitization of Aphids on Trap Plants Alongside Vials Releasing Synthetic Aphid Sex Pheromone and Effective Range of the Pheromone

Aphid-infested cereal trap plants were used to detect the effects of aphid sex pheromone components on aphid parasitoid activity in arable field margins. The presence of aphid sex pheromones significantly increased parasitization levels by aphid parasitoids on the plants. By placing plants alongside and at varying distances away from a pheromone-releasing vial, the technique was used to measure the distance over which a point source of aphid sex pheromone could increase parasitization levels. Pheromone-releasing vials significantly increased parasitization by the generalist parasitoid Praon volucre on plants adjacent to vials and on plants placed 20 cm away. When the distance between pheromone-releasing vials and aphid-infested plants was increased to 1 m, parasitization by P. volucre was increased only on the plant adjacent to the vial, whereas parasitization by the specialist parasitoid Aphidius rhopalosiphi was also increased on plants placed 1 m away. This indicates a possible difference between the parasitoids in their foraging behaviour in response to semiochemical cues during host selection. When the experiment was repeated with some trap plants placed 3 m away from the pheromone-releasing vial, parasitization was again concentrated on plants directly alongside the vial, but only P. volucre appeared to be active in the field at the time of this experiment, so the effect on A. rhopalosiphi could not be assessed. The results are encouraging for the prospects of using aphid sex pheromones to manipulate parasitoids in order to improve aphid population control.

Hazelnut Production in Oregon

Hazelnuts in Oregon are grown on 30,000 acres by ≈1000 orchardists in the Willamette Valley. Their annual production accounts for 3% to 5% of the world's hazelnut tonnage. The trees are grown in a single trunk system wrtb an average spacing of 20 feet between trees. Mechanical harvestihg is done in October. The industry employs an Integrated Pest Management approach, utilizing combinations of scouting, trapping, and biological control. The main insect pests are filbertworm, filbert leafroller, obliquebanded leafroller, and filbert aphids. The aphid parasite Trioxys pallidus was imported from Europe and successfully established in Oregon. Eastern Filbert Blight, Anisogramma anomala, a fungus disease, is the most serious disease problem in the industry. Annual applications of nitrogen to the soil and boron applied to the foliage are routine for Oregon's hazelnut growers. OSU research has quantified the importance of good light distribution in the tree canopy for increased nut production. OSU recommends a 5-year rotational pruning program. Some growers use mechanical hedging instead of hand pruning. OSU is home to the world's largest hazelnut breeding program. `Barcelona' is still the main, cultivar grown, while `Ennis' is the main in-shell variety. There is growing interest in planting varieties with a high percent kernel, such as `Casina', `Willamette', and `Lewis'.

Paratrombium welbourni sp. nov. (Acari: Trombidiidae), an ectoparasite of aphids {Homoptera: Aphididae) in Spain

Abstract Paratrombium welbourni Goldarazena & Zhang sp. nov. (Acari: Trombidiidae) is described from a larva parasitic on Aphis sp. (Homoptera: Aphididae) from Navarra-Nafarroa (Spain). This is the first record of Paratrombium larvae as parasites of aphids. Known host records of Paratrombium larvae are reviewed.

Paratrombium welbourni sp. nov. (Acari: Trombidiidae), an ectoparasite of aphids {Homoptera: Aphididae) in Spain

Paratrombium welbourni Qoldarazena & Zhang sp. nov. (Acari: Trombidiidae) is described from a larva parasitic on Aphis sp. (Homoptera: Aphididae) from Navarra-Nafarroa (Spain). This is the first record of Paratrombium larvae as parasites of aphids. Known host records of Paratrombium larvae are reviewed.

Activité saisonnière et distribution des parasitoïdes de pucerons du froment d’hiver

Activity of antagonists in winter and early spring as well as in late summer and autumn plays an important role in the control of cereal aphid populations. Indeed, parasitoids active early in the year are important to avoid high aphid densities. Late summer and autumn correspond to the transition period between two wheat cultures, and parasitoid activity would thus reduce aphid infestation. During these critical periods, other crops like rye-grass and red clover containing alternative hosts could play the role of parasitoid reservoirs. During 1996, parasitoid activity was measured by trap planting in wheat, rye-grass, red clover and fallow grassland. In each plot, early spring was characterized by an important parasitoid activity, while aphids remained at a low level. Later in spring, activity decreased, and aphid development began even during this period. During the summer, when aphids reached their population peak, parasitoid activity rose again. Percentage of parasitism of aphids sampled was only important during summer in red clover and rye-grass. In wheat and fallow grassland, percentage of parasitism remained at a low level. The role of synchronization between parasitoid activity and aphid development is discussed.

Effects of honeydew and insecticide residues on the distribution of foraging aphid parasitoids under glasshouse and field conditions

AbstractThe opposing effects of attraction to host‐derived kairomones and repellency from the pyrethroid insecticide deltamethrin were investigated with aphid parasitoids from the genus Aphidius (Hymenoptera: Aphidiinae). The spatial distribution of female parasitoids was recorded in a series of experiments conducted in a small glasshouse containing wheat plants either infested with cereal aphids, Sitobion avenae (F.) (Homoptera: Aphididae), uninfested or treated with the recommended field concentration of deltamethrin. The number of parasitoids per plant were counted at 0.5 h, 1 h and then at one hourly intervals up to 8 h after release. Parasitoids showed a strong aggregation response to aphid‐infested plants compared to adjacent uninfested plants. With the introduction of insecticide‐treated plants around the aphid‐infested plants, parasitoids showed a greater tendency to disperse away, resulting in fewer parasitoids on plants and significantly lower rates of aphid parasitism. The degree of aphid fall‐off from plants was a good indicator of parasitoid foraging activity. In field studies, using sticky traps to measure the activity of parasitoids in plots sprayed with water, deltamethrin and/or an artificial honeydew solution, repellent properties were evident for up to 2 days after application. The attraction/arrestment stimuli associated with the honeydew solution were sufficient for parasitoids to continue searching insecticide‐treated areas. The implications of these findings for parasitoids searching crops contaminated with aphid‐derived kairomones and insecticides are discussed.

Alternative Production and Protection Practices for Hazelnuts

Oregon's Willamette Valley is home to 99% of the U.S. domestic production of hazelnuts, Corylus avellana. There are currently around 30,000 acres of hazelnuts in Oregon. Hazelnuts are a relatively low resource input crop when compared to other orchard crops. They require few pesticide applications, and are harvested mechanically. Oregon State Univ. (OSU) developed an Integrated Pest Management (IPM) program for hazelnuts in the middle 1980s that is widely adopted in the industry today. Sampling schemes and action thresholds have been developed for the filbertworm (the most important insect pest), as well as: obliquebanded leafroller, filbert leafroller, and filbert aphids. In an example of classical biological control, a filbert aphid parasite, Trioxysis pallidus, was imported from Europe in 1984. Trioxysis has successfully established itself throughout the industry. As a result, the need for aphid control sprays has been significantly reduced. Current research in hazelnut IPM is focused on a “soft pesticide” program that features an insect growth regulator for filbertworm control. Recent research with isotopically labeled nitrogen seeks to improve the efficiency of nitrogen fertilization in the industry. The northern portion of the industry is affected by Eastern Filbert Blight. OSU research has secured registrations of effective fungicides and refined the control program for the blight. Work is being completed on a predictive model to quantify the extent of spore dispersal, based on accumulated rainfall.

Parasitism of aphids (Homoptera: Aphididae) by larvae of Al/othrombium pu/vinum (Acari: Trombidiidae): Host species selection, host size selection, and superparasitism

Abstract Three aspects of aphid host selection by parasitic larvae of Allothrombium pulvinum Ewing (Acari: Trombidiidae) were examined using two-choice tests in the laboratory. Seven aphid species were studied for host selection by larval mites: Cryptomyzus alboapicalis (Theobald), Liosomaphis berberidis (Kaltenbach), Macrosiphum rosae L., Myzus ornatus Laing, Myzus persicae (Sulzer), Periphyllus testudinaceus (Fernie), and Dreoanosiphum platanoidis (Schrank). In host species selection tests, larval mites preferred M. persicae to M. ornatus, which was as attractive to the mite parasites as M. rosae. Larval mites preferred M. rosae to C. alboapicalis. Aphidinae as represented by M. persicae, M. rosae or C. alboapicalis was more preferable to the mite parasites than P. testudinaceus of the Chaitophorinae, which was as attractive as D. platanoidis of the Drepanosiphinae. In host size selection tests, significantly more mites selected the large host than small host of L. berberidis and D. platanoides. The lar...