Entomopathogenic nematodes for control of diapausing codling moth (Lepidoptera: Tortricidae) in fruit bins

Fruit bins infested with diapausing larvae of codling moth larvae, Cydia pomonella (L.), are a source of reinfestation of orchards and may jeopardize the success of mating disruption programs and other control strategies. Bins are not routinely treated for control of overwintering codling moth before placing them in orchards. Entomopathogenic nematodes provide a noninsecticidal alternative to methyl bromide that could be applied at the time bins are submerged in dump tanks at the packing house for flotation of fruit. Diapausing codling moth larvae in miniature fruit bins were highly susceptible to infective juveniles of Steinernema carpocapsae (Weiser). Immersion of bins in suspensions of S. carpocapsae ranging from 5 to 100 infective juveniles per milliliter of water resulted in 68-100% mortality. Immersion times of 1 or 5 min in suspensions with 5 infective juveniles of S. carpocapsae per milliliter of water, with and without Tween 80 (0.01%), yielded essentially the same mortality of codling moth larvae. Highest mortalities in codling moth larvae (88%) after treatment of bins in suspensions of 5 infective juveniles of S. carpocapsae per milliliter of water were observed after incubation for 24 h at 25 degrees C and 70% RH. Lowest mortalities (37%) were observed after incubation at 15 degrees C and 35% RH. Comparative tests conducted with Heterorhabditis marelatus Liu & Berry, Steinernema kraussei (Steiner), and S. carpocapsae with 5 infective juveniles per milliliter of water resulted in 21.7, 53.9, and 68.7% mortality, respectively. The use of miniature fruit bins as described in this article provides an effective means of assessing nematode efficacy without the cumbersome size of commercial bins.     

病原线虫对桔小实蝇种群的控制作用

通过室内和田间实验研究了昆虫病原线虫对桔小实蝇Bactrocera (Bactrocera) dorsalis (Hendel)的控制作用。室内实验结果表明,供试的3种线虫的4个品系（小卷蛾斯氏线虫Steinernema carpocapsae All品系与A24品系,夜蛾斯氏线虫Steinernema feltiae SN品系和嗜菌异小杆线虫Heterorhabditis bacteriophora H06品系）,以小卷蛾斯氏线虫All品系对桔小实蝇的侵染力最强,其3天的LD₅₀和LD₉₅分别为35.0和257.1条/cm²土壤。按300条/cm²土壤的量施用,小卷蛾斯氏线虫All品系对当代桔小实蝇的控制效果为86.3%。用以虫期作用因子组建的生命表方法评价了小卷蛾斯氏线虫All品系对田间桔小实蝇下代种群的控制作用,结果表明,按300条/cm²土壤的量施用线虫,对照杨桃园的桔小实蝇种群趋势指数为105.9,而处理杨桃园的桔小实蝇种群趋势指数下降为15.5;小卷蛾斯氏线虫All品系对桔小实蝇的干扰控制指数为0.146,即线虫处理果园的下代种群密度仅为对照果园的14.6%。     

Screening of entomopathogenic nematodes for virulence against the invasive western corn rootworm, Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae) in Europe

Entomopathogenic nematode species available in Europe were screened for their efficacy against both the root-feeding larvae and silk-feeding adults of the western corn rootworm, Diabrotica virgifera virgifera LeConte. Laboratory screening tests were aimed at the selection of candidate biological control agents for the management of this invasive alien pest in Europe. Steinernema glaseri, S. arenarium, S. abassi, S. bicornutum, S. feltiae, S. kraussei, S. carpocapsae and Heterorhabditis bacteriophora were studied to determine their virulence against third instar larvae and adults of D. v. virgifera in small-volume arenas (using nematode concentrations of 0.5, 0.8, 7.9 and 15.9 infective juveniles cm-2). All nematode species were able to invade and propagate in D. v. virgifera larvae, but adults were rarely infected. At concentrations of 7.9 and 15.9 cm-2, S. glaseri, S. arenarium, S. abassi and H. bacteriophora caused the highest larval mortality of up to 77%. Steinernema bicornutum, S. abassi, S. carpocapsae and H. bacteriophora appeared to have a high propagation level, producing 5970+/-779, 5595+/-811, 5341+/-1177 and 4039+/-1025 infective juveniles per larva, respectively. Steinernema glaseri, S. arenarium, S. feltiae, S. kraussei and H. bacteriophora were further screened at a concentration of 16.7 nematodes cm-2 against third instar larvae in medium-volume arenas (sand-filled trays with maize plants). Heterorhabditis bacteriophora, S. arenarium and S. feltiae caused the highest larval mortality with 77+/-16.6%, 67+/-3.5%, and 57+/-17.1%, respectively. In a next step, criteria for rating the entomopathogenic nematode species were applied based on results obtained for virulence and propagation, and for current production costs and availability in Europe. These criteria were then rated to determine the potential of the nematodes for further field testing. Results showed the highest potential in H. bacteriophora, followed by S. arenarium and S. feltiae, for further testing as candidate biological control agents.     

Susceptibility of the filbertworm (Cydia latiferreana, Lepidoptera: Tortricidae) and filbert weevil (Curculio occidentalis, Coleoptera: Curculionidae) to entomopathogenic nematodes

The objective of this study was to determine the susceptibility of the two primary direct insect pests of hazelnuts in Oregon to three species of entomopathogenic nematodes. The entomopathogenic nematodes (Heterorhabditis marelatus Pt. Reyes, Steinernema carpocapsae All and Steinernema kraussei L137) were used in laboratory soil bioassays to determine their virulence against filbertworm, Cydia latiferreana (Walsingham) (Lepidoptera: Tortricidae) and filbert weevil, Curculio occidentalis (Casey) (Coleoptera: Curculionidae). All three nematode species were infective in laboratory bioassays. Infectivity ranged from 73-100% and 23-85% for filbertworm and filbert weevil, respectively. Field results were similar to those found in the laboratory with filbertworm larvae being more susceptible to nematode infection.     

Entomopathogenic Nematodes for Control of Codling Moth,Cydia pomonella(Lepidoptera: Tortricidae): Effect of Nematode Species, Concentration, Temperature, and Humidity

The susceptibility of codling moth diapausing larvae to three entomopathogenic nematode species was assessed in the laboratory using a bioassay system that employed cocooned larvae within cardboard strips. The LC₅₀values forSteinernema carpocapsae, S. riobrave,andHeterorhabditis bacteriophorawere 4.7, 4.8, and 6.0 infective juveniles/cm², respectively. When a discriminating concentration of 10 infective juveniles/cm²of each of the three nematode species was evaluated at 15, 20, 25, and 30°C,S. carpocapsaewas the most effective nematode with mortalities ranging from 66 to 90%. Mortalities produced byS. riobraveandH. bacteriophoraat the four temperatures were 2–94 and 25–69%, respectively. Studies were also conducted to test infectivity at 10, 35, and 40°C. No mortality was produced by any of the nematode species at 10°C.S. riobravewas the most infective nematode at 35°C producing 68% mortality which was more than twice that observed forS. carpocapsaeorH. bacteriophora.Codling moth larvae treated with 10 infective juveniles/cm²ofS. carpocapsaeand kept in 95+% RH at 25°C for 0–24 h followed by incubation at 25–35% RH indicated that more than 3 h in high humidity was needed to attain 50% mortality. Trials ofS. carpocapsae, S. riobrave,andH. bacteriophoraat 50 infective juveniles/cm²against cocooned larvae on pear and apple logs resulted in reductions of codling moth adult emergence of 83, 31, and 43%, respectively, relative to control emergence. Trials of the three entomopathogenic nematodes at 50 infective juveniles/cm²against cocooned larvae in leaf litter resulted in 99 (S. carpocapsae), 80 (S. riobrave), and 83% (H. bacteriophora) mortality, respectively. Our results indicate good potential of entomopathogenic nematodes, especiallyS. carpocapsae,for codling moth control under a variety of environmental conditions.     

Susceptibility of the peachtree borer, Synanthedon exitiosa, to Steinernema carpocapsae and Steinernema riobrave in laboratory and field trials

The nematode Steinernema carpocapsae (All) strain was significantly more effective against peachtree borer larvae (Synanthedon exitiosa [Lepidoptera: Sesiidae]) than Steinernema riobrave (7-12) strain in field and laboratory experiments. Eighty-eight percent control of peachtree borer larvae was obtained with S. carpocapsae in the field trial when applied at 3 x 10(5) infective juveniles per tree, and 92% mortality was obtained in the lab assay using 50 infective juveniles per larva.     

Multiple-species natural enemy approach for biological control of alfalfa snout beetle (Coleoptera: Curculionidae) using entomopathogenic nematodes

Multiple-species natural enemy approach for the biological control of the alfalfa snout beetle, Otiorhynchus ligustici (L.) (Coleoptera: Curculionidae), was compared with using single-species of natural enemies in the alfalfa ecosystem by using entomopathogenic nematodes with different dispersal and foraging behaviors. Steinernema carpocapsae NY001 (ambush nematode), Heterorhabditis bacteriophora Oswego (cruiser nematode), and Steinernema feltiae Valko (intermediate nematode) were applied in single-species, two-species combinations, and one three-species combination treatments at 2.5 x 10(9) infective juveniles per hectare. All nematode species persisted for a full year (357 d). S. carpocapsae NY001 protected the plants from root-feeding damage better than H. bacteriophora Oswego but allowed for higher larval survival than all other nematode treatments. S. feltiae Valko protected the plants better than H. bacteriophora Oswego and controlled alfalfa snout beetle larvae better than S. carpocapsae NY001. H. bacteriophora Oswego allowed for similar root damage compared with control plots but reduced larval populations better than S. carpocapsae NY001. The combination of S. carpocapsae NY001 and H. bacteriophora Oswego provided significantly better protection for the plants than the control (unlike H. bacteriophora Oswego alone) and reduced host larva survival more than S. carpocapsae NY001 alone. The combination S. feltiae Valko and H. bacteriophora Oswego could not be statistically separated from the performance of S. feltiae Valko applied alone.     

Interactions of two idiobiont parasitoids (Hymenoptera: Ichneumonidae) of codling moth (Lepidoptera: Tortricidae) with the entomopathogenic nematode Steinernema carpocapsae (Rhabditida: Steinernematidae)

Simultaneous use of parasitoids and entomopathogenic nematodes for codling moth (CM) control could produce an antagonistic interaction between the two groups resulting in death of the parasitoid larvae. Two ectoparasitic ichneumonid species, Mastrus ridibundus and Liotryphon caudatus, imported for classical biological control of cocooned CM larvae were studied regarding their interactions with Steinernema carpocapsae. Exposure of M. ridibundus and L. caudatus developing larvae to infective juveniles (IJs) of S. carpocapsae (10 IJs/cm2; approximately LC(80-90) for CM larvae) within CM cocoons resulted in 70.7 and 85.2% mortality, respectively. However, diapausing full grown parasitoid larvae were almost completely protected from nematode penetration within their own tightly woven cocoons. M. ridibundus and L. caudatus females were able to detect and avoid ovipositing on nematode-infected cocooned CM moth larvae as early as 12h after treatment of the host with IJs. When given the choice between cardboard substrates containing untreated cocooned CM larvae and those treated with an approximate LC95 of S. carpocapsae IJs (25 IJs/cm2) 12, 24, or 48h earlier, ovipositing parasitoids demonstrated a significant preference for untreated larvae. The ability of these parasitoids to avoid nematode-treated larvae and to seek out and kill cocooned CM larvae that survive nematode treatments enhances the complementarity of entomopathogenic nematodes and M. ridibundus and L. caudatus.     

Steinernema carpocapsae (Rhabditida: Steinernematidae) as a biological control agent against the fungus Gnat Bradysia agrestis (Diptera: Sciaridae) in propagation houses

A recently introduced fungus gnat, Bradysia agrestis, has caused serious problems in Korean propagation houses where vegetable seedlings are produced for transplant into the fields. Although chemical insecticides are available against this pest, alternate control measures are needed. A Korean isolate of the entomopathogenic nematode, Steinernema carpocapsae Pocheon strain, was tested against this insect in the laboratory and propagation house. In the laboratory, S. carpocapsae affected oviposition, with the untreated females laying an average of 121±25 eggs, whereas the treated females averaged 7±2 eggs. The infectivity of S. carpocapsae to the fungus gnat was affected by the developmental stage and temperature, with highest mortality observed with the third and fourth instars and pupal stage. Nematode mortality in the second instar fungus gnat ranged between 23 and 35%, but showed no significant differences among the temperatures tested. The egg and first instar were not infected by the nematode. In nematode dispersal studies, adult female fungus gnats alone dispersed S. carpocapsae from the nematode-treated area to the control area at a higher rate than male and female gnats or male gnats alone. In the propagation house experiments with watermelon seedlings, no significant difference was observed in fungus gnat larval reduction at S. carpocapsae concentrations of 5, 10, or 20 infective juveniles (IJs)/g of soil at 7, 14, and 21 days after treatment. In comparison with the control, the S. carpocapsae treatments significantly reduced B. agrestis larval numbers. When the watermelon seed was treated with S. carpocapsae at sowing, the larval density of B. agrestis was significantly reduced, that is, the number of B. agrestis larvae ranged from four to eight and from five to eight in the nematode-treated plots compared with 26 and 30 in the control plots on the 17th and 34th day post-treatment, respectively. In the chemical insecticide treatments, diflubenzuron and chlorpyrifos were significantly more effective than S. carpocapsae and diazinon in reducing larval populations of the fungus gnat. Our data show that, although some of the chemical insecticides were more effective than S. carpocapsae Pocheon strain, the nematode was still an effective tool for management of the fungus gnat larvae and in protecting seedlings from damage in propagation houses.     

Haemocytes immunity of rose sawfly,Arge ochropus (Hym.: Argidae) against entomopathogenic nematodes,Steinernema carpocapsae and Heterorhabditis bacteriophora

The rose sawfly, Arge ochropus (Gmelin), is one of the most destructive pests attacking rose bushes in northern Iran. In the present study, the haemocyte reactions of A. ochropus larvae were assessed against two entomopathogenic nematodes, Steinernema carpocapsae (Weiser) and Heterorhabditis bacteriophora Poinar. With injection of infective juveniles of H. bactriophora into A. ochropus larvae, the total haemocyte count showed alternating fluctuations at all time intervals. Encapsulation occurred 22 hours post injection (hpi) of H. bacteriophora infective juveniles into the rose sawfly larvae, while melanization was observed after 24 h. In the case of S. carpocapsae, initial attachment of the haemocytes was detected at 18 hpi and complete encapsulation at 24 hpi; no melanization was observed. In general, findings showed strong immune responses of the rose sawfly larvae against H. bacteriophora, while these reactions were weakened for S. carpocapsae. Therefore, it is concluded that S. carpocapsae has more ability to overcome the host defence system, and this research provides a new window on its potential as a biocontrol agent.     

Field Efficacy of Entomopathogenic Nematodes against the Sugar-beet Weevil Temnorhinus ( = Conorrhynchus ) mendicus Gyll. (Coleoptera: Curculionidae)

In 1992 and 1993, the field effectiveness of Heterorhabditis sp. (NL-HL81 strain), H. bacteriophora (HP 88 strain) and Steinernema carpocapsae ('All' strain) against the larvae of Temnorhinus mendicus Gyll. was assessed. The biological tests were compared with two chemical treatments (cypermethrin or deltamethrin) and one untreated control. In 1992, S. carpocapsae gave better results than Heterorhabditis sp. in reducing the percentage of infested roots, as compared with the untreated sample and the chemical one; similarly, the irrigated control gave the best results. In 1993, three concentrations of entomopathogenic nematodes (EPNs) were tested: 0.250 106 infective juveniles (IJs) m - 2, 0.125 106 IJs m - 2 and 0.075 106 IJs m - 2. The different numbers of EPNs did not give very different results from each other; however, H. bacteriophora at 0.075 106 IJs m - 2 was the least effective. In general, cypermethrin was more effective than deltamethrin, but one treatment with EPNs followed by irrigation was always more effective than two chemical applications.     

Susceptibility of Pseudaletia unipuncta (Lepidoptera: Noctuidae) to entomopathogenic nematodes (Rhabditida: Steinernematidae and Heterorhabditidae) isolated in the Azores: effect of nematode strain and host age

The armyworm, Pseudaletia unipuncta (Haworth), is a serious pest to the Azores's pastures. In laboratory bioassays we tested the susceptibility of this insect to entomopathogenic nematodes isolated in Azores: Steinernema carpocapsae Az20, Az150, and A48 strains, S. glaseri Az26 strain and Heterorhabditis bacteriophora Az33 strain. The A48, Az20, and Az150 strains caused parasitism rates of 96.6, 90, and 53.3%, and mortality rates of 63.3, 46.6, and 23.3%, respectively, to sixth instar. The Az33 strain caused a parasitism rate of 73.3% and a mortality rate of 40%; whereas, the Az26 strain caused a parasitism rate of 40% and no mortality. A linear response dose-parasitism with a positive regression (r2 = 0.993) was observed in insects exposed to S. carpocapsae Az150 strain. Positive regressions were also observed between mortality and dose rate for S. carpocapsae A48 (r2 = 0.980), Az20 (r2 = 0.956), and Az150 (r2 = 0.963) strains, and H. bacteriophora Az33 strain (r2 = 0.999). Fourth instars were the most susceptible to the A48 strain, followed by the fifth instars, while the sixth instars were the less susceptible, with LD50 values of 26.2, 62.8, and 320.7 infective juveniles, respectively. The lethal time for each of the tested instars was 32.3, 35.5, and 49.2 h, respectively. The invasion rate was 33.5, 28.2, and 40.8 nematodes per treated larvae in the fourth, fifth, and sixth instars, respectively.     

Susceptibility and behavioral response of red imported fire ant (Hymenoptera: Formicidae) to selected entomogenous nematodes (Rhabditida: Steinernematidae & Heterorhabditidae).

Pathogenicity of infective juveniles of selected Steinernema spp. and Heterorhabditis spp. toward developing and reproductive stages of the red imported fire ant, Solenopsis invicta Buren, was tested under laboratory conditions. At 10(3)-10(5) infective juveniles per Petri dish, mortality of reproductive larvae, pupae, and alates ranged from 28 to 100% at higher doses after 96 h at 23-25 degrees C. Steinernema carpocapsae All was the most consistent species tested; this nematode caused mortality of fire ant larvae, pupae, and alates of 82-94, 64-96, and 38-99%, respectively. Although not susceptible to nematode infection, worker ants vigorously preened nematodes from brood, alates, and themselves. In a field study, S. carpocapsae (5 x 10(6) and 2 x 10(6) drench, 2 x 10(6) infective juvenile infection) was applied to active fire ant mounds in 3.8-liter suspensions. Hydramethylnon (75 ml), a water drench, a water injection, and untreated fire ant mounds were marked and treated. Overall activity in mounds treated with nematodes of hydramethylnon ranged from 40 to 48%. Satellite mound activity accounted for 32-44% of overall activity in mounds treated with nematodes 2 wk after treatment. However, 6 wk after treatment, activity in mounds treated with hydramethylnon was 44%; activity of mounds treated with nematodes ranged from 52 to 80%. Satellite mound activity accounted for 0-24% of overall activity. Whereas a soil drench of S. carpocapsae showed potential as a control method for the red imported fire ant, colony relocation after nematode treatment could limit overall efficacy unless application techniques are developed to overcome or take advantage of the movement.     

Efficacy of entomopathogenic nematodes against soil-dwelling life stages of western flower thrips, Frankliniella occidentalis (Thysanoptera: Thripidae).

The efficacy of six entomopathogenic nematode (EPN) strains was tested in a laboratory study against soil-dwelling life stages of western flower thrips (WFT), Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae). The EPN strain collections screened included two Heterorhabditis bacteriophora species, i.e., H. bacteriophora HK3 (H.b H) and H. bacteriophora HB Brecan (H.b B), three Steinernema feltiae species, i.e., S. feltiae Sylt (S.f S), S. feltiae OBSIII (S.f O), and S. feltiae strain CR (S.f C), and the S. carpocapsae strain DD136 (S.c D). All soil-dwelling life stages of WFT were susceptible to the tested EPN strains. The most virulent strains were S.f S, S.c D, and H.b H. The S.f O strain was highly virulent against late second instar larvae and prepupae of WFT under high soil moisture conditions, but less effective against pupae under comparatively drier soil conditions. Results from dose rate experiments indicate that a comparatively high concentration of 400 infective juveniles (IJs) per cm(2) was needed to obtain high mortality in all soil-dwelling life stages of WFT. However, dose rates of 100-200 IJs/cm(2) already caused 30-50% mortality in WFT. The chances for combining EPNs with other biological control agents of WFT are discussed.     

Distribution of entomopathogenic nematodes (Steinernematidae and Heterorhabditidae) in natural habitats in California, USA

A total of 270 soil samples from 30 different habitats in 10 geographic regions of California were evaluated for the presence of rhabditid entomopathogenic nematodes. Nematodes were isolated from 26.3% of the samples. The recovered isolates were identified as Steinernema carpocapsae, S. feltiae, S. kraussei, S. longicaudum, S. oregonense, Heterorhabditis marelatus and H.bacteriophora. Among the steinernematids, S. kraussei and S. feltiae were the most commonly encountered species, generally occurring in acidic soils high in organic matter. Among the heterorhabditids, H. bacteriophora was isolated along the southern coast, whereas H. marelatus was recovered along the northern coast of California. Steinernematids were recovered from coniferous forests, oak woodlands and grasslands whereas heterorhabditids were isolated from coastal marshes.     

Effectiveness of Entomopathogenic Nematodes in an Alginate Gel Formulation Against Lepidopterous Pests

An improved calcium alginate gel formulation was developed and tested as a carrier for entomopathogenic nematodes against Spodoptera littoralis and Helicoverpa armigera larvae. Mortality of 100% was caused in 4th instar larvae of the two insects by feeding them on 1000 infective juveniles (IJ) g -1 of Steinernema carpocapsae (ALL strain) in the gel for 24 h. Exposing 2nd to 5th instars of H. armigera and 3rd to 6th of S. littoralis to 500 IJ g -1 of S. carpocapsae (ALL strain) resulted in 70-100% larval mortality. Mature larvae were less susceptible to the nematodes. Mortality of larvae exposed to 500 IJg -1 of S. carpocapsae (ALL strain) ranged from about 45-55% at 4 h to 90-95% at 48 h. Fourth instar larvae fed for 24 h with 250 IJ g -1 of nematode strains in gel showed in S. littoralis ranges of susceptibility in the following descending order: S. feltiae (IS -7 strain) = S. carpocapsae (DT strain) = S. feltiae (IS-6 strain) > S. carpocapsae (Mexican strain) = S. carpocapsae (ALL strain) = Heterorhabditis bacteriophora (HP-88 strain) = H sp. (IS-5 strain) > S. riobravae (Texas strain); in H. armigera the rating was: S. feltiae (IS-7 strain) = H. bacteriophora (HP88 strain) > S. carpocapsae (ALL strain) = S. feltiae (IS-6 strain ) = Heterorhabditis sp. (IS5 strain) > S. carpocapsae (Mexican strain) > S. riobravae (Texas strain) . The number of nematodes per larval cadaver increased with mortality rates. In greenhouse tests at 28 &#45 2°C and 90% relative humidity, gel discs containing 500 IJ g -1 of nematodes were pinned to leaves of potted plants of cotton ( Gossypium hirsutum ) (Acala SJ2) and the plants were offered to S. littoralis larvae. Larval mortality of 89 &#45 12.7% was caused by S. feltiae (IS-7 strain) and most of the plant leaves were protected against the larvae by the nematodes. In the control, larval mortality was 3.3 &#45 0.05% and the plants were almost completely defoliated. Possibilities of using the gel-nematode formulation to protect sheltered crops against insect pests are discussed     

Susceptibility of the strawberry crown moth (Lepidoptera: Sesiidae) to entomopathogenic nematodes

The objective of this study was to determine the susceptibility of the strawberry crown moth, Synanthedon bibionipennis (Boisduval) (Lepidoptera: Sesiidae) larvae to two species of entomopathogenic nematodes. The entomopathogenic nematodes Steinernema carpocapsae (Weiser) strain Agriotos and Heterorhabditis bacteriophora (Steiner) strain Oswego were evaluated in laboratory soil bioassays and the field. Both nematode species were highly infective in the laboratory bioassays. Last instars were extremely susceptible to nematode infection in the laboratory, even in the protected environment inside the strawberry (Fragaria x ananassa Duch.) crown. Infectivity in the laboratory was 96 and 94% for S. carpocapsae and H. bacteriophora, respectively. Field applications in late fall (October) were less effective with S. carpocapsae and H. bacteriophora, resulting in 51 and 33% infection, respectively. Larval mortality in the field from both nematode treatments was significantly greater than the control, but treatments were substantially less efficacious than in the laboratory. Soil temperature after nematode applications in the field (11 degrees C mean daily temperature) was below minimum establishment temperatures for both nematode species for a majority of the post-application period. It is clear from laboratory data that strawberry crown moth larvae are extremely susceptible to nematode infection. Improved control in the field is likely if nematode applications are made in late summer to early fall when larvae are present in the soil and soil temperatures are more favorable for nematode infection.     

Influence of soil temperature and moisture on the infectivity of entomopathogenic nematodes (Rhabditida: Heterorhabditidae, Steinernematidae) against larvae of Ceratitis capitata (Wiedemann) (Diptera: Tephritidae)

The Mediterranean fruit fly, Ceratitis capitata (Wiedemann), is considered one of the main pests that affect fruit production in the world. This insect spends part of its life cycle in the soil, making it a target for entomopathogenic nematodes. This work aimed at evaluating the influence of soil temperature and moisture on the infectivity of Heterorhabditis sp. RSC01 and Steinernema carpocapsae ALL to third-instars of C. capitata, and to compare the efficiency of these isolates at five different soil temperatures (19, 22, 25, 28, and 31°C) and three levels of relative soil moisture (100, 75, and 50% of field capacity). Ten C. capitata larvae were transferred to plastic jars (12 cm × 6 cm) containing 100 g soil, followed by the application of an aqueous suspension containing 125 infective juveniles (IJ)/cm2. In the control treatment, 3 ml of distilled water was applied. Mortality evaluations were made five days later and were confirmed by observations of the characteristic symptoms and cadaver dissection. The infectivity was directly proportional to temperature increase, with maximum percent mortality of 86.7% and 80.0% for S. carpocapsae and Heterorhabditis sp., respectively, at 31°C. At 25°C, the highest mortality for both species was obtained at 75% of field capacity (96.7% and 26.7% for S. carpocapsae and Heterorhabditis sp., respectively).     

Parasitism of bark scorpion Centruroides exilicauda (Scorpiones: Buthidae) by entomopathogenic nematodes (Rhabditida: Steinernematidae; Heterorhabditidae)

In laboratory bioassays, Steinernema glaseri Steiner, Steinernema riobrave Cabanillas, Poinar & Raulston, Heterorhabditis bacteriophora Poinar, and Heterorhabditis marelatus Liu & Berry were capable of infecting and killing the bark scorpion, Centruroides exilicauda (Wood). Steinernema feltiae (Filipjev) and Steinernema carpocapsae (Weiser) failed to infect C. exilicauda at 22 degrees C. S. glaseri, H. marelatus, and H. bacteriophora caused significant mortality at 22 degrees C, indicating the potential role of these parasites as a biocontrol option. Efficacy of S. glaseri and H. bacteriophora was reduced in an assay conducted at 25 degrees C. Only S. glaseri was able to reproduce in the target host. Dissection of scorpions at the end of the experimental periods revealed inactive juvenile S. riobrave, H. marelatus, and H. bacteriophora nematodes. Both mermithid and oxyurid nematodes have been documented as nematode parasites of scorpions, but rhabditids have not been reported until now. Field studies are warranted to assess the usefulness of entomopathogenic nematodes as biocontrol agents of bark scorpions.     

Virulence of entomopathogenic nematodes (Rhabditida: Steinernematidae, Heterorhabditidae) against Tipula paludosa (Diptera: Tipulidae), a turfgrass pest on golf courses

The European crane fly (ECF), Tipula paludosa Meigen feeds on leaves, crowns, and roots of cool-season turfgrasses causing damage to residential lawns and golf courses. A laboratory study was conducted to determine the susceptibility of ECF larvae to four commercial entomopathogenic nematode (EPN) species (Heterorhabditis marelatus, H. megidis, Steinernema carpocapsae and S. feltiae). The virulence of four S. feltiae isolates recovered from golf courses in Quebec and Ontario were also compared to a commercial strain. LC₅₀ values of EPN against late instar ECF larvae were 152, 562, 763, and 3584 for S. feltiae, H. megidis, H. marelatus and S. carpocapsae, respectively. When non-feeding (without grass seedling), ECF larvae mortalities decreased for all nematode species and concentrations tested. At 25°C, LC₅₀ values for the two most virulent indigenous S. feltiae were 129 and 187 nematodes/larva, not different from the commercial strain. At 5°C, the commercial S. feltiae was more effective than both BIC14A and RE6A isolates against ECF larvae. However, at 15°C, BIC14A was the most virulent at the low concentration of 200 IJs/larva.