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.     

Susceptibility of diamond back moth,Plutella xylostella (L) to entomopathogenic nematodes

Eight entomopathogenic nematode species / strains, Steinernema glaseri (steiner), S. carpocapsae (Weiser), S. feltiae (Filipjev), Steinernema sp. Ecomax strain, Heterorhabditis bacteriophora (Pioner), Heterorhabditis sp. Ecomax strain, two locally isolated strains called as JFC and TFC were tested against the final instar larvae of diamond back moth, Plutella xylostella (L.). All nematodes were found pathogenic. However, H. bacteriophora was adjudged the most pathogenic amongst the test nematodes on the basis of LD50 (9.16 IJS/larva), LT50 (43.26 hr), Lex T50 (3.24 hr) and the propagation potential (average of 271.42 IJS/mg) on the host body weight.     

Directional movement of entomopathogenic nematodes in response to electrical field: effects of species, magnitude of voltage, and infective juvenile age

Entomopathogenic nematodes respond to a variety of stimuli when foraging. Previously, we reported a directional response to electrical fields for two entomopathogenic nematode species; specifically, when electrical fields were generated on agar plates Steinernema glaseri (a nematode that utilizes a cruiser-type foraging strategy) moved to a higher electric potential, whereas Steinernema carpocapsae, an ambush-type forager, moved to a lower potential. Thus, we hypothesized that entomopathogenic nematode directional response to electrical fields varies among species, and may be related to foraging strategy. In this study, we tested the hypothesis by comparing directional response among seven additional nematode species: Heterorhabditis bacteriophora, Heterorhabditis georgiana, Heterorhabditis indica, Heterorhabditis megidis, Steinernema feltiae, Steinernema riobrave, and Steinernema siamkayai. S. carpocapsae and S. glaseri were also included as positive controls. Heterorhabditids tend toward cruiser foraging approaches whereas S. siamkayai is an ambusher and S. feltiae and S. riobrave are intermediate. Additionally, we determined the lowest voltage that would elicit a directional response (tested in S. feltiae and S. carpocapsae), and we investigated the impact of nematode age on response to electrical field in S. carpocapsae. In the experiment measuring diversity of response among species, we did not detect any response to electrical fields among the heterorhabditids except for H. georgiana, which moved to a higher electrical potential; S. glaseri and S. riobrave also moved to a higher potential, whereas S. carpocapsae, S. feltiae, and S. siamkayai moved to a lower potential. Overall our hypothesis that foraging strategy can predict directional response was supported (in the nematodes that exhibited a response). The lowest electric potential that elicited a response was 0.1 V, which is comparable to electrical potential associated with some insects and plant roots. The level of response to electrical potential diminished with nematode age. These results expand our knowledge of electrical fields as cues that may be used by entomopathogenic nematodes for host-finding or other aspects of navigation in the soil.     

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.     

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.     

Host cadavers protect entomopathogenic nematodes during freezing

The entomopathogenic nematodes Heterorhabditis bacteriophora, Steinernema carpocapsae, Steinernema glaseri, and Steinernema feltiae were exposed to freezing while inside their hosts. Survival was assessed by observing live and dead nematodes inside cadavers and by counting the infective juveniles (IJs) that emerged after freezing. We (1) measured the effects of 24h of freezing at different times throughout the course of an infection, (2) determined the duration of freezing entomopathogenic nematodes could survive, (3) determined species differences in freezing survival. Highest stage-specific survival was IJs for S. carpocapsae, and adults for H. bacteriophora. When cadavers were frozen two or three days after infection, few IJs emerged from them. Freezing between five and seven days after infection had no negative effect on IJ production. No decrease in IJ production was measured for H. bacteriophora after freezing. H. bacteriophora also showed improved survival inside versus outside their host when exposed to freezing.     

Virulence of entomopathogenic nematodes to pecan weevil larvae, Curculio caryae (Coleoptera: Curculionidae), in the laboratory

The pecan weevil, Curculio caryae (Horn), is a key pest of pecans in the Southeast. Entomopathogenic nematodes have been shown to be pathogenic toward the larval stage of this pest. Before this research, only three species of nematodes had been tested against pecan weevil larvae. In this study, the virulence of the following nine species and 15 strains of nematodes toward fourth-instar pecan weevil was tested: Heterorhabditis bacteriophora Poinar (Baine, HP88, Oswego, NJ1, and Tf strains), H. indica Poinar, Karunakar & David (original and Homl strains), H. marelatus Liu & Berry (IN and Point Reyes strains), H. megidis Poinar, Jackson & Klein (UK211 strain), H. zealandica Poinar (NZH3 strain), Steinernema riobrave Cabanillas, Poinar & Raulston (355 strain), S. carpocapsae (Weiser) (All strain), S. feltiae (Filipjev) (SN strain), and S. glaseri (Steiner) (NJ43 strain). No significant difference in virulence was detected among nematode species or strains. Nematode-induced mortality was not significantly greater than control mortality (in any of the experiments conducted) for the following nematodes: H. bacteriophora (Baine), H. zealandica (NZH3), S. carpocapsae (All), S. feltiae (SN), S. glaseri (NJ43), and S. riobrave (355). All other nematodes caused greater mortality than the control in at least one experiment. Heterorhabditis megidis (UK211) but not H. indica (original) displayed a positive linear relationship between nematode concentration and larval mortality. Results suggested that, as pecan weevil larvae age, they may have become more resistant to infection with entomopathogenic nematodes.     

Effectiveness of different species of entomopathogenic nematodes for biocontrol of the Mediterranean flatheaded rootborer, Capnodis tenebrionis (Linné) (Coleoptera: Buprestidae) in potted peach tree

The susceptibility of larvae of the Mediterranean flatheaded rootborer (Capnodis tenebrionis) to 13 isolates of entomopathogenic nematodes was examined using GF-677 potted trees (peachxalmond hybrid) as the host plant. The nematode strains tested included nine Steinernema feltiae, one S. affine, one S. carpocapsae and two Heterorhabditis bacteriophora. Nematodes showed the ability to locate and kill larvae of C. tenebrionis just after they enter into the roots of the tree. S. feltiae strains provided an efficacy ranging from 79.68% to 88.24%. H. bacteriophora strains resulted in control of 71.66-76.47%. S. carpocapsae (B14) and S. affine (Gspe3) caused lower control of C. tenebrionis larvae (62.03% and 34.76%, respectively). The influence of foraging strategy and the use of autochthonous nematodes to control C. tenebrionis larvae inside the roots is discussed.     

Entomopathogenic Nematode Infectivity Assay: Comparison of Penetration Rate into Different Hosts

Penetration rate (the percentage of the initial infective juvenile inoculum that invades an insect host) was tested as an indicator of entomopathogenic nematode infectivity. Several host-parasite-substrate combinations were evaluated for penetration rate. Four steinernematids, Steinernema carpocapsae, S. glaseri, S. feltiae, S. riobravis and two strains of Heterorhabditis bacteriophora were tested in a contact bioassay against the wax moth, Galleria mellonella, the yellow meal worm, Tenebrio molitor, the beet armyworm, Spodoptera exigua, the black cutworm, Agrotis ipsilon, and the European corn borer, Ostrinia nubilalis. The insect larvae were confined individually in sand and filter paper arenas and exposed to 200 infective juveniles. After incubation, dead insects were dissected in order to count the nematodes penetrated. The data were analyzed for the effects of nematode strain and substrate on penetration rate. The bioassay substrate had a variable effect depending on the insect species. The nematode effect was highly significant for all insects tested. The penetration rate therefore allowed comparisons among nematode strains invading a host. Nematode ranking for infectivity differed according to the insect tested.     

Distribution patterns of entomopathogenic nematodes applied through drip irrigation systems

The distribution of entomopathogenic nematodes applied by drip irrigation was evaluated by injecting small volumes of Steinernema carpocapsae (Weiser) All strain, Steinernema feltiae (Filipjev) SN strain, Steinernema glaseri Steiner, and Heterorhabditis bacteriophora HP 88 strain Poinar suspensions into drip irrigation lines. Additionally, Steinernema riobrave Cabanillas, Poinar, & Raulston, and S. carpocapsae were injected in a 10-liter volume of water with an injection pump. Overall, the nematodes were evenly distributed along the drip lines. The total number of nematodes recovered from drip emitters was variable ranging from 42 to 92%. However, drip irrigation lines have potential to deliver entomopathogenic nematodes efficiently into pest habitats.     

Spatial and temporal distribution of endemic and released entomopathogenic nematode populations in turfgrass

Entomopathogenic nematodes (Rhabdita: Heterorhabditidae and Steinernematidae) have been effective as inundative biological control agents of scarab larvae (Coleoptera: Scarabaeidae) in turfgrass. Entomopathogenic nematodes also occur naturally in turfgrass and endemic or inoculated populations may be able to provide effective long-term control. Variation in Heterorhabditis bacteriophora and Steinernema carpocapsae spatial and temporal distribution along transects placed at different turfgrass sites in central New Jersey, USA, was investigated. H. bacteriophora tended to be recovered from fewer sections in a transect than S. carpocapsae, but the two species, overall, did not differ in patchiness of distribution. In one transect with a H. bacteriophora population S. feltiae was also recovered, but the two populations seldom overlapped spatially. In transects with adequate scarab larvae density for analysis, H. bacteriophora density and Popillia japonica larvae density were inversely correlated. This suggests that endemic H. bacteriophora populations may suppress P. japonica populations. In one transect, an epizootic of H. bacteriophora in an undetermined host may have occurred. Edaphic factors were relatively uniform along transects and were, at most, weakly correlated with nematode recovery. Uniform inoculative releases of H. bacteriophora tended to return to patterns of distribution typical of endemic populations.     

Controlling the sugar beet fly Pegomyia mixta Vill. with entomopathogenic nematodes

Sugar beet, Beta vulgaris L. is a strategic crop of sugar industry in Egypt. It is threatened by several insect pests among most important of them is the beet fly Pegomyia mixta. This work deals with the biological control of this insect using four entomopathogenic nematodes (EPNs). The nematodes included Steinernema carpocapsae S2, Steinernema feltiae, Heterorhabditis bacteriophora (HB1-3) and Heterorhabditis bacteriophora S1. Daily mortality of larvae and pupae of P. mixta were recorded after treatment with serial concentrations (500, 1000, 2000 and 4000 infective juveniles (IJs)/ml) of each of four studied EPNs. In the laboratory all tested nematodes killed the larvae inside their mines in the sugar beet leaves and developed in their bodies in different extends. They also killed the insect pupae in the soil and developed in their bodies. Young larvae were more susceptible than old ones. New pupae were more susceptible than old ones. In the field a single spray of S. feltiae or H. bacteriophora caused 81.3 or 75.9% reduction in the larval population of the in sugar beet leaves.     

Relationship between the successful infection by entomopathogenic nematodes and the host immune response

Reproduction of entomopathogenic nematodes requires that they escape recognition by a host's immune system or that they have mechanisms to escape encapsulation and melanization. We investigated the immune responses of larvae for the greater wax moth (Galleria mellonella), tobacco hornworm (Manduca sexta), Japanese beetle (Popillia japonica), northern masked chafer (Cyclocephala borealis), oriental beetle (Exomala orientalis) and adult house crickets (Acheta domesticus), challenged with infective juveniles from different species and strains of entomopathogenic nematodes. The in vivo immune responses of hosts were correlated with nematode specificity and survival found by infection assays. In P. japonica, 45% of injected infective juveniles from Steinernema glaseri NC strain survived; whereas the hemocytes from the beetle strongly encapsulated and melanized the Heterorhabditis bacteriophora HP88 strain, S. glaseri FL strain, Steinernema scarabaei and Steinernema feltiae. Overall, H. bacteriophora was intensively melanized in resistant insect species (E. orientalis, P. japonica and C. borealis) and had the least ability to escape the host immune response. Steinernema glaseri NC strain suppressed the immune responses in susceptible hosts (M. sexta, E. orientalis and P. japonica), whereas S. glaseri FL strain was less successful. Using an in vitro assay, we found that hemocytes from G. mellonella, P. japonica, M. sexta and A. domestica recognized both nematode species quickly. However, many S. glaseri in M. sexta and H. bacteriophora in G. mellonella escaped from hemocyte encapsulation by 24h. These data indicate that, while host recognition underlies some of the differences between resistant and susceptible host species, escape from encapsulation following recognition can also allow successful infection. Co-injected surface-coat proteins from S. glaseri did not protect H. bacteriophora in M. sexta but did protect H. bacteriophora in E. orientalis larva; therefore, surface coat proteins do not universally convey host susceptibility. Comparisons of surface coat proteins by native and SDS-PAGE demonstrated different protein compositions between H. bacteriophora and S. glaseri and between the two strains of S. glaseri.     

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     

Laboratory Evaluation of Seven Pakistani Strains of Entomopathogenic Nematodes Against a Stored Grain Insect Pest, Pulse beetle Callosobruchus chinensis (L.)

Seven Pakistani strains of entomopathogenic nematodes belonging to the genera Steinernema and Heterorhabditis were tested against last instar and adult stages of the pulse beetle, Callosobruchus chinensis (L.). These nematodes included Steinernema pakistanense Shahina, Anis, Reid and Maqbool (Ham 10 strain); S. asiaticum Anis, Shahina, Reid and Rowe (211 strain); S. abbasi Elawad, Ahmad and Reid (507 strain); S. siamkayai Stock, Somsook and Reid (157 strain); S. feltiae Filipjev (A05 strains); Heterorhabditis bacteriophora Poinar (1743 strain); and H. indica Poinar, Karunakar and David (HAM-64 strain). Activity of all strains was determined at four different nematode densities in Petri dishes and in concrete containers. A significant nematode density effect was detected for all nematode species tested. Overall, Heterorhabditis bacteriophora, S. siamkayai, and S. pakistanense were among those that showed the highest virulence to pulse beetle larvae and adults. For all nematode species, the last larval stage of the pulse beetle seems to be more susceptible than the adult. LC(50) values in Petri dish and concrete containers were 14-340 IJs/larvae and 41-441 IJs/larvae, respectively, and 59-1376 IJs/adult and 170-684/adult, respectively.     

Differences between the pathogenic processes induced by Steinernema and Heterorhabditis (Nemata: Rhabditida) in Pseudaletia unipuncta (Insecta: Lepidoptera)

Larvae of Pseudaletia unipuncta are moderately susceptible to infections caused by entomopathogenic nematodes, being a desirable host to study pathogenic processes caused by Heterorhabditis bacteriophora, Steinernema carpocapsae, and Steinernema glaseri and their associated bacteria. The ability of the infective stage of these nematodes to invade hosts is quite different. S. carpocapsae invades the highest number of insects and presents the highest penetration rate, followed by H. bacteriophora. Regression analysis between the number of insects parasitized and the number of IJs counted per insect, over time, showed a high correlation for S. carpocapsae whereas for H. bacteriophora it was low. Dose-response was most evident at a concentration below 100 IJs per insect on H. bacteriophora, whereas on S. carpocapsae it was found for doses ranging from 100 to 2,000 IJs. Student's t test analysis of dose-response showed parallel, yet unequal, slopes for both strains of H. bacteriophora, whereas distinct regressions were obtained for S. carpocapsae and S. glaseri, thus, evidencing each species develop a distinct pathogenic process. Insects injected with Photorhabdus luminescens died within 50 h after injection, whereas those treated with X. nematophila died much later. Moreover, the mortality in insects exposed to H. bacteriophora complex and injected with P. luminescens was close, but insects injected with bacteria died faster. Insect mortality in treatments with complexes S. carpocapsae and S. glaseri was significantly higher than that which was observed in insects injected with symbiotic bacteria.     

Compatibility of entomopathogenic nematodes with fipronil

The survival and infectivity of infective juveniles (IJs) of three species of entomopathogenic nematodes, Steinernema carpocapsae Weiser, S. arenarium (Artyukhovsky) (Rhabditida: Steinernematidae) and Heterorhabditis bacteriophora Poinar (Rhabditida: Heterorhabditidae), were determined after exposure to different concentrations (250, 500, 1000 and 2000 ppm) of fipronil, an insecticide acting on the GABA receptors to block the chloride channel. Heterorhabditis bacteriophora was very tolerant to all concentrations of fipronil, with the highest mortality of 17% being observed at 2000 ppm of fipronil after 72 h exposure. Steinernema carpocapsae showed a similar response, with the highest mortality of 11.25% of IJs being observed after 72 h exposure to 2000 ppm of fipronil. Steinernema arenarium was, however, more sensitive to fipronil, and at 2000 ppm mortality rates of 94.6% and 100% were observed after 24 and 72 h, respectively. Fipronil had negligible effects on the infectivity of the three nematode species tested. The IJs which survive exposure to all concentrations of fipronil tested can infect and reproduce in Galleria larvae. The moderate effects on entomopathogenic nematodes of a lower fipronil concentration (250 ppm) and the field rates (12-60 ppm) of fipronil used as insecticide, suggest that direct mixing of entomopathogenic nematodes and fipronil at field rates is a viable integrated pest management option.     

Rapid age-related changes in infection behavior of entomopathogenic nematodes

Nonfeeding infective juvenile (IJ) entomopathogenic nematodes (EPNs) are used as biological agents to control soil-dwelling insects, but poor storage stability remains an obstacle to their widespread acceptance by distributors and growers as well as a frustration to researchers. Age is one factor contributing to variability in EPN efficacy. We hypothesized that age effects on the infectiousness of IJs would be evident within the length of time necessary for IJs to infect a host. The penetration behavior of "young" (<1-wk-old) and "old" (2- to 4-wk-old) Heterorhabditis bacteriophora (GPS 11 strain), Steinernema carpocapsae (All strain), and Steinernema feltiae (UK strain) IJs was evaluated during 5 "exposure periods" to the larvae of the wax moth, Galleria mellonella. Individual larvae were exposed to nematode-infested soil for exposure periods of 4, 8, 16, 32, and 64 hr. Cadavers were dissected after 72 hr, and the IJs that penetrated the larvae were counted. Larval mortality did not differ significantly between 72- and 144-hr "observation periods," or points at which larval mortality was noted, for any age class or species. However, age and species effects were noted in G. mellonella mortality and nematode penetration during shorter time periods. Initial mortality caused by S. carpocapsae and H. bacteriophora IJs declined with nematode age but increased with S. feltiae IJ age. Young S. carpocapsae IJs penetrated G. mellonella larvae at higher rates than old members of the species (27-45% vs. 1-4%). Conversely, old S. feltiae IJs had higher penetration rates than young IJs (approximately 8 to 57% vs. 4 to approximately 31%), whereas H. bacteriophora IJs had very low penetration rates regardless of age (3-5.6%). Our results show that the effect of age on IJ infectiousness can be detected in IJs aged only 2 wk by a 4-hr exposure period to G. mellonella. These results have important implications for storage and application of EPNs and suggest the possibility of shortening the time required to detect nematodes in the soil.     

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.     

Virulence of entomopathogenic nematodes to Diaprepes abbreviatus (Coleoptera: Curculionidae) in the laboratory

The Diaprepes root weevil, Diaprepes abbreviatus (L.) is the most severe weevil pest in Florida citrus. Entomopathogenic nematodes have effectively suppressed larval populations of D. abbreviatus. Our objective was to conduct a broad laboratory comparison of entomopathogenic nematodes for virulence toward larvae of D. abbreviatus. The study was conducted at three temperatures (20, 24, and 29 degrees C) and included nine entomopathogenic species and 17 strains: Heterorhabditis bacteriophora Poinar (Baine, NJl, Hb, Hbl, HP88, and Lewiston strains), H. indica Poinar, Karunakar & David (original and Homl strains), H. marelatus Liu & Berry (IN and Point Reyes strains), H. megidis Poinar, Jackson & Klein (UK21l strain), H. zealandica Poinar (NZH3 strain), Steinernema riobrave Cabanillas, Poinar & Raulston (355 strain), S. carpocapsae (Weiser) (All strain), S. feltiae (Filipjev) (SN and UK76 strains), and S. glaseri (Steiner) (NJ43 strain). At 20 degrees C, the greatest mortality was caused by S. riobrave although it was not significantly greater than H. bacteriophora (Baine), H. bacteriophora (Hb), H. bacteriophora (Hbl), and H. indica (original). At 24 and 29 degrees C, S. riobrave caused greater larval mortality than other nematodes tested. Two strains of H. indica, H. bacteriophora (Baine), and S. glaseri were next in terms of virulence at 29 degrees C. Our results suggest that S. riobrave has the greatest potential for control of D. abbreviatus.