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.     

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     

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.     

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.     

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.     

Susceptibility of Mocis latipes (Lepidoptera: Noctuidae) to Heterorhabditis bacteriophora (Rhabditida: Heterorhabditidae)

The susceptibility of larvae, prepupae, and pupae of the grass looper Mocis latipes (Guenée) to the entomopathogenic nematode Heterorhabditis bacteriophora (Poinar) NC strain was evaluated under laboratory conditions. Concentrations of 0, 5, 10, 20, 40, 60, and 120 nematodes per larva, applied in 1 ml of sterile-distilled water, were bioassayed, applying them to groups of 20 individuals of each instar, prepupa or pupa. Mortality was recorded daily for 5 d. All instars and the prepupal stage were the most susceptible to H. bacteriophora. Mortality ranged from 22.5 to 100%. Prepupae had 97.5-100% mortality starting at 10 nematodes per prepupa. Pupal mortality ranged from 27.5 to 41.3% as nematode concentration was increased. H. bacteriophora presented LC50 values that ranged between 5.26 and 37.66 nematodes per larva and LT50 values that ranged between 1.5 and 4.3 d. Results of this study suggest that H. bacteriophora has potential as a biocontrol agent against M. latipes.     

Entomopathogenic nematodes for biological control of the leafminer,Liriomyza trifolii (Dipt.: Agromyzidae)

In the laboratory, mortality rates of the agromyzid leafminer larvae,Liriomyza trifolii (Burgess), ranged from 48 to 98% by 20 strains and/or species of steinernematid and heterorhabditid nematodes. In the greenhouse, abamectin provided superior control of larval leafminers, killing 100% of them as compared withSteinernema carpocapsae (Weiser) All strain (24 to 43% leafminer mortality) orS. carpocapsae Liriomyza-selected strain (8 to 44% leafminer mortality); the maximum relative humidity (r.h.) ranged between 81 and 91% and the minimum r.h. between 50 and 70%. In the foghouse under high r.h., the commercially available All strain and the Hawaiian isolate ofS. feltiae (Filipjev) MG-14 strain caused 69 and 67% mean mortality, respectively. There was a significant correlation (P<0.01) between nematode mortality of leafminers and r.h., including the mean, standard deviation, and minimum r.h. during the 48 h after treatment. Average r.h. >92% with a standard deviation of <9% r.h. and a minimum of 72% r.h. providedS. carpocapsae All strain mortality rates of leafminers >65%. The major constraint against the use of nematodes against leafminers in the foliar environment is low r.h. The use of nematodes againstL. trifolii can be successful if the r.h. remains high and if nematodes enter leafmines before desiccation, and the nematodes should be integrated with chemical insecticides such as abamectin to manage pesticide resistance inL. trifolii.     

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.     

Infectivity of Four Species of Nematodes (Rhabditoidea: Steinernematidae, Heterorhabditidae) to the Asian Longhorn Beetle, Anoplophora glabripennis (Motchulsky) (Coleoptera: Cerambycidae)

Four species of entomopathogenic nematodes, Steinernema carpocapsae , Heterorhabditis bacteriophora , H. indica and H. marelatus , were tested for their ability to kill and reproduce in larvae of the Asian longhorn beetle, Anoplophora glabripennis (Motchulsky). The larvae were permissive to all four species but mortality was higher and production of infective juveniles was greater for S. carpocapsae and H. marelatus . The lethal dosage of H. marelatus was determined to be 19 infective juveniles for second and third instar larvae and 347 infective juveniles for fourth and fifth instar larvae. H. marelatus infective juveniles, applied via sponges to oviposition sites on cut logs, located and killed host larvae within 30 cm galleries and reproduced successfully in several of the larvae.     

Parasitism of subterranean termites (Isoptera: Rhinotermitidae: Termitidae) by entomopathogenic nematodes (Rhabditida: Steinernematidae; Heterorhabditidae)

In laboratory bioassays, Steinernema riobrave Cabanillas, Poinar and Raulston (355 strain), Steinernema carpocapsae (Weiser) (Mexican 33 strain), Steinernemafeltiae (Filipjev) (UK76 strain), and Heterorhabditis bacteriophora Poinar (HP88 strain) were all capable of infecting and killing three termite species, Heterotermes aureus (Snyder), Gnathamitermes perplexus (Banks), and Reticulitermes flavipes (Kollar) in laboratory sand assays. S. riobrave and S. feltiae caused low levels of Reticulitermes virginicus (Banks) mortality under the same conditions. At 22 degrees C, significant mortality (> or = 80%) of worker H. aureus and G. perplexus was caused by S. riobrave, in sand assays, indicating the need for further study. Because of the short assay time (3 d maximum), reproduction of the nematodes in the target host species was not recorded. All nematode species were observed to develop to fourth-stage juveniles, preadult stages, or adults in all termite species with the exception of R. virginicus. Only S. riobrave developed in R. virginicus. Nematode concentration and incubation time had significant effects on the mortality of worker H. aureus. S. riobrave consistently generated the highest infection levels and mortality of H. aureus in sand assays.     

Efficacy of entomopathogenic nematodes against neonate larvae of <Emphasis Type="Italic">Capnodis tenebrionis</Emphasis> (L.) (Coleoptera: Buprestidae) in laboratory trials

The efficacy of five entomopathogenic nematode strains of the families Steinernematidae and Heterorhabditidae was tested against the neonate larvae of Capnodis tenebrionis. The nematode strains screened included two of Steinernema carpocapsae (Exhibit and M137), and one each of S. feltiae (S6), S. arenarium (S2), and Heterorhanditis bacteriophora (P4). Exposure of neonate larvae of Capnodis to 10 and 150 infective juveniles (IJs) per larva (equivalent to 3 and 48 IJs/cm² respectively) in test tubes with sterile sand, resulted in mortality between 60–91% and 96–100%, respectively. At a concentration of 150 IJs/larva, all of the nematode strains were highly virulent. Both S. carpocapsae strains (Exhibit and M137) caused infection and mortality to larvae more quickly than the other strains. However, at a lower concentration assay (10 IJs/larva), S. arenarium was the most virulent strain. The penetration rate as an indicator of entomopathogenic nematode infection was also evaluated. The highest value was recorded for S. arenarium (36%), followed by H. bacteriophora (30.6%), S. feltiae (23.1%), and S. carpocapsae (20.7%).     

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.     

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.     

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.     

Pathogenicity caused by high virulent and low virulent strains of Steinernema carpocapsae to Galleria mellonella

Steinernema carpocapsae is an entomopathogenic nematode associated with a symbiotic bacterium, Xenorhabdus nematophilus. Both components of the complex participate in a pathogenic process in insects. This has raised two questions: how much does each one participate, and what mechanisms are involved? In this paper we compare the virulence of two strains of S. carpocapsae: a high virulent strain (Breton) and a low virulent strain (Az27), both of which are free of symbiotic bacteria. Breton and Az27 strains each one have similar ability to invade Galleria mellonella with median infectious times of 3.9 and 3.2 h, respectively. However, the LD(50) of the Breton and Az27 strains are 48.6 and 894.5 infective juveniles per insect, respectively. Breton strain takes 38 h to kill 100% of exposed insects, whereas Az27 takes three times longer. The lethal time of the low virulent strain in G. mellonella larvae is highly dependent on the number of nematodes which have penetrated the hemocelium, whereas it is not on the high virulent strain. Hemolymph patterns in SDS-PAGE of insects parasitized by the high virulent strain showed important differences in respect to the low virulent strain and control. Secretion/excretion products of the high virulent strain have important proteolytic activity as well as alpha-mannosidase and alpha-fucosidase activities, whereas, in secretion/excretion products of the avirulent strain, proteolytic activity was lower and alpha-mannosidase and alpha-fucosidase activities were undetected.     

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.     

Pathogenicity, development, and reproduction of Heterorhabditis bacteriophora and Steinernema carpocapsae under axenic in vivo conditions

Galleria mellonella larvae cultured axenically were treated with axenic dauer juveniles of Heterorhabditis bacteriophora and Steinernema carpocapsae. After 3 days S. carpocapsae had killed all insects, with 9.4 +/- 4.3 nematodes per larva. H. bacteriophora were unable to kill G. mellonella, although 13.3 +/- 6.4 nematodes per Galleria were found in the hemocoel. Invading nematodes of both strains recovered from the dauer stage. H. bacteriophora developed into hermaphrodites with eggs and J1 in the uterus and in the hemolymph of the living insects. Development beyond the J1 stage was not recorded. An injection of supernatants from different Photorhabdus luminescens cultures killed the insects but could not provide nutrients to support a further development. Only the injection of bacterial cells supported production of dauers in the axenic insects. Axenic S. carpocapsae developed to adults and produced offspring. After 3 weeks an average of 5275 nematodes per larva were counted, of which 6.7% were dauer juveniles, 39.2% other juvenile stages, 11.9% males, and 42.2% females. Compared to in vivo reproduction in the presence of the symbiotic bacterium Xenorhabdus nematophilus the dauer juvenile yields were low. Even after 5 weeks the percentage of dauer juveniles did not surpass 10%.     

Impact of Entomopathogenic Nematodes on Different Soil-dwelling Stages of Western Flower Thrips, Frankliniella occidentalis (Thysanoptera: Thripidae), in the Laboratory and Under Semi-field Conditions

The impact of entomopathogenic nematodes (EPN) on mortality of soil-dwelling stages of western flower thrips (WFT), Frankliniella occidentalis (Thysanoptera: Thripidae) with different insect stage combinations was studied in the laboratory and under semi-field conditions. In laboratory experiments, the efficacy of Steinernema feltiae strain Sylt (Rhabditida: Steinernematidae) at a concentration of 400 infective juveniles (IJs) cm -2 was tested against different proportions of soil-dwelling stages of WFT, i.e. late second instar larvae (L2), prepupae and pupae. Soil was used as the testing medium. S. feltiae significantly affected the mortality of all soil-dwelling life stages of WFT at all tested insect stage combinations. The proportion of late L2 in the population negatively correlated to EPN-induced mortality. WFT prepupa and pupa were similarly susceptible to S. feltiae and their proportion in the population did not affect the EPN-induced mortality under laboratory conditions. The highest mortality (80%) was recorded when the population consisted only of prepupae and/or pupae. In the semi-field study, the impact of S. feltiae , S. carpocapsae strain DD136 and Heterorhabditis bacteriophora strain HK3 (Rhabditida: Heterorhabditidae) ( H. bacteriophora ) at concentrations of 400 and 1000 IJs cm -2 was evaluated against WFT reared on green beans, Phaseolus vulgaris L., as host plant in pot experiments in a controlled climate chamber. All tested EPN strains at both dose rates significantly reduced the WFT populations. Up to 70% reduction of the WFT population was obtained at the higher EPN concentration.     

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.     

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.