Susceptibility of the boll weevil to Steinernema riobrave and other entomopathogenic nematodes

The susceptibility of the boll weevil (BW), Anthonomus grandis Boheman, to Steinernema riobrave and other nematode species in petri dishes, soil (Hidalgo sandy clay loam), and cotton bolls and squares was investigated. Third instar weevils were susceptible to entomopathogenic nematode (EN) species and strains in petri dish bioassays at 30 degrees C. Lower LC(50)'s occurred with S. riobrave TX- 355 (2 nematodes per weevil), S. glaseri NC (3), Heterorhabditis indicus HOM-1 (5), and H. bacteriophora HbL (7) than H. bacteriophora IN (13), S. riobrave TX (14), and H. bacteriophora HP88 (21). When infective juveniles (IJs) of S. riobrave were applied to weevils on filter paper at 25 degrees C, the LC(50) of S. riobrave TX for first, second, and third instars, pupae, and 1-day-old and 10-days-old adult weevils were 4, 5, 4, 12, 13, and 11IJs per weevil, respectively. The mean time to death, from lowest to highest concentration, for the first instar (2.07 and 1.27days) and second instar (2.55 and 1.39days) weevils were faster than older weevil stages. But, at concentrations of 50 and 100IJs/weevil, the mean time to death for the third instar, pupa and adult weevils were similar (1.84 and 2.67days). One hundred percent weevil mortality (all weevil stages) occurred 3days after exposure to 100IJs per weevil. Invasion efficiency rankings for nematode concentration were inconsistent and changed with weevil stage from 15 to 100% when weevils were exposed to 100 and 1IJs/weevil, respectively. However, there was a consistent relationship between male:female nematode sex ratio (1:1.6) and nematode concentration in all infected weevil stages. Nematode production per weevil cadaver increased with increased nematode concentrations. The overall mean yield of nematodes per weevil was 7680IJs. In potted soil experiments (30 degrees C), nematode concentration and soil moisture greatly influenced the nematode efficacy. At the most effective concentrations of 200,000 and 400,000IJs/m(2) in buried bolls or squares, higher insect mortalities resulted in pots with 20% soil moisture either in bolls (94 and 97% parasitism) or squares (92 and 100% parasitism) than those of 10% soil moisture in bolls (44 and 58% parasitism) or squares (0 and 13% parasitism). Similar results were obtained when nematodes were sprayed on the bolls and squares on the soil surface. This paper presents the first data on the efficacy of S. riobrave against the boll weevil, establishes the potential of EN to control the BW inside abscised squares and bolls that lay on the ground or buried in the soil.     

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.     

Impact of the host cadaver on survival and infectivity of entomopathogenic nematodes (Rhabditida: Steinernematidae and Heterorhabditidae) under desiccating conditions

Entomopathogenic nematode species of Steinernema carpocapsae, Steinernema riobrave, or Heterorhabditis bacteriophora were used to compare survival and infectivity among infective juveniles (IJs) emerging in water from hosts in White traps (treatment a), emerging in sand from hosts placed in sand (treatment c), and emerging from hosts placed on a mesh suspended over sand (treatment m). Nematode survival and infectivity was recorded in sand at three-day intervals during 21 days of storage in desiccators at 75% relative humidity and 25 degrees C. Infectivity was measured by exposing 5 Galleria mellonella for 16 h to IJs. Treatment did not affect percent survival of H. bacteriophora IJs. Percent survival of S. riobrave and S. carpocapsae IJs was lowest in treatment a. Across all treatments, by 10 days after the beginning of the experiments, IJ survival declined to 93, 43, and 28% of levels on day 1 for H. bacteriophora, S. riobrave, and S. carpocapsae, respectively. For the three treatments, infection rate over time was described by a negative exponential function for S. riobrave and S. carpocapsae and by a sigmoid function for H. bacteriophora.     

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.     

Entomopathogenic nematodes to control black vine weevil (Coleoptera: Curculionidae) on strawberry.

We investigated the potential of heterorhabditid nematodes to control larvae of the black vine weevil, Otiorhynchus sulcatus (F.), in 2 field experiments in commercial strawberry plantings. In both experiments, nematodes were applied directly onto the straw mulch, or onto the soil after temporary removal of the mulch. Heterorhabditis marelatus Lui & Berry (Rhabditida: Heterorhabditidae) reduced numbers of weevil larvae and the percentage of plants infested in both experiments, irrespective of straw removal. In the 1st field experiment, a sponge-packed H. marelatus formulation produced lower numbers of O. sulcatus larvae per strawberry plant (mean O. sulcatus larvae per plant = 0.7) and proportion of infested plants (42%) compared with a vermiculite formulation (mean O. sulcatus larvae per plant = 1.8, proportion infested plants 67%) and an untreated control (mean O. sulcatus larvae per plant = 1.9, proportion infested plants 75%). In the first 2 wk after application, more H. marelatus were found in soil samples collected from plots treated with sponge-packed nematodes, than from plots treated with vermiculite-formulated nematodes. In the 2nd field experiment, sponge-packed formulations of H. bacteriophora Poinar (Rhabditida: Heterorhabditidae) and H. marelatus were tested. H. marelatus caused a reduction in both numbers of weevil larvae (mean O. sulcatus larvae per plant = 0.1) and proportion of infested plants (9%) but H. bacteriophora did not (mean O. sulcatus larvae per plant = 0.45, proportion infested plants 34%). More H. bacteriophora were recovered from soil samples than H. marelatus during the first 7 d of this experiment. However, laboratory studies revealed no difference in the persistence of these 2 nematodes in sand.     

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.     

Efficacy of Heterorhabditis baujardi LPP7 (Nematoda: Rhabditida) applied in Galleria mellonella (Lepidoptera: Pyralidae) insect cadavers to Conotrachelus psidii, (Coleoptera: Curculionidae) larvae

The guava weevil, Conotrachelus psidii, is a major pest of guava in Brazil causing severe reduction in fruit quality. We assessed its susceptibility to Heterhorhabditis baujardi LPP7 infective juveniles (IJs) in the greenhouse and under field conditions applying the nematodes in cadavers of seventh instar Galleria mellonella larvae. Field persistence of these nematodes in the soil was evaluated through G. mellonella-baiting. Insect cadaver concentrations of 2, 4 and 6 applied in pots in the greenhouse experiment caused significant mortality compared to the control. Significance differences were observed in the field between control and treatments only when six cadavers per 0.25 m² were applied. Infective juveniles from the cadavers persisted 6 weeks after application in the field, but decreased greatly thereafter. Our work demonstrates that H. baujardi LPP7 IJs emerging from G. mellonella cadavers can be efficacious against guava weevil fourth instar larvae. Also, we demonstrated the long-term persistence of IJs in the soil.     

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.     

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.     

Comparison of Bioassays to Measure Virulence of Different Entomopathogenic Nematodes

Five bioassays were compared for their usefulness to determine the virulence of four nematode strains. The objective of this study was to develop standard assays for particular nematode species. In all assays, the nematodes Steinernema feltiae (strain UK), S. riobravis, S. scapterisci Argentina and Heterorhabditis bacteriophora HP88 were exposed to Galleria mellonella larvae. All bioassays except the sand column assay were conducted in multi-well plastic dishes. In the penetration rate assay, the number of individual nematodes invading the insect was determined after a 48-h exposure to 200 infective juveniles (IJs). In the one-on-one assay, each larva was exposed to an individual nematode for 72 h before insect mortality was recorded. In the exposure time assay, insect mortality was recorded after exposure to 200 IJs for variable time periods. The dose-response assay involved exposing larvae to different nematode concentrations over the range 1-200 IJs/insect and recording mortality every 24 h for a 96-h period. In the sand columns assay, insects were placed in the bottom of a plastic cylinder filled with sand. Nematodes were applied on top of the sand and insect mortality was determined after IJs had migrated through the cylinder. The highest mortality level in the sand column assay was obtained with IJs of S. feltiae followed by H. bacteriophora; treatments with S. riobravis and S. scapterisci produced low levels of insect mortality. In the other four assays, S riobravis was the most virulent, followed by S. feltiae, H. bacteriophora and S. scapterisci. In the exposure time assay, rapid mortality was achieved when the insects were exposed to S. feltiae and S. riobravis. For these nematode species, a gradual increase in the number of individuals which penetrated into cadavers was recorded. Conversely, the number of nematodes in the cadavers of insects infected by H. bacteriophora and S. scapterisci remained low during the entire exposure period. In this assay, exposing the insects to these nematodes resulted in a gradual increase in mortality. In the dose-response assay, complete separation among nematode species was obtained only after 48 h of incubation at a concentration of 15 IJs/insect. LD and LD values were calculated from 50 90 dose-response assay data. However, these values did not indicate differences among the different nematode species. The present study demonstrated the variation in entomopathogenic nematode performance in different bioassays and supports the notion that one common bioassay cannot be used as a universal measure of virulence for all species and strains because nematodes differ in their behavior. Furthermore, particular assays should be used for different purposes. To select a specific population for use against a particular insect, assays that are more laborious but which simulate natural environmental conditions (e.g. the sand column assay) or invasion by the nematode (e.g. the penetration rate assay) should be considered. In cases where commercial production batches of the same nematode strains are compared, simple and fast assays are needed (e.g. the one-on-one and exposure time assays). Further studies are needed to determine the relationships between data obtained in each assay and nematode efficacy in the field.     

Formulation of entomopathogenic nematode-infected cadavers

Entomopathogenic nematodes are commercially applied in aqueous suspension. These biocontrol agents may also be applied in nematode-infected insect cadavers, but this approach may entail problems in storage and ease of handling. We determined the feasibility of formulating nematode-infected insect cadavers to overcome these hindrances. All experiments were conducted with Heterorhabditis bacteriophora Poinar and Galleria mellonella (L.). Nonformulated cadavers were used as controls. Of 19 formulations tested (including combinations of starches, flours, clays, etc.) 1 (starch-clay combination) was found to adhere to the cadaver and to have no significant deleterious effects on nematode reproduction and infectivity; other formulations exhibited poor adhesion or reduced nematode reproduction. Two formulations enabled cadavers to be partially desiccated without affecting reproduction; other formulations and nonformulated cadavers exhibited reduced reproduction upon desiccation. Four-day-old cadavers were more amenable to desiccation than 8-day-old cadavers. Formulated cadavers were more resistant to rupturing and sticking together during agitation than nonformulated cadavers.     

Influences of host size and host species on theinfectivity and development of Heterorhabditismegidis (strain NLH-E87.3)

The infectivity, time to first emergence of infective juveniles (IJs), total number of IJs per insect and IJs body length of the entomopathogenic nematode Heterorhabditis megidis (strain NLH-E87.3) after development in larvae of two insect hosts, Galleria mellonella (greater wax moth) and Otiorhynchus sulcatus (vine weevil) was studied. At a dose of 30 IJs, larvae of G. mellonella show to be significantly more susceptible than O. sulcatus larvae. At a dose of one IJ, vine weevil larvae were more susceptible. The number of invading infective juveniles (IJs) increased with host size while the host mortality at a dose of one IJ decreased with the increase of host size. Time to first emergence was longer at a dose of one IJ per larva and increased with the increase of host size in both insect species. Reproduction of IJs differed between host species, host sizes and doses of nematodes. Generally, the IJs body size increased with an increasing host size. The longest infective juveniles were produced at the lowest IJ doses. Results are discussed in relation to the influence of different host species and their different sizes on the performance of H. megidis (strain NLH-E87.3) as a biological control agent.     

Field evaluation of entomopathogenic nematodes for the biological control of the annual bluegrass weevil,Listronotus maculicollis (Coleoptera: Curculionidae), in golf course turfgrass

The ability of entomopathogenic nematodes to suppress larval populations of the annual bluegrass weevil, Listronotus maculicollis, was investigated under field conditions over a 3-year period (2006–2008). Combination of nematode species, application rate and timing produced strong numerical yet few statistically significant reductions. Steinernema carpocapsae Weiser, S. feltiae Filipjev, and Heterorhabditis bacteriophora Poinar applied at 2.5×10⁹ IJs/ha reduced first generation late instars between 69 and 94% in at least one field trial. Steinernema feltiae provided a high level of control (94%) to low densities (~20 larvae per 0.09 m²), but gave inadequate control for higher densities (24 and 50% suppression). No significant differences were found among treatment timings. However, applications timed to coincide with the peak of larvae entering the soil (fourth instars) generally performed better than applications made prior to (preemptive) or after the majority of the population advanced from the fourth instar. Nematode populations declined sharply between 0 and 14 days after treatment (DAT). Although nematode populations later increased (at 28 DAT), indicating an ability to recycle within hosts in the environment, they were nearly undetectable 56 DAT when the second generation host larvae were present in the soil. Applying commercially available nematode species at standard field rates cannot reliably reduce L. maculicollis immature densities on golf courses, nor will single applications suppress multiple generations. Future research will need to identify application strategies to improve biocontrol consistency.     

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.     

Biological control agents for white grubs (Coleoptera: Scarabaeidae) in anticipation of the establishment of the Japanese beetle in California

We tested biological control agents for the control of 3rd-instar scarab turfgrass pests, both for the masked chafer Cyclocephala hirta LeConte and the Japanese beetle, Popillia japonica Newman. The former species is endemic in California whereas the latter, although not yet established, constitutes a permanent serious threat to agriculture and horticulture in California. We conducted experiments using C. hirta in California and P. japonica in New Jersey. A field trial conducted in 2 different California turfgrass sites compared the field persistence in the absence of hosts of Bacillus thuringiensis Berliner subspecies japonensis Buibui strain, the milky disease bacterium, Paenibacillus (=Bacillus) popilliae (Dutky), and the entomopathogenic nematodes Steinernema kushidai Mamiya and Heterorhabditis bacteriophora Poinar to that of the organophosphate diazinon. Soil samples taken 0-70 d after applications were bio-assayed with P. japonica. Only diazinon and the entomopathogenic nematode S. kushidai caused substantial mortality and S. kushidai activity persisted significantly longer than diazinon activity. In greenhouse experiments, combinations of entomopathogenic nematode species usually resulted in additive mortality of scarab larvae. Combinations of S. kushidai and diazinon also resulted in additive mortality. In field trials, the efficacy of H. bacteriophora and especially S. kushidai and S. glaseri, was comparable to that of diazinon over 14-18 d. However, it is likely that at least S. kushidai would have outperformed diazinon over an extended period because of its longer persistence and potential for recycling in the hosts. S. kushidai, should it become commercially available, deserves further examination as an alternative to chemical white grub control especially as a highly compatible component of sustainable turfgrass management.     

Effect of insect cadaver desiccation and soil water potential during rehydration on entomopathogenic nematode (Rhabditida: Steinernematidae and Heterorhabditidae) production and virulence

We examined the influence of insect cadaver desiccation on the virulence and production of entomopathogenic nematodes (EPNs), common natural enemies of many soil-dwelling insects. EPNs are often used in biological control, and we investigated the feasibility of applying EPNs within desiccated insect cadavers. Desiccation studies were conducted using the factitious host, Galleria mellonella (Lepidoptera: Pyralidae, wax moth larvae) and three EPN species (Heterorhabditis bacteriophora ‘HB1’, Steinernema carpocapsae ‘All’, and Steinernema riobrave). Weights of individual insect cadavers were tracked daily during the desiccation process, and cohorts were placed into emergence traps when average mass losses reached 50%, 60%, and 70% levels. We tracked the proportion of insect cadavers producing infective juveniles (IJs), the number and virulence of IJs produced from desiccated insect cadavers, and the influence of soil water potentials on IJ production of desiccated insect cadavers. We observed apparent differences in the desiccation rate of the insect cadavers among the three species, as well as apparent differences among the three species in both the proportion of insect cadavers producing IJs and IJ production per insect cadaver. Exposure of desiccated insect cadavers to water potentials greater than −2.75 kPa stimulated IJ emergence. Among the nematode species examined, H. bacteriophora exhibited lower proportions of desiccated insect cadavers producing IJs than the other two species. Desiccation significantly reduced the number of IJs produced from insect cadavers. At the 60% mass loss level, however, desiccated insect cadavers from each of the three species successfully produced IJs when exposed to moist sand, suggesting that insect cadaver desiccation may be a useful approach for biological control of soil insect pests.     

Steinernema scarabaei, an entomopathogenic nematode for control of the European chafer

A new entomopathogenic nematode species, Steinernema scarabaei, was evaluated for efficacy against two white grub species, the European chafer, Rhizotrogus majalis, and the Japanese beetle, Popillia japonica, in laboratory, greenhouse, and field trials. In laboratory assays, S. scarabaei caused greater mortality than Heterorhabditis bacteriophora. S. scarabaei was highly virulent with an LC₅₀ of 5.5–6.0 and 5.7 infective juveniles (IJs) per third-instar larva in R. majalis and P. japonica, respectively. In a greenhouse trial, S. scarabaei provided greater mortality of R. majalis at all application rates (0.156–1.25 × 10⁹ IJs/ha) than Steinernema glaseri and H. bacteriophora (both at 1.25 × 10⁹ IJs/ha). Combination of imidacloprid and S. scarabaei resulted in an antagonistic interaction. In a fall field trial, S. scarabaei provided 88 and 75% control of R. majalis at 2.5 × 10⁹ and 10⁹ IJs/ha, respectively, and 54% control of P. japonica at 10⁹ IJs/ha; H. bacteriophora had no effect on mortality of either white grub species. In a spring field trial, unusually cool temperatures impeded nematode activity. Against R. majalis, S. scarabaei provided moderate control (56–59%), whereas Heterorhabditis marelatus provided no control. Mortality of P. japonica was moderate (49–66%) in both S. scarabaei and H. marelatus treatments. Overwinter persistence of S. scarabaei activity was demonstrated in a spring assay of soil from fall treated plots in which nematode infection was absent from control plots and present in treated plots.     

Biological and chemical control of the Asiatic garden beetle, Maladera castanea (Coleoptera: Scarabaeidae)

The efficacy of chemical and biological control agents against larvae of the Asiatic garden beetle, Maladera castanea (Arrow), in turfgrass under laboratory, greenhouse, and field conditions were determined. In field trials where insecticides were applied preventively against eggs and young larvae, the molt-accelerating compound halofenozide and the neonicotinoids imidacloprid and thiamethoxam were ineffective, whereas another neonicotinoid, clothianidin, provided 62-93% control. In greenhouse experiments against third instars in pots, the carbamate insecticide carbaryl was ineffective, whereas the organophosphate trichlorfon provided 71-83% control. In laboratory, greenhouse, and field experiments, the entomopathogenic nematode Heterorhabditis bacteriophora Poinar and Steinernema glaseri Steiner (not tested in the field) were ineffective against third instars, whereas S. scarabaei Stock & Koppenh?fer provided excellent control. In microplot field experiments at a rate of 2.5 x 10(9) infective juveniles per ha, H. bacteriophora provided 12-33% control and S. scarabaei 71-86% control. Combinations of S. scarabaei and imidacloprid did not provide more control of third instars compared with S. scarabaei alone.     

Efficacy of the entomopathogenic nematodes Steinernema kraussei and Heterorhabditis megidis against the black vine weevil Otiorhynchus sulcatus in open field‐grown strawberry plants

• 1 Entomopathogenic nematodes are commercially available for inundative biological control of many insects, including the black vine weevil Otiorhynchus sulcatus (F.) (Coleoptera: Curculionidae). Currently, there is a lack of commercial application tests in field‐grown crops comparing the efficacy of different species of entomopathogenic nematodes.
• 2 Field trials were carried out under different growing conditions in Ireland and Norway to evaluate the efficacy of two commercially available nematode species on the market for control of the black vine weevil Heterorhabditis megidis and Steinernema kraussei.
• 3 Heterorhabditis megidis was evaluated not only at temperatures ideal for this species (soil temperatures above 10 °C), but also in the low temperature trials with S. kraussei as a ‘positive control’. Steinernema kraussei is sold as a cold active product and was therefore evaluated at low soil temperatures (below 10 °C).
• 4 The overall results indicated that H. megidis was effective as long as temperatures were optimum (not dropping below 10 °C). For S. kraussei, the results obtained were rather disappointing, where control barely reached 50% in the trial with the coldest temperature. Temperature and soil type appeared to be a major limiting factor for the efficacy of both nematode species.
• 5 On the basis of the results and experience obtained in these trials, the future implications for biological control of O. sulcatus with entomopathogenic nematodes in commercial field‐grown strawberry production are discussed.

     

Assessing the Potential of Entomopathogenic Nematodes to Control the Grape Root Borer Vitacea polistiformis (Lepidoptera: Sesiidae) Through Laboratory and Greenhouse Bioassays

Seventeen entomopathogenic nematode species and strains were evaluated for virulence to the grape root borer, Vitacea polistiformis (Harris) in laboratory and greenhouse bioassays. Heterohabditis bacteriophora strain GPS11 and H. zealandica strain X1 produced a larval mortality rate of over 85% of larvae embedded in the root cambium in laboratory bioassays. The nematode species H. marelata and H. bacteriophora strain Oswego produced mortality rates of over 75%. Of the Steinernema species tested, S. carpocapsae strain 'All' performed the best with a mortality rate of 69%. All other nematode species and strains tested, with the exception of S. bicornutum , produced some degree of larval mortality. In the greenhouse bioassays, 93% control was achieved with H. zealandica strain X1 applied at 4 ×109 infective juveniles (IJs) acre1 -1 (9.88 ×10 9 IJs ha -1 ). H. bacteriophora strain GPS11 successfully reproduced in grape root borer larvae. The numbers of IJs produced within infected larvae were related to larval size. The survival rate of neonate larvae on grape root sections was 61%, which thus provides a means to rear the neonate larvae for bioassays.