Comparison of Two Steinernematid Species for Control of the Root Weevil Diaprepes abbreviatus

Steinernema carpocapsae Weiser All strain was compared to Steinernema riobravis Cabanillas, Poinar, and Raulston for control of the root weevil, Diaprepes abbreviatus (L.), in the laboratory and in potted citrus. In the laboratory bioassay, D. abbreviatus larvae were exposed to 30, 60, and 120 nematodes/cm³ in sand. Insect mortality 1 week after application was greater (P ≤ 0.05) for S. riobravis than for S. carpocapsae in the laboratory bioassay. In the greenhouse bioassay, D. abbreviatus larvae were exposed to 3 and 9 nematodes per cm³ of soil in potted citrus. Again, at each rate, mortality was greater (P ≤ 0.05) in pots treated with S. riobravis than in pots treated with S. carpocapsae. The results of this study suggest that S. riobravis is a better biological control agent against D. abbreviatus larvae in potted plants than S. carpocapsae.     

Effects of Culture Method and Formulation on the Virulence of Steinernema riobrave (Rhabditida: Steinernematidae) to Diaprepes abbreviatus (Coleoptera: Curculionidae)

The Diaprepes root weevil, Diaprepes abbreviatus, is a pest of vegetables, ornamental plants, sugarcane, and citrus in Florida and the Caribbean. The entomopathogenic nematode, Steinernema riobrave, can reduce larval populations of D. abbreviatus substantially. Efficacy of entomopathogenic nematodes, however, may be affected by culture method and formulation. Using D. abbreviatus as the host, we compared the efficacy of two commercial S. riobrave formulations, a liquid and a waterdispersible granule (WDG), with each other and with in vivo produced S. riobrave. Nematodes in the commercial formulations were produced in vitro through liquid fermentation; the in vivo nematodes were cultured in Galleria mellonella and applied in aqueous suspension. Laboratory experiments measured nematode virulence in plastic cups containing soil and seventh-eighth instar D. abbreviatus. One laboratory experiment was conducted using only fresh nematodes (less than 5 days old); another experiment included WDG nematodes that were stored for 25 days at 10 °C. Two field experiments were conducted in which nematodes were applied either to potted citrus (containing D. abbreviatus larvae) placed beneath mature citrus trees or to soil directly beneath the tree. In the latter experiment, efficacy was determined by measuring mortality of caged D. abbreviatus larvae that were buried beneath the soil surface prior to application. Mortality of D. abbreviatus treated with nematodes ranged from 80-98% and 50-75% in laboratory and field experiments, respectively. In all experiments, we did not detect any significant effects of culture method or formulation.     

Steinernema diaprepesi n. sp. (Rhabditida: Steinernematidae), a Parasite of the Citrus Root Weevil Diaprepes abbreviatus (L) (Coleoptera: Curculionidae)

A nematode collected from Diaprepes abbreviatus is identified and described as a new species, Steinernema diaprepesi n. sp. The new species is closely related to S. feltiae, S. glaseri, and S. oregonense and can be distinguished from these species by the following characteristics: Males: Spicule averaging 79 (71-90) µm and spicule shape; D% (distance from anterior end to excretory pore/ esophagus length × 100) about 80; the ratio SW (spicule length/anal body width) about 1.8. Females: Vulva with short, double- flapped epiptygma; tail terminus usually with 5 papillae-like structures. Infective juveniles: Body averaging 1,002 (880-1,133) µm, EP (distance from anterior end to excretory pore) = 74 (66-83) µm; tail length = 83 (65-91) µm, and E% (EP/tail length × 100) = 89.6 (78-114). Lateral field pattern variable, the formula for the arrangement of ridges from head to tail is: 2, 6, 7, 8, 4, 2. The portion with eight ridges is the longest. This new species can be differentiated further from three closest species (S. feltiae, S. glaseri, and S. oregonense) by characteristic sequences of their ITS regions, including sequence lengths, ratios of similarity, composition, and differences in base characters in sequence alignment.     

Estimating Sample Size and Persistence of Entomogenous Nematodes in Sandy Soils and Their Efficacy Against the Larvae of Diaprepes abbreviatus in Florida

In two studies to estimate sampling requirements for entomogenous nematodes in the field, highest persistence of Heterorhabditis bacteriophora after application occurred beneath the canopies of mature citrus trees. Nematode persistence declined with distance from the center-line of the tree row toward the row-middles. Immediately after nematode application to soil, 32 samples (15 cm deep, 2.5-cm diameter) beneath a single tree were required to derive 95% confidence intervals that were within 40% of mean nematode population density. The estimated probability of measuring the mean density within 40%, using 32 samples, declined to 88% at 2 days post-application and to 76% at 7 days. The persistence in soil of Steinernema carpocapsae, S. riobravis, and two formulations containing H. bacteriophora and their efficacy against the larvae of Diaprepes abbreviatus were compared in a grove of 4-year-old citrus trees. Within 6 days, the recovered population densities of all nematodes declined to <5% of levels on day 0. The recovery of H. bacteriophora during the first 2 weeks was lower than that of the other two species. Steinemema riobravis and both formulations of H. bacteriophora reduced recovery of D. abbreviatus by more than 90% and 50%, respectively. Steinernema carpocapsae did not affect population levels of the insect.     

Evaluation of the Spatial Pattern of Steinernema riobravis in Corn Plots

The vertical and horizontal spatial patterns of a naturally occurring population of the entomopathogenic nematode Steinernema riobravis (Rhabditida: Steinernematidae) were investigated in corn field soil by laboratory and field bioassays. This nematode appears to be endemic to the Lower Rio Grande Valley of Texas, where it was found parasitizing prepupae and pupae of both corn earworm, Helicoverpa zea, and fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae). Corn earworm prepupa was the bioassay host used to detect S. riobravis from soil in previously harvested corn plots. Steinernema riobravis occurred at soil depths of 5-30 cm. The maximum nematode density was in the upper 20 cm of soil, and the lowest density occurred at soil depth of 25-30 cm. The field and laboratory bioassays performed on the top 20 era of soil resulted in S. riobravis-infected corn earworm of 49 and 34%, respectively, whereas at 25-30 cm soil depths 11 and 4.5% of the H. zea were infected, respectively. The horizontal spatial pattern of this nematode was patchy or aggregated. Our study provides new information on the spatial pattern of S. riobravis in its natural habitat and indicates the need to augment its natural biocontrol efficacy.     

From Augmentation to Conservation of Entomopathogenic Nematodes: Trophic Cascades, Habitat Manipulation and Enhanced Biological Control of Diaprepes abbreviatus Root Weevils in Florida Citrus Groves

The use of entomopathogenic nematodes (EPN) for management of the root weevil, Diaprepes abbreviatus, in Florida citrus groves is considered a biological control success story and typically involves augmentation in which EPN are applied inundatively as biopesticides to quickly kill the pest. However, recent evidence indicates that efficacy of EPN applications in Florida citrus depends on soil type. They are very effective in the well drained coarse sands of the Central Ridge but often less so in poorly drained fine-textured soils of the Flatwoods. Moreover, groves on the Central Ridge can harbor rich communities of endemic EPN that might often suppress weevil populations below economic thresholds, whereas Flatwoods groves tend to have few endemic EPN and frequent weevil problems. Current research is examining the ecological dynamics of EPN in Florida citrus groves, the potential impact of EPN augmentation on soil food webs, especially endemic EPN, and whether habitat manipulation and inoculation strategies might be effective for conserving and enhancing EPN communities to achieve long-term control in problem areas. Conservation biological control could extend the usefulness of EPN in Florida citrus and be especially appropriate for groves with persistent weevil problems.     

Incidence of Endemic Entomopathogenic Nematodes Following Application of Steinernema riobrave for Control of Diaprepes abbreviatus

Control of Diaprepes abbreviatus by endemic and exotic entomopathogenic nematodes (EPN) was monitored during 2000-2001 in two citrus orchards in central Florida (Bartow and Poinciana). Caged sentinel insect larvae were buried beneath citrus trees for 7 days at 1 to 2-month intervals from April to October each year. At Bartow, the survey occurred in experimental plots that were (i) not treated with commercial EPN, (ii) treated twice annually since 1998 with commercially formulated Steinernema riobrave, or (iii) treated twice annually with S. riobrave and liquid fertilization (15 times/year) occurred in place of dry fertilizer (3 times/year) used in the other treatments. Four endemic EPN species, in addition to S. riobrave, were recovered from the sandy soil at Bartow: S. diaprepesi, Heterorhabditis zealandica, H. indica, and H. bacteriophora. Mean insect mortality in control plots was 39.4% (range = 13% to 74%), with seasonal maxima in May to July each year. Endemic EPN were recovered from 55% (range = 22% to 81%) of the cadavers each month. Total numbers of endemic EPN recovered in all plots during 2 years were directly related to the numbers of adult weevils (D. abbreviatus and Pachnaeus litus) captured in modified Tedder''s traps and inversely related to recovery of S. riobrave. Insect mortality was higher and cadavers containing endemic EPN were more numerous in untreated control plots than in S. riobrave-treated plots, except during months in which S. riobrave was applied. In treated plots, endemic EPN were recovered from cadavers at twice the rate of S. riobrave. Suppression of endemic EPN in plots treated with S. riobrave, combined with inferior persistence by the introduced species, may have attenuated the net efficacy of S. riobrave against D. abbreviatus. In contrast, H. indica was the only endemic nematode recovered from the sandy clay loam soil at Poinciana, where the average mortality of D. abbreviatus was 12% (range 3% to 20%) and incidence of H. indica did not exceed 8%. Results of these surveys suggest that the regional patterns in the abundance and damage to citrus caused by D. abbreviatus in Florida are regulated by endemic EPN and other soilborne enemies of the weevil.     

Competition Between Entomopathogenic and Free-Living Bactivorous Nematodes in Larvae of the Weevil Diaprepes abbreviatus

Field and laboratory experiments were conducted to determine the degree to which free-living, bactivorous nematodes (FLBN) are able to competitively displace entomopathogenic nematodes (EPN) from insect cadavers. Two hundred larvae of the insect Diaprepes abbreviatus were buried at regular intervals during 2 years in experimental plots that were untreated or treated twice annually with Steinernema riobrave. Larvae were recovered after 7 days, and nematodes emerging from cadavers during the next 30 days were identified. The monthly prevalence of FLBN was directly related to that of S. riobrave (r = 0.38; P = 0.001) but was not related to the prevalence of the endemic EPN, S. diaprepesi, Heterorhabditis zealandica, H. indica, or H. bacteriophora (r = 0.02; P = 0.80). In a second experiment, treatment of small field plots with S. riobrave increased the prevalence of insect cadavers in which only FLBN were detected compared to untreated controls (30% vs. 14%; P = 0.052), and increased numbers of FLBN per buried insect by more than 10-fold. In the laboratory, sand microcosms containing one D. abbreviatus larva were treated with (i) the FLBN, Pellioditis sp.; (ii) S. riobrave; (iii) S. riobrave + Pellioditis; or (iv) neither nematode. Insect mortality was higher in the presence of both nematodes (57%) than when S. riobrave was alone (42%) (P = 0.01). An average of 59.2 Pellioditis sp. g^-1 insect body weight emerged in the presence of S. riobrave, whereas 6.2 nematodes g^-1 insect were recovered in the absence of the EPN (P = 0.01). Pellioditis sp. reduced the number of S. riobrave per cadaver by 84%; (P = 0.03), and per available insect by 82% (P = 0.001), compared to S. riobrave alone. Population size of S. diaprepesi was not affected by Pellioditis sp. in experiments of the same design. Faster development (P = 0.05) and nutrient appropriation within the insect cadaver by S. diaprepesi compared to S. riobrave may increase the fitness of the former species to compete with Pellioditis sp. The results of these studies demonstrate the potential of FLBN to regulate population densities of EPN and to dampen estimates of EPN-induced mortality of insect pests in the field.     

Parasitism of Western Corn Rootworm Larvae and Pupae by Steinernema carpocapsae

Virulence and development of the insect-parasitic nematode, Steinernema carpocapsae (Weiser) (Mexican strain), were evaluated for the immature stages of the western corn rootworm, Diabrotica virgifera virgifera LeConte. Third instar rootworm larvae were five times more susceptible to nematode infection than second instar larvae and 75 times more susceptible than first instar larvae and pupae, based on laboratory bioassays. Rootworm eggs were not susceptible. Nematode development was observed in all susceptible rootworm stages, but a complete life cycle was observed only in second and third instar larvae and pupae. Nematode size was affected by rootworm stage; the smallest infective-stage nematodes were recovered from second instar rootworm larvae. Results of this study suggest that S. carpocapsae should be applied when second and third instar rootworm larvae are predominant in the field.     

Bionomics of a Phoretic Association Between Paenibacillus sp. and the Entomopathogenic Nematode Steinernema diaprepesi

Spores of an unidentified bacterium were discovered adhering to cuticles of third-stage infective juvenile (IJ) Steinernema diaprepesi endemic in a central Florida citrus orchard. The spores were cup-shaped, 5 to 6 mm in length, and contained a central endospore. Based on 16S rDNA gene sequencing, the bacterium is closely related to the insect pathogens Paenibacillus popilliae and P. lentimorbus. However, unlike the latter bacteria, the Paenibacillus sp. is non-fastidious and grew readily on several standard media. The bacterium did not attach to cuticles of several entomopathogenic or plant-parasitic nematodes tested, suggesting host specificity to S. diaprepesi. Attachment of Paenibacillus sp. to the third-stage cuticle of S. diaprepesi differed from Paenibacillus spp. associated with heterorhabditid entomopathogenic nematodes, which attach to the IJ sheath (second-stage cuticle). The inability to detect endospores within the body of S. diaprepesi indicates that the bacterial association with the nematode is phoretic. The Paenibacillus sp. showed limited virulence to Diaprepes abbreviatus, requiring inoculation of larvae with 108 spores to achieve death of the insect and reproduction of the bacterium. The effect of the bacterium on the nematode population biology was studied in 25-cm-long vertical sand columns. A single D. abbreviatus larva was confined below 15-cm depth, and the soil surface was inoculated with either spore-free or spore-encumbered IJ nematodes. After 7 days, the proportion of IJ below 5-cm depth was seven-fold greater for spore-free IJ than for spore-encumbered nematodes. Mortality of D. abbreviatus larvae was 72% greater (P <= 0.01) for spore-free compared to spore-encumbered S. diaprepesi. More than 5 times as many progeny IJs (P <= 0.01) were produced by spore-free compared to spore-encumbered nematodes. These data suggest that the bacterium is a component of the D. abbreviatus food web with some potential to regulate a natural enemy of the insect.     

Pathogenicity of Steinernema scapterisci to Selected Invertebrates

Steinernema scapterisci was more pathogenic to insects tested in the order Orthoptera than to those in the orders Lepidoptera or Hymenoptera; it was not pathogenic to earthworms. The nematode also infected and killed the mole crickets Scapteriscus acletus and S. vicinus when released four successive times at 10-day intervals in containers of soil infested with the nematode.     

Activity and Persistence of Steinernema carpocapsae and Spodoptera exigua Nuclear Polyhedrosis Virus against S. exigua Larvae on Soybean

Experiments were conducted to assess the effects of the entomopathogenic nematode Steinernema carpocapsae and Spodoptera exigua multinucleocapsid nuclear polyhedrosis virus (SeMNPV), alone and in combinations, on mortality of the beet armyworm, S. exigua, larvae on soybean. In 1991 tests, field-grown soybean plants were treated with S. carpocapsae at 0.3 and 0.6 nematodes/cm² of leaflet, SeMNPV at 20 and 40 polyhedral inclusion bodies (PIB)/cm², and all possible combinations. Treated leaflets were collected from plants and bioassayed with 5-day-old larvae. The combination of S. carpocapsae at 0.6 nematodes/cm² + SeMNPV at 40 PIB/cm² produced significantly higher larval mortality (61.7%) compared with either S. carpocapsae (24.8-35.1%) or SeMNPV (26.5-33.7%) alone. In 1992, similar tests were repeated using S. carpocapsae at 0.2 and 0.5 nematodes/cm², and SeMNPV at 14 and 35 PIB/cm². The combination of 0.5 nematodes/cm² + 35 PIB/cm² resulted in significantly higher larval mortality (64.0%) than either pathogen alone (41.5-49.0%). Steinernema carpocapsae and SeMNPV produced additive effects on beet arlnyworm mortality. Persistence of S. carpocapsae was 12-24 hours and SeMNPV was 96-120 hours on soybean.     

Transfer and fate of seminal fluid molecules in the beetle, Diaprepes abbreviatus: implications for the reproductive biology of a pest species

Molecules transferred from males to females via seminal fluids are important to the study of insect reproduction because they affect female physiology, reproductive behavior, and longevity. These molecules (seminal fluid molecules or SFMs) interest applied entomologists because of their potential use in insect control. SFMs are also interesting because of their relatively rapid evolution and important role in post-mating sexual selection. We studied SFMs in Diaprepes abbreviatus, a major pest of numerous plant species of economic importance. Using radiolabeled-methionine (35S), we found that D. abbreviatus males synthesized proteins de novo in their reproductive tissues after mating. Males that were fed radiolabeled methionine transferred radioactivity to females beginning within the first 10 min of mating. Male-derived substances are absorbed from the female's reproductive tract into the hemolymph and circulated throughout the body, but are found primarily in the eggs and ovaries. As a result, SFMs may be a useful means of both horizontal (to mates) and vertical transfer (to offspring) of control agents between conspecifics.     

Status of biological control by egg parasitoids of Diaprepes abbreviatus (Coleoptera: Curculionidae) in citrus in Florida and Puerto Rico

Eggs of Diaprepes abbreviatus (L.) were routinely monitored in citrus groves at ten locations in Florida during 1997 and 1998 to study egg parasitism. One citrus location was studied in Puerto Rico. No native parasitoids were recovered from 1,337 D. abbreviatus egg masses studied in Florida citrus. In contrast, an average of 35.5% (range 12.5 to 68.8%) parasitism of egg masses was reported in Puerto Rico. The parasitoids Aprostocetus gala, Horismenus spp, and Quadrastichus haitiensis were recovered from the eggs of D. abbreviatusfstudied in Puerto Rico. The Horismenus parasitoids were suspected hyperparasitoids. Releases of the parasitoid Ceratogramma etiennei from Guadeloupe were initiated during 1998 at each of the Florida research sites. By the end of 1998, C. etiennei had been recovered from D. abbreviatus eggs at two of nine locations in Florida citrus. The parasitoid was recovered from 1 of 34 egg masses at one of these locations during the month of September and from 3 of 34 egg masses at the other location during the month of November. Whether or not C. etiennei establishes itself at one or more locations in Florida remains to be seen.     

Biological Control of the Pecan Weevil,Curculio caryae (Coleoptera: Curculionidae), with Entomopathogenic Nematodes

Steinernema carpocapsae (Weiser) strain A11, S. feltiae (Filipjev) strain SN, and Heterorhabditis bacteriophora Poinar strains HP88 and Georgia were tested for their efficacy as biological control agents of the pecan weevil, Curculio caryae (Horn), in pecan orchard soil-profile containers under greenhouse conditions. Percentage C. caryae parasitism by S. carpocapsae and H. bacteriophora strain HP88 and Georgia was consistently poor when applied either prior to or following C. caryae entry into the soil, suggesting that these nematode species and (or) their enterobacteria are poor biological control agents of weevil larvae. Soil taken 21 days following application of S. carpocapsae or H. bacteriophora strain HP88 induced a low rate of infection of Galleria mellonella larvae, whereas soil that had been similarily treated with H. bacteriophora strain Georgia induced a moderate rate of infection. Percentage C. caryae parasitism by S. feltiae was consistently low when applied following C. caryae entry into the soil and was inconsistent when applied as a barrier prior to entry of weevil larvae into the soil. Soil taken 21 days following application of S. feltiae induced a high rate of infection of G. mellonella larvae.     

Effects of Pesta-Pelletized Steinernema carpocapsae (All) on Western Corn Rootworms and Colorado Potato Beetles

Pesta-pelletized Steinernema carpocapsae (All) nematodes were used in soil treatments in the greenhouse against larvae of Western corn rootworm and prepupae of Colorado potato beetle. The pesta-pellets delivered 100,000 living nematodes/g. Infective-stage nematodes and their associated bacteria survived the pesta-pellet process, emerged from the pellets in large numbers in the soil, and reduced adult emergence of both pest insects by more than 90%.     

Cryopreservation of Steinernema carpocapsae and Heterorhabditis bacteriophora

A method for the cryopreservation of third-stage infective juveniles (IJ) of Steinernema carpocapsae and Heterorhabiditis bacteriophora was developed. Cryoprotection was achieved by incubating the nematodes in 22% glycerol (S. carpocapsae) or 14% glycerol (H. bacteriophora) for 24 hours, followed by 70% methanol at 0 C for 10 minutes. The viability of S. carpocapsae frozen in liquid nitrogen as 20 μl volumes spread over cover slip glass was > 80%. Survival of H. bacteriophora frozen on glass varied from 10 to 60% but was improved to > 80% by replacing the glass with filter paper. Cryopreservation and storage of 1-ml aliqots of S. carpocapsae IJ resulted in > 50% survival after 8 months; pathogenicity was retained and normal in vitro development took place. Trehalose and glycerol levels increased and glycogen levels decreased during incubation of S. carpocapsae IJ in glycerol. Normal levels of trehalose, glycerol and glycogen were restored during post freezing rehydration.     

Discovery and characterization of chemical signals for citrus root weevil, Diaprepes abbreviatus

The tropical root weevil Diaprepes abbreviatus (L. 1758) (Coleoptera: Curculionidae) is a polyphagous insect from the Caribbean Islands and an invasive insect in the southern part of the United States where it is pest of citrus crops and ornamental trees. Adults feed upon foliage where aggregation, mating and oviposition take place. Here, the headspace volatiles from Citrus macrophylla Wester (Rutaceae), D. abbreviatus adults feeding on this plant, adults alone and adult feces, were collected by aeration and solid-phase microextraction (SPME) for analysis by gas chromatography-linked mass spectrometry (GC-MS). Electrophysiological responses of weevil antennal receptors to volatile headspace extracts and synthetic analogues were recorded by gas chromatography-linked electroantennographic detection (GC-EAD) and electroantennograms (EAGs). Antennal responses were recorded to the monoterpenes (R)-(−)-linalool, citronellal, nerol, citral, and geraniol; all present in the headspace of C. macrophylla. Antennal responses were also recorded to carvacrol, present in the headspace of adults and adult feces. The green leaf volatiles cis-3-hexen-1-ol and trans-2-hexen-1-ol, produced by other host plants, elicited reliable responses on the D. abbreviatus antenna. When comparing EAGs between (±)-linalool and (R)-(−)-linalool, no significant difference was found; responses to (R)-(+)-citronellal were larger than for (S)-(−)-citronellal. Among the individual compounds and blends tested using an open T-track dual choice olfactometer, only the blend of (±)-linalool, cis-3-hexen-1-ol and carvacrol (source dose 25:25:2.5 μg) elicited significant attraction of females, the same blend was repellent for males. The biologically active compounds found here likely play a role in host finding by D. abbreviatus and other interactions of the insect with its hostplant. Handling editor: Sam Cook     

Impact of a Nematode-parasitic Fungus on the Effectiveness of Entomopathogenic Nematodes

The impact of the nematode-parasitic fungus Hirsutella rhossiliensis on the effectiveness of Steinernema carpocapsae, S. glaseri, and Heterorhabditis bacteriophora against Galleria mellonella larvae was assessed in the laboratory. The presence of Hirsutella conidia on the third-stage (J3) cuticle of S. carpocapsae and H. bacteriophora interfered with infection of insect larvae. Conidia on the J3 cuticle of S. glaseri and on the ensheathing second-stage cuticle of H. bacteriophora did not reduce the nematodes'' ability to infect larvae. The LD₅₀ values for S. carpocapsae, S. glaseri, and H. bacteriophora in sand containing H. rhossiliensis were not different from those in sterilized sand when Galleria larvae were added at the same time as the nematodes. However, when Galleria larvae were added 3 days after the nematodes, the LD₅₀ of S. glaseri was higher in Hirsutella-infested sand than in sterilized sand, whereas the LD₅₀ of H. bacteriophora was the same in infested and sterilized sand. Although the LD₅₀ of S. carpocapsae was much higher in Hirsutella-infested sand than in sterilized sand, the data were too variable to detect a significant difference. These data suggest that H. bacteriophora may be more effective than Steinernema species at reducing insect pests in habitats with abundant nematode-parasitic fungi.     

Effect of Soil Moisture and a Surfactant on Entomopathogenic Nematode Suppression of the Pecan Weevil, Curculio caryae

Our overall goal was to investigate several aspects of pecan weevil, Curculio caryae, suppression with entomopathogenic nematodes. Specifically, our objectives were to: 1) determine optimum moisture levels for larval suppression, 2) determine suppression of adult C. caryae under field conditions, and 3) measure the effects of a surfactant on nematode efficacy. In the laboratory, virulence of Heterorhabditis megidis (UK211) and Steinernema carpocapsae (All) were tested in a loamy sand at gravimetric water contents of negative 0.01, 0.06, 0.3, 1.0, and 15 bars. Curculio caryae larval survival decreased as moisture levels increased. The nematode effect was most pronounced at –0.06 bars. At –0.01 bars, larval survival was ≤5% regardless of nematode presence, thus indicating that intense irrigation alone might reduce C. caryae populations. Overall, our results indicated no effect of a surfactant (Kinetic) on C. caryae suppression with entomopathogenic nematodes. In a greenhouse test, C. caryae larval survival was lower in all nematode treatments compared with the control, yet survival was lower in S. carpocapsae (Italian) and S. riobrave (7–12) treatments than in S. carpocapsae (Agriotos), S. carpocapsae (Mexican), and S. riobrave (355) treatments (survival was reduced to approximately 20% in the S. riobrave [7–12] treatment). A mixture of S. riobrave strains resulted in intermediate larval survival. In field experiments conducted over two consecutive years, S. riobrave (7–12) applications resulted in no observable control, and, although S. carpocapsae (Italian) provided some suppression, treatment effects were generally only detectable one day after treatment. Nematode strains possessing both high levels of virulence and a greater ability to withstand environmental conditions in the field need to be developed and tested.