HP88 Strain Research Articles

Susceptibility of Sap Beetles (Coleoptera: Nitidulidae) to Entomopathogenic Nematodes

Nitidulid beetles (Coleoptera) are considered to be serious pests of date palms throughout the world. They attack ripe fruit, causing it to rot, and damage is reflected in both reduced yield and lower fruit quality. The present study was aimed at an evaluation of the susceptibility to different sap beetles to entomopathogenic nematodes. We further tested nematode efficacy in pots filled with soil infested by third instar larvae of the two beetle species. In Petri dish assay, mortality levels of Carpophilus humeralis and C. hemipterus exposed to Heterorhabditis sp. IS-5 strain indicated that the latter is less susceptible to nematode infection. Exposure of both sap beetle species to different nematode strains gave moderate levels of mortality (35-65%) with the heterorhabditid strains HP88, IS-5 and IS-25. The IS-12 strain of Heterorhabditis sp. showed poor virulence (<35% mortality) against larvae of C. humeralis as well as larvae and pupae of C. humipterus. The nematode species S. riobrave showed moderate virulence (35-65%) mortality to larvae and pupae of S. humeralis as well as to larvae of C. hemipterus . Exposure of C. hemeralis to different concentrations of Heterorhabditis sp. IS-5 in pots containing soil resulted in high mortality (>65%). In contrast, the lower concentrations (500 and 1000 nematodes/pot) caused low mortality (35%) of C. hemipterus . Other heterorhabditid strains caused 95-100% mortality of C. humeralis in pot assay. The HP88 strain of H. bacteriophora and the Tx strain of Steinernema riobrave showed poor effectiveness. Incubation of different nematode strains with the C. humeralis larvae at high temperature (32 C) resulted in an increase in insect mortality with the IS-12 and IS-21 strains. Reduced mortality was recorded with the HP88 strain treatment at the higher temperature. The IS-5 and IS-12 strains were equally effective in all three soil types tested, whereas the IS-19 strain was more effective in the Almog type soil than in the others.

Differential susceptibility of Dysmicoccus vaccinii (Homoptera: Pseudococcidae) to entomopathogenic nematodes (Rhabditida: Heterorhabditidae and Steinernematidae).

The susceptibility of the mealy bug, Dysmicoccus vaccinii Miller & Polavarapu, to infection by various species and strains of entomopathogenic nematodes was investigated in laboratory sand-dish and sand-column assays. Steinernemo carpocapsae (Weiser) (All strain), S. feltiae (Filipjev) (AB [Australia] strain), and S. glaseri (Steiner) (NC strain) were ineffective against individual mealybugs in sand-dish assays conducted in small petri dishes (1 cm high by 3.5 cm diameter) at 25 degrees C with doses of infective juvenile nematodes ranging up to 500 or 1,000 infective juveniles and exposure periods up to 5 d. However, Heterorhabditis bacteriophora Poinar (HP88 strain and 2 New Jersey isolates). H. hawaiiensis Gardner, Stock & Kaya (MG-13 strain), and H. indicus Poinar, Karunakar & David (EMS-13 strain) induced significant mortality (65.0-90.0%) at doses as low as 100 infective juveniles and an exposure of 5 d. H. bacteriophora (HBNJ strain) was effective at doses of 500 and 1,000 infective juveniles but, together with H. zealandica Poinar (V16 strain) and 4 other H. bacteriophora isolates from New Jersey, was ineffective at doses of 100 infective juveniles. Removal of the waxy coating from the mealybugs did not influence susceptibility to H. bacteriophora (HP88 strain). In the sand-column assay (5.5 cm high by 5 cm diameter, 5-d exposure, 25 degrees C), which more closely resembles host-finding in the field, H. bacteriophora (HP88 strain) induced no significant mortality against individual mealybugs at doses of 100 infective juveniles but produced 93.8% mortality at 500 infective juveniles, whereas H. indicus (EMS-13 strain) induced 56.3 and 100% mortality at 100 and 500 infective juveniles, respectively. H. bacteriophora (HP88 strain and some New Jersey isolates), H. hawaiiensis (MG-13 strain), and H. indicus (EMS-13 strain) successfully reproduced in and emerged from mealybug cadavers. This study demonstrates strong variability in the susceptibility of D. vaccinii to different species and strains of entomopathogenic nematodes, and implicates certain heterorhabditids as promising candidates for the biological control of this insect.

Genetic Improvement of Heat Tolerance inHeterorhabditis bacteriophorathrough Hybridization

Abstract A trait for heat tolerance was transferred from the IS5 strain to the HP88 strain of Heterorhabditis bacteriophora Poinar. The transfer was accomplished by allowing the heat tolerant strain (IS5) to mate with the commercial strain (HP88). The hybrid nature of the progeny was confirmed using a marker mutant of the HP88 strain ( Hp-dpy-2 ) and by backcrossing. Progeny from the cross were screened for heat tolerance by measuring survival after 2 h exposure to 40°C. After three and six passages through Galleria mellonella (L.), survival of hybrid nematodes was significantly greater than survival of the HP88 strain and was similar to the survival of the IS5 strain. Fitness, in terms of virulence, reproduction and storage capacity was compared among the IS5, hybrid, and HP88 strains. At 32°C, the IS5 and hybrid strains caused mortality of G. mellonella at a faster rate than the HP88 strain. Similar to the IS5 strain, the hybrids exhibited sensitivity to cold. After 1 week of storage at 10°C, the survival of the hybrid and IS5 strains was significantly reduced relative to the HP88 strain. No differences were detected in reproductive potential among the strains. This study demonstrates the potential of using hybridization to genetically improve entomopathogenic nematodes and illustrates the advantages of using marker mutations in this endeavor.

Comparison of Entomopathogenic Nematode Dispersal from Infected Hosts Versus Aqueous Suspension

Dispersal of the entomopathogenic nematodes Heterorhabdidtis bacteriophora Poinar (HP88 strain) and Steinernema carpocapsae (Weiser) (All strain) was measured when nematodes were applied to sand either in Galleria mellonella (L.) cadavers or in aqueous suspension. Dispersal ability was estimated as the percentage of nematodes that migrated through sand or from sand onto an agar surface. Results of overnight assays indicated that the dispersal ability of both species was significantly greater when nematodes were applied in cadavers relative to when they were applied in aqueous suspension. Assays that measured migration onto an agar surface after 1 h also indicated enhanced dispersal of S. carpocapsae when exiting cadavers, but results from H. bacteriophora only weakly supported the trend. The relatively greater movement of nematodes exiting infected hosts was not the result of differences in nematode age or persistence in sand. The enhanced dispersal may have been caused by physiological or behavioral differences between nematodes exiting hosts and those kept in aqueous suspension. Because of the dispersal advantage, application of entomopathogenic nematodes in infected hosts may increase their efficacy in biological control. This study demonstrated a need to further investigate behavior of entomopathogenic nematodes when they exit a host under natural conditions.

Infectivity and Reproduction of Three Heterorhabditid Nematodes (Rhabditida: Heterorhabditidae) in Two Insect Hosts

The infectivity, incubation time, and reproduction of three heterorhabditid nematodes, Heterorhabditis sp. Bacardis and FL2122 strains and H. bacteriophora Poinar HP88 strain were studied in two insect hosts, an apionid weevil, Cylas formicarius (F.), and a pyralid moth, Galleria mellonella (L.). Two of the nematodes, Heterorhabditis sp. Bacardis and FL2122 strains, were of tropical or subtropical origin, whereas the third nematode, H. bacteriophora HP88 strain, was of temperate origin. Infectivity did not differ among nematodes within each host; however, it did differ between hosts for the Bacardis strain. Cylas formicarius was more susceptible to this nematode than G. mellonella. Incubation times also did not differ among nematodes within hosts; however, incubation times were 3.2-4.3 d shorter in C. formicarius than in G. mellonella. Progeny production differed (although not significantly consistent) among nematodes and was highest for Heterorhabditis sp. Bacardis followed by the Heterorhabditis sp. FL2122 and H. bacteriophora HP88 in both hosts. Percentages of infected cadavers that produced progeny were consistently higher for the tropical and subtropical nematodes, Heterorhabditis sp. Bacardis and FL2122, than for the temperate nematode, H. bacteriophora HP88, in both hosts. Patterns of emergence from cadavers were consistent in G. mellonella; most progeny emerged by 23 d after inoculation and emergence lasted for up to 48 d after inoculation. Conversely, emergence patterns varied markedly in C. formicarius. Emergence lasted for up to 29 d after inoculation and peak emergence varied between 12 and 28 d after inoculation. Progeny production in C. formicarius was not related to the biomass of the host cadaver.

Laboratory Efficacy of Selected Species of Entomopathogenic Nematodes Against Blueberry Mealybug, 1995

Abstract Experiments were conducted in plastic Petri dishes (35 mm diam.) filled with coarse sterile sand mixed with distilled water (10% water by weight). A single final instar mealybug on a small piece of fresh blueberry root was buried in the center of each dish. Nematodes were added in a drop of distilled water (50 u.1) applied away from the center of the dish. Different doses of nematodes were applied using the dilution method in which a series of mixtures of nematodes in water was prepared at the appropriate densities for each experiment. In Experiment 1, three species of nematodes, Steinernema carpocapse (All strain), S. glaseri (NC strain) and Heterorhabditis bacteriophora (HP88 strain), were tested at doses of 10, 50, 100, and 500 infective juveniles (ijs) per dish. Mealybug mortality was assessed at 2- and 5-DAT. Each treatment (species/dose/exposure period) was replicated 12 times. Replicates where the mealybug could not be located were omitted from the study. In Experiment 2, we tested S. feltiae (Australia strain) and H. bacteriophora (HbNJ strain) at 50, 100, 500, and 1000 ijs per dish at an exposure period of 5 d, and replicated 24 times per treatment. In both experiments, after treatment application, the dishes were placed in a large food storage box with damp paper towels to maintain a high humidity, and incubated at 25°C. The nematodes for all experiments were reared in Galleria mellonella larvae and used within two weeks of emergence into white traps.

Host Plant Effects on Entomopathogenic Nematodes

We conducted assays to determine the effects of host plant and a plant secondary metabolite, cucurbitacin D, on the mortality of Diabrotica undecimpunctata howardi from infection by entomopathogenic nematodes and on nematode progeny production. Rootworms were produced on corn, peanut, and two squash varieties, one containing cucurbitacin D and the other lacking this secondary metabolite. Rootworms were exposed to the NC, HP88, and Lewiston strains of Heterorhabditis bacteriophora and the All, Mexican, and Agriotos strains of Steinernema carpocapsae. The plant on which the rootworms had fed significantly affected rootworm mortality and nematode progeny production. In general, rootworms which had fed on corn suffered significantly lower mortality than those reared on peanuts or either of the squash varieties. Rootworms that had fed on the squash varieties suffered greatest mortality. Nematode progeny production was highest from rootworms that had fed on corn, lower for peanut, and lowest on squash. Progeny production from rootworms that had fed on bitter squash was lower than from nonbitter squash for all nematode strains tested. Possible effects of cucurbitacins and plant primary metabolites on rootworms and entomopathogenic nematodes are discussed.

Entomopathogenic Nematode Effect on Pickleworm (Lepidoptera: Pyralidae) Under Laboratory and Field Conditions

Laboratory and field tests were performed to assess the potential of entomopathogenic nematodes from the genera Steinernema and Heterorhabditis as biological control agents for the pickleworm, Diaphania nitidalis (Stoll). In the laboratory, there were significant differences in virulence among five nematode species, based on the lack of overlap of95% FL of LC50. S. carpocapsae (Weiser) (Mexican strain) had the lowest LC50 and was ≍2, 4, 30, and 38 times more pathogenic than H. bacteriophora Poinar (HP88 strain), S. feltiae (Filipjev), S. glaseri (Steiner), and S. anomali (Kozodoi), respectively. Nematode infectivity (number of nematodes in the host) was positively correlated with mortality. Larval mortality and penetration rate of infective juveniles into the host were positively correlated to host exposure time for S. carpocapsae (Mexican strain), S. feltiae , and H. bacteriophora . Nematode species that were smaller were more infective and induced mortality more quickly. Nematodes did not affect first instars and pupae to the same extent as older larvae and prepupae; pupae were particularly refractory. S. carpocapsae (All strain) applied to squash plants were able to enter blossoms, where they persisted and infected pickleworms. Nematode applications reduced damage to blossoms and fruit and, when applied weekly at 2.5 billion/ha, protected squash fruit at a level equivalent to the insecticide permethrin.

Laboratory and Field Evaluation of an Entomopathogenic Nematode Genetically Selected for Improved Host-Finding

A strain of Steinernema carpocapsae selectively bred in the laboratory for improved host-finding of scarab larvae did not provide enhanced field efficacy of Japanese beetle larvae, Popillia japonica. Selected (S20) and wildtype (All) strains reduced larval populations by 25-30%, compared with 70% for the chemical insecticide. Similar results were obtained in laboratory exposures conducted in soil-filled pots against the scarab Maladera matrida . The selected S20 strain was, nevertheless, superior to the All and HP88 strains at locating larvae. S20 nematodes, which are known to have enhanced chemosensitivity to carbon dioxide, were observed to aggregate heavily at or near the spiracles. Scarab spiracles are covered with sieve plates and, therefore, are not a portal of nematode entry. Despite selection for greater response to host cues, S20 persisted in nictating, standing on their tails, even when a host was present. The unfavorable field results usually obtained with S. carpocapsae against scarab larvae have been attributed to low powers of host search. Our results indicate that even when larvae are located S. carpocapsae is poorly adapted to cause infection. Genetic improvement cannot he expected to overcome poor adaptation. Future selection efforts with nematodes should begin with species adapted for the target host.

Suppression of Strawberry Root Weevil, Otiorhynchus Ovatus, in Cranberries By Entomopathogenic Nematodes (Nematoda: Steinernematidae and Heterorhabditidae)

Strawberry root weevil (Otiorhynchus ovatus (L.)) larval populations in Massachusetts (U.S.A.) cranberry bogs showed 32-38% mortality following spray application of the entomopathogenic nematodes, Steinernema carpocapsae (A11 strain) or Heterorhabditis bacteriophora (NC-1-strain). A bioassay of larval and pupal O. ovatus with S. carpocapsae resulted in 62% mortality and with H. bacteriophora in 51 % mortality. A post-harvest application demonstrated the limited distribution of the nematodes from the surface to 40 mm depth after 336 h, which may explain the difference between the results from the field and from the bioassay. A following trial with increased spray pressure reduced the 0. ovatus population from 26.7 to 0.6 live larvae per sample (with S. carpocapsae) and from 16.2 to 1.8 live larvae per sample (with H. bacteriophora, HP88 strain) after 240 h. In this trial, bioassay of 0. ovatus resulted in 74.0% mortality with S. carpocapsae and 68.8% mortality with H. bacteriophora.

Field Efficacy and Persistence of Entomopathogenic Nematodes (Rhabditida: Steinernematidae, Heterorhabditidae) for Control of Sweetpotato Weevil (Coleoptera: Apionidae) in Southern Florida

The entomopathogenic nematodes Steinernema carpocapsae (Weiser) (All, S17, and S20 strains), S. feltiae (Filipjev) (= S. bibionis) (N27 strain), Heterorhabditis bacteriophora (Poinar) (HP88 strain), and Heterorhabditis sp. (Bacardis strain) were evaluated as biological control agents of the sweetpotato weevil, Cylas formicarius (F.), during two consecutive growing seasons in southern Florida. Two strains, S17 and S20, were genetically selected over 17 and 20 generations, respectively, for enhanced finding of the host scarab Popillia japonica Newman. Steinernematid nematodes were applied as aqueous suspensions. The heterorhabditid nematodes, tested only in the second year, were applied using cadavers of greater wax moth, Galleria mellonella (L.), infected with these nematodes. Abundance and damage of weevils differed among nematode treatments. In the first experiment, S. carpocapsae All and S17 were most efficacious at reducing weevil damage and produced the highest percentages of marketable roots. In the second experiment, the heterorhabditid nematode, HP88, was most efficacious at reducing weevil damage to storage roots. All of the steinernematids, except S20 applied at a high rate (7.9 billion infective juveniles per ha), produced comparable percentages of marketable roots but were less efficacious than HP88. In the first experiment, S. carpocapsae All and S17 persisted poorly, whereas S. feltiae N27 persisted for >160 d after application. In the second experiment, most nematodes were recovered at moderate levels for >120 d after application; however, only Heterorhabditis sp. Bacardis was consistently recovered at high levels for >230 d after application.

Infectivity of Five Entomopathogenic Nematodes to the Sweetpotato Weevil, Cylas formicarius (F.), (Coleoptera: Apionidae) in Three Experimental Arenas

The infectivity of five nematodes [ Steinernema carpocapsae (Weiser) (= Neoaplectana carpocapsae, Steinernema feltiae) All and Mexican strains, Steinernema feltiae (Filipjev) (= Steinernema bibionis) N-27 strain, Heterorhabditis bacteriophora Poinar (= Heterorhabditis heliothidis) HP88 strain; and Heterorhabditis sp. FL2122 strain (an undescribed nematode isolated in Florida)] were compared in three experimental arenas. Infectivity was determined by the number of infective juveniles established in Cylas formicarius (F.) larvae. The experimental arenas consisted of a standard petri plate/filter paper arena and a 30-ml vial filled with coarse construction sand or a Krome loam soil. Nematodes and individual larvae were placed at opposite ends in the vial. Larvae were replaced every 2 days for 16 days in all test arenas. Heterorhabditis sp. FL2122 was more effective at establishing in larvae than all other nematodes in all three experimental arenas. There were significant differences in nematode establishment among experimental arenas for each nematode tested. Steinernema carpocapsae strains were favored in the petri plate arenas while Heterorhabditis spp./strains were favored in the sand arena. Nematode establishment increased with time for the first 4 to 8 days and then leveled off for the remaining test period for most nematode-bioassay combinations.

Within-Root Mortality of Cylas formicarius (Coleoptera: Apionidae) by Entomopathogenic Nematodes

Within-root mortality of sweetpotato weevil, Cylas formicarius (F.), by six strains of entomopathogenic nematodes in the families Steinernematidae and Heterorhabditidae ( Steinernema carpocapsae \[Weiser\] \[= Neoaplectana carpocapsae, Steinemema Feltiae \] All and Mexican strains; Steinernema feltiae \[Filipjev\] \[= Steinemema bibionis \] N-27 strain; Steinernema glaseri [Steiner]; Heterorhabditis bacteriophora Poinar [= Heterorhabditis heliothidis] HP88 strain; and Heterorhabditis sp. FL2122 strain [an un-described nematode isolated in Florida]) was tested in several buried-root bioassays. The ability of nematodes to locate and kill weevils, and the location within the root where infection occurred, were measured. In addition, mortality of the weevils in roots that were artificially infested in the laboratory was compared with mortality in naturally infested roots from the field using two concentrations of one nematode ( s. carpocapsae Mexican strain). In general, the heterorhabditid nematodes caused higher levels of mortality within the root than the steinernematids. Heterorhabditis sp. FL2122 strain killed the highest proportion of weevils in the shortest period of time. Similar differences among nematodes were seen in the inner portion (½ radius) of the storage roots, as well as ill the outer portion. Although weevil mortality in the artificially infested roots was greater than in the naturally infested roots, the trends in mortality were similar; we observed increased mortality in the nematode treatments compared with the control and no difference in mortality between the two nematode concentrations.

Efficacy of Entomopathogenic Nematode Strains Against Popillia Japonica (Coleoptera: Scarabaeidae) Larvae

Control of Japanese beetle ( Popillia Japonica Newman) larvae by Heterorhabditis Bacteriophora Poinar (HP88 strain and a New Jersey strain, NJ-2) and Steinemema glaseri Steiner (NC strain and a New Jersey strain, NJ-43) showed that all strains reduced larval populations to a level comparable with that achieved by use of bendiocarb. Nematode strains and species did not differ significantly in mean level of population reductions ( H. bacteriophora HP88 and NJ-2, 51.0 and 71.6%; S. glaseri NC and NJ-43, 50.4 and 70.1%, respectively). However, variation in the level of population reduction provided by NJ-43 was less than that by the NC strain. After a 3-wk test period, nematode persistence and downward migration in the field did not differ among species and strains. In a laboratory bioassay, New Jersey strains provided higher levels of larval mortality compared with strains cultured in the laboratory for at least a decade. A new method used to count viable bacteria retained by individual infective juveniles showed that NJ-43 not only retained more bacteria than the NC strain (19.5 ± 0.2 compared with 4.9 ± 0.06 bacteria per infective juvenile) but also that the proportion of nematodes retaining bacteria was higher (77% compared with 55%). Bacterial retention by infective juveniles did not differ significantly between H. bacteriophora strains.

Entomopathogenic Nematodes for Control of Root Weevils of Citrus

The entomopathogenic nematodes, Steinernema carpocapsae (All strain), Heterorhabditis bacteriophora (HP-88 strain), H. bacteriophora (Florida strain), applied to the soil of a citrus grove near Lake Jem, Florida in March 1989, significantly reduced adult emergence of the root weevil, Diaprepes abbreviatus (L.). The total number of weevils captured in 160 traps from April 1989 through May 1990 was 833. Weevil emergence was reduced 70% compared with the check in May, June, and September (1989) and March and April 1990. There was no difference between nematode treatments. Efficacy trials conducted in a grove in Fort Pierce, Florida, for control of the citrus root weevil, Pachnaeus opalus and P. litus, gave similar results. A study to determine seasonal variation of a native heterorhabditid population in a grove adjacent to the Lake Jem grove was inconclusive.

Effects of Entomopathogenic Nematode Species, Rate, Soil Moisture, and Bacteria on Control of Japanese Beetle (Coleoptera: Scarabaeidae) Larvae in the Laboratory

Several strains or species of entomopathogenic nematodes, Steinernema Carpocapsae Weiser (All and Mexican strains), S. feltiae (=bibionis) (Filipjev) (Biosys #27), S. glaseri (Steiner) (Biosys #2), and Heterorhabditis bacteriophora (= heliothidis) Poinar (HP88 and Cl strains) were tested in the laboratory for their effect on larvae of Japanese beetle, Popillia japonica Newman. Mean larval mortality ranged from 17.8 to 99.4% depending upon nematode strain and rate of application. S. glaseri caused a greater percentage of mortality of P. japonica larvae than any other species or strain of nematode tested. No interactions between nematode strains, application rates, and soil moisture were significant. Larval mortality generally increased with increased nematode rates. In separate experiments, nematode symbiotic bacteria, Xenorhabdus luminescens Thomas & Poinar, X. nematophilus (Poinar & Thomas), and X. poinarii (Akhurst) were injected into Galleria mellonella (L.) and P. japonica larvae to determine pathogenicity. X. luminescens was the most pathogenic bacterium to both species, followed closely by X. nematophilus. X. poinarii demonstrated low pathogenicity to both insect species.

Movement and postinfection emergence of entomopathogenic nematodes from sweetpotato weevil, Cylas formicarius (F.) (Coleoptera: Apionidae)

Abstract Emergence and movement of five entomopathogenic nematode species [ Steinernema carpocapsae (Weiser) All strain; S. feltiae (Filipjev) (= S. bibionis ) N-27 strain; S. glaseni (Steiner); Heterorhabditis bacteriophora Poinar HP88 strain; Heterorhabditis sp. FL2122 strain (an undescribed nematode isolated in Florida)] from Sweetpotato weevil cadavers, Cylas formicarius (F.), within sweet potato, Ipomoea batatas (L.) Lam., storage roots, was measured using a Galleria mellonella (L.) baiting technique. Weevil-infested storage roots were exposed to the nematodes and then buried in sand or soil in the laboratory and in the field. In both sand and soil environments (laboratory and field), all nematode species tested were recovered, with the heterorhabditid species causing more mortality of the bait insect than the steinernematid species. All nematode species were capable of moving horizontally at least 15 cm from the weevil cadavers within the swollen root in a soil environment in the laboratory. The heterorhabditid nematodes and to a lesser extent, S. feltiae and S. glaseri , were capable of locating and infecting weevils within swollen roots placed 15 cm away from the swollen root from which they exited. Steinernema carpocapsae was not capable of infecting weevils within these roots. All nematode species mentioned above and S. carpocapsae Mexican strain were applied to the field as a point-source inoculation and were recovered 60 cm horizontally from the point of application with the heterorhabditid nematodes and S. glaseri causing the most mortality of the bait insect.

Comparison of Ten Entomopathogenic Nematodes for Control of Sweetpotato Weevil (Coleoptera: Apionidae)

Ten entomopathogenic nematode species or strains in the families Stein-ernematidae and Heterorhabditidae-Steinernema carpocapsae (Weiser), Agriotos, All, Breton, Italian, and Mexican strains; Steinernema feltiae (Filipjev), N27 strain; Steinernema intermedia (Poinar); Heterorhabditis bacteriophora, Poinar, HP88, and North Carolina strains; and an unidentified Heterorhabditis sp. FL2122 strain-were compared in the laboratory against the sweetpotato weevil, Cylas formicarius (F.). Although all nematodes tested could kill sweetpotato weevils, there were differences among the nematodes. Larval LC50S were low for most nematodes tested (< 10 infective juveniles per insect). The heterorhabditid nematodes included the most virulent nematode (unidentified Heterorhabditis sp. FL2122 strain), and the least virulent nematode (H. bacteriophora North Carolina strain). Heterorhabditid nematodes were more pathogenic to pupae than were steinemematid nematodes. Weevil adults were the least susceptible stage to nematode infection. With the exception of S. carpocapsae All strain, adult mortality was < 6% for all nematodes. Adult mortality by All strain ranged from 25 to 60% depending on the nematode concentration applied. Male weevils accounted for 96-100% of the adult mortality by All strain. Larval mortality from nematode infection increased significantly over a 4-d period for all nematodes with the exception of S. feltiae, which caused high mortality within 24 h. Heterorhabditid nematodes produced Significantly more infective juveniles per cadaver than did steinernematid nematodes. The importance of these data for selecting suitable nematodes for biological control of the sweetpotato weevil is discllssed.

Persistence of Control of Japanese Beetle (Coleoptera: Scarabaeidae) Larvae with Steinernematid and Heterorhabditid Nematodes

Field tests were conducted in 1986 and 1987 to evaluate control of Japanese beetle larvae, Popillia japonica Newman, in turfgrass plots by heterorhabditid and steinemematid nematodes. Heterorhabditis bacteriophora Poinar (NC strain) reduced populations a maximum of 60%, 34 d after a fall 1986 treatment. Control increased to 96% before pupation the following spring, and was 93-99% of the next larval generation. Application of Steinemema (=Neoaplectana) carpocapsae Weiser (All strain) provided a maximum of 51% control after 34 d, 90% the next spring (290 d after treatment), and 0% after 386 d. A spring 1987 application of H. bacteriophora resulted in 68% control 28 d after treatment, and up to 67% of the following generation of] apanese beetle larvae in the fall (138 dafter treatment). H. bacteriophora (HP88 strain) gave 100% control after 28 d in the spring of 1987, and 93-97% control of the next generation of larvae. No adverse effects on nontarget organisms (mites or collembola) were observed 28 d after treatments with any of the nematodes. Our data show that nematodes reproduce in Japanese beetle larvae, survive in the field in turfgrass, and have an influence on target hosts for a longer period oftime than previously demonstrated.

Comparison of single and multiple releases of Heterorhabditis bacteriophora Poinar (Nematoda: Heterorhabditidae) for control of Cylas formicarius (Fabricius) (Coleoptera: Apionidae)

Abstract Single and multiple releases of the entomopathogenic nematode, Heterorhabditis bacteriophora Poinar (= H. heliothidis Khan, Brooks, and Hirschmann) (HP88 strain), were evaluated for controlling populations and damage of the sweetpotato weevil, Cylas formicarius (Fabricius), during two consecutive growing seasons in southern Florida. Sweet potato, Ipomoea batatas (L.) Lam., plants were treated with one, two, or three applications of H. bacteriophora in a Krome very gravelly loam soil. Weevil population reduction and damage in nematode-treated sweet potato plots were compared with that in plots treated with monthly applications of chemical insecticides and in nontreated plots. Persistence of nematodes in soil was assessed at various times after release by baiting soil samples with greater wax moth larvae, Galleria mellonella (L.). Applications of H. bacteriophora did not consistently reduce weevil abundance, but did consistently reduce damage to sweet potato storage roots compared with nontreated plants. Weevil densities and damage did not differ between plants treated with one, two, or three applications of H. bacteriophora , suggesting that a single, early season release of this nematode was adequate for managing this weevil. Weevil damage on plants treated with chemical insecticides was intermediate to that on nematodetreated and nontreated plants. H. bacteriophora persisted in soil for over 130 and 250 days after application in the first and second experiment, respectively.