Influence of production and bioassay methods on infectivity of two ambush foragers (Nematoda: steinernematidae)

The influence of production and bioassay methods on infectivity of two ambush foragers, Steinernema carpocapsae and Steinernema scapterisci, was evaluated. Both species were mass-produced in vitro in liquid culture and in vivo using live insects: S. carpocapsae in last instar wax moth Galleria mellonella larvae and S. scapterisci in adult house crickets Acheta domesticus. Infectivity was assessed at 28 degreesC against last-instar G. mellonella larvae using a filter-paper bioassay and a newly developed "sand-well" bioassay. The infectivity of S. carpocapsae was not influenced by the method of production or bioassay, whereas the infectivity of S. scapterisci was influenced by both factors. Both in vivo and in vitro produced S. carpocapsae caused >60% larval mortality at one nematode per larva (1:1) in the filter-paper bioassay, but S. scapterisci elicited less than 10% mortality. At 50 nematodes per larva, in vitro S. scapterisci caused 41.7% mean larval mortality in the filter-paper bioassay, whereas in vivo S. scapterisci elicited only 28.5% mortality. The replacement of filter paper with a 2.5-mm-deep layer of sand (termed sand well) resulted in 2.5-fold increase in infectivity of S. scapterisci. In the new sand-well procedure, 15 S. scapterisci per larva (15:1) caused an overall mean larval mortality of 47.5% and the pattern of mortality showed a normal distribution. The infectivity of S. carpocapsae was not different in the 1:1 filter paper or 1:1 sand-well bioassay. These results demonstrate that nematode infectivity could be strongly influenced by both the production and bioassay methods, and there are no universal assays even when nematodes have similar foraging strategies. Copyright 1999 Academic Press.

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.

Susceptibility and behavioral response of red imported fire ant (Hymenoptera: Formicidae) to selected entomogenous nematodes (Rhabditida: Steinernematidae & Heterorhabditidae).

Pathogenicity of infective juveniles of selected Steinernema spp. and Heterorhabditis spp. toward developing and reproductive stages of the red imported fire ant, Solenopsis invicta Buren, was tested under laboratory conditions. At 10(3)-10(5) infective juveniles per Petri dish, mortality of reproductive larvae, pupae, and alates ranged from 28 to 100% at higher doses after 96 h at 23-25 degrees C. Steinernema carpocapsae All was the most consistent species tested; this nematode caused mortality of fire ant larvae, pupae, and alates of 82-94, 64-96, and 38-99%, respectively. Although not susceptible to nematode infection, worker ants vigorously preened nematodes from brood, alates, and themselves. In a field study, S. carpocapsae (5 x 10(6) and 2 x 10(6) drench, 2 x 10(6) infective juvenile infection) was applied to active fire ant mounds in 3.8-liter suspensions. Hydramethylnon (75 ml), a water drench, a water injection, and untreated fire ant mounds were marked and treated. Overall activity in mounds treated with nematodes of hydramethylnon ranged from 40 to 48%. Satellite mound activity accounted for 32-44% of overall activity in mounds treated with nematodes 2 wk after treatment. However, 6 wk after treatment, activity in mounds treated with hydramethylnon was 44%; activity of mounds treated with nematodes ranged from 52 to 80%. Satellite mound activity accounted for 0-24% of overall activity. Whereas a soil drench of S. carpocapsae showed potential as a control method for the red imported fire ant, colony relocation after nematode treatment could limit overall efficacy unless application techniques are developed to overcome or take advantage of the movement.

Field Evaluation of Steinernema feltiae Against the Web-spinning Larch Sawfly Cephalcia lariciphila.

Field trials were conducted in Rheola Forest, Wales, Great Britain, to determine the effectiveness of Steinernema feltiae UK strain in controlling the web-spinning larch sawfly Cephalcia lariciphila. Foliar sprays at the rate of 5,000-20,000 nematodes/100 cm branch resulted in 3.4-29.4% infection of sawfly larvae. Soil application of 200 nematodes/cm(2) resulted in 61% infection of sawfly prepupae and 17.3% of pupae. Prepupal infection ranged from 4.8 to 14.7% 1 year after nematode application. Soil applications of this nematode show that it has potential for biological control of sawfly prepupae.

Soil Applications of Steinernematid and Heterorhabditid Nematodes for Control of Colorado Potato Beetles, Leptinotarsa decemlineata (Say).

Three strains of Steinernema feltiae Filipjev (All, Mexican, and Breton strains) and one of Heterorhabditis heliothidis (Khan, Brooks, and Hirschmann) were evaluated for their potential to control Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say), larvae and pupae in the soil. In laboratory studies, H. heliothidis and S. feltiae (Mexican strain) produced the highest mortality (6 days posttreatment) of CPB when applied to the surface of a soil column containing mature CPB larvae 5 cm below. Mortality ranged from 80 to 90% at rates of 79-158 nematodes/cm(2). Similar results were seen in a field microplot study with all four nematodes; S. feltiae (Mexican strain) and H. heliothidis were most effective. Adult CPB emergence was reduced 86.5-100% after application of 31-93 H. heliothidis/cm(2) and 88.4-100% with 93-155 S. feltiae (Mexican strain)/cm(2). The All strain of S. feltiae was moderately effective (ca. 80% reduction at 93-155 nematodes/cm(2)), while the Breton strain was ineffective (< 40% reduction at 155 nematodes/cm(2)). In small plots of potatoes enclosed in field cages, application of H. heliothidis and S. feltiae (Mexican strain) at rates of 93-155 nematodes/cm(2) before larval CPB burial in the soil resulted in 66-77% reduction in adult CPB emergence. Soil applications of these nematodes show potential for biological control of CPB.

Survival and Movement of Insect Parasitic Nematodes in Poultry Manure and Their Infectivity Against Musca domestica.

Survival, infectivity, and movement of three insect parasitic nematodes (Steinernema feltiae All strain, S. bibionis SN strain, and Heterorhabditis heliothidis NC strain) in poultry manure were tested under laboratory conditions. The majority (70-100%) of the nematodes died within 18 hours after exposure to the manure. Nematodes exposed to manure slurry for 6 hours killed at least 95% of the house fly larvae, Musca domestica, but nematodes exposed for 12 hours achieved less than 40% larval mortality. The majority (90-97%) of the three nematode species applied to the manure remained on the surface. Poor survival and limited movement of nematodes in poultry manure appear to make them unlikely candidates for biocontrol of filth flies in this habitat.

Effect of Soil Texture on the Distribution and Infectivity of Neoaplectana carpocapsae (Nematoda: Steinernematidae).

The vertical migration of N. carpocapsae infective juveniles applied to the soil surface or introduced 14 cm below the soil surface was studied in four different soil types (pure silica sand, coarse sandy loam, silty clay loam, and clay). The percentage of juveniles able to migrate and infect wax moth pupae placed in the soil decreased as the percentage of clay and silt increased. Most nematodes placed on the soil surface remained within 2 cm of the surface, but some penetrated to a depth of 10 cm in pure silica sand and coarse sandy loam to infect pupae. Some pupae at the same depth were also infected with nematodes in silty clay loam soil. In pure silica sand and coarse sandy loam, nematodes introduced 14 cm below the soil surface were able to infect wax moth pupae located between 4 and 24 cm. Movement was least in clay soil and limited in silty clay loam. Nematodes showed a tendency to disperse upwards from the point of application. In all cases the number of migrating nematodes was greatest when wax moth pupae were present.

Effect of Soil Texture on the Distribution and Infectivity of Neoaplectana glaseri (Nematoda: Steinernematidae).

The vertical migration of infective juveniles of Neoaplectana glaseri applied to the soil surface or introduced 16 cm below the soil surface was studied in pure silica sand, coarse sandy loam, silty clay loam, and clay. The number of juveniles that migrated and infected wax moth pupae placed in the soil decreased as the proportion of clay and silt increased. The majority of nematodes moved downwards 2-6 cm from the surface, but some penetrated to a depth of 14 cm in pure silica sand and coarse sandy loam. In pure silica sand and coarse sandy loam, nematodes introduced 16 cm below the soil surface were able to infect wax moth pupae located at depths of 0-4 cm and 28-32 cm. Nematodes showed a greater tendency to disperse downwards from the point of application. Movement of the nematode was least in clay soil and limited in silty clay loam soil. The number of migrating nematodes was greatest when wax moth pupae were present.