RESEARCHES ON STEINERNEMA SCAPTERISCI

Dispersal of Steinernema scapterisci (Rhabditida: Steinernematidae) after Inoculative Applications for Mole Cricket (Orthoptera: Gryllotalpidae) Control in Pastures

ABSTRACT: The passive dispersal of Steinernema scapterisci Nguyen & Smart by its hosts was monitored and quantified after inoculative releases consisting of 1-ha applications in each of six pasture sites in Florida. Pitfall trap catches of Scapteriscus spp. mole crickets were used to determine levels of infection, dispersal of the nematode from release areas, and effects on mole cricket abundance for 2 years after the releases. The nematode was established at five of the sites and dispersed at least 150 m from release areas at three of them. Mean maximum cumulative distance dispersed (60 m) and cumulative area occupied (4.2 ha) by the nematode occurred within 21 months after application. The relationship between mean cumulative distance dispersed and time is described most accurately by the polynomial equation Y = 0.453 + 0.030X2 -0.0002X3 where Y = mean cumulative distance dispersed (m) and X = number of weeks after treatment. Mean infection levels for mole crickets collected from within the treated area, on the edge of the treated area, and 50 and I50 m from the treated area were 14.6, 12.1, 5.0, and 2.8%, respectively. Twenty-four-hour trap catches, mole cricket tunnel estimates, and soap-flushes of mole crickets failed to reveal consistent effects of the nematode on mole cricket abundance. However, our study has shown that an entomopathogenic nematode species, in particular, S. scapterisci, can be used as a classical biological control agent. Inoculative release of this nematode is a viable alternative to inundative release for mole cricket suppression.

Establishment and Persistence of Steinernema scapterisci (Rhabditida: Steinernematidae) in Field Populations of Scapteriscus spp. Mole Crickets (Orthoptera: Gryllotalpidae)l

ABSTRACT: The first successful inoculative releases of an entomopathogenic: nematode, Steinernema scapterisci Nguyen and Smart, for the control of exotic pests, Scapteriscus spp. mole crickets, were made at three pasture sites in Alachua County, Florida in 1985. Based on the evaluation of field-collected crickets, the nematode was established at all sites and persisted for over 5 years. Mean yearly percentage of infected crickets ranged from 0 to 21.4% for individual release sites. Mean adult infection level for all years combined, 10.9%, was significantly greater than that for nymphs (2.5%) and infection levels for Scapteriscus borellii GiglioTos, 12.7%, was significantly greater than that for Scapteriscus vicinus Scudder (4.5%) for all years combined. Although 24 h trap catch results indicate mole cricket populations were significantly reduced, the nematode's effect on pest abundance could not be adequately assessed because of the variation in trap catch results and inadequate knowledge about the relationship between trap catch and the mole cricket field populations being sampled. Despite inadequacies in estimating pest abundance, the results indicate S. scapterisci has potential as a biological control agent for pest mole crickets in the genus Scapteriscus.

Inoculative Release of Steinernema scapterisci (Rhabditida: Steinemematidae) To Suppress Pest Mole Crickets (Orthoptera: Gryllotalpidae) on Golf Courses

ABSTRACT: Single inoculative applications of Steinernema scaptelisci were made on golf courses in north central (Alachua County) and southeastern (Broward County) Florida. Nematode-infected Scapteriscus spp. mole crickets were collected from eight of nine treated plots and from five of six treated plots in Alachua and Broward counties, respectively. However, infected individuals were collected with regularity from only two courses in Alachua County where level of infection was greatest during the spring (March-June). Weekly infection levels for weeks 1-12 after treatment ranged from 0-100%. Infection of Scapteriscus spp. adults from treated plots in Alachua County, 25.2%, was significantly greater than that for nymphs, 1.2%; and infection of Scapteriscus borellii, 25.0%, was significantly greater than that of S. vicinus, 11.0%. Nematode-infected mole crickets were collected from four control plots in Alachua County and from one in Broward County during the 2nd yr after treatment. Significantly fewer mole crickets were collected in 24-h trap catches the 2nd yr after treatment on all treated plots combined and control plots combined in both counties. Mean trap catch was reduced 68, 62, and 41% the 2nd yr on treated plots where the nematode persisted; on control plots where infected crickets were collected; and on control plots where the nematode was not detected, respectively. Damage ratings and number of mole crickets soap-flushed from treated plots were significantly reduced the 2nd yr after treatment. Results indicate S. scapterisci can serve as an inoculative biological control agent for Scapteriscus spp. mole crickets on golf courses and as a biopesticide for relatively rapid suppression of pest populations.

ABSTRACT: Bacteria from Steinernerna scapterisci were isolated and cultured in the laboratory either in vivo or in vitro and collected from two field locations. The bacteria were identified by gas-liquid chromatography of their fatty acid methyl esters using the MIDI Microbial Identification System. The bacteria clustered into three groups. All but one strain in one group were identified as Ochrobactrum anthropi, the odd strain was identified as Paracoccus denitrificans. A second group was identified as Xanthomonas maltophilia. A third group, although identified by the MIDI system as different genera and species, were shown by dendrogram cluster analysis techniques to be in the same genus and perhaps divided into four species. We consider all members of the third group to be in the genus Xenorhabdus.

Development, Reproduction, and Pathogenicity of Steinemema scapterisci in Monoxenic Culture with Different Species of Bacteria

ABSTRACT: Associations between steinernematid nematodes and their symbiotic bacteria are of fundamental importance. The reported bacterial symbionts of all species of Steinernema are in the genus Xenorhabdus. This paper reports on the development, reproduction, and pathogenicity of infective juveniles of Steinernema scapterisci produced on bacteria other than Xenorhabdus spp. The nematode developed and reproduced on a number of bacterial species, including Escherichia coli, Ochrobactrum anthropi, Paracoccus denitrificans, Pseudomonas aureofaciens, Pseudomonas fluorescens Biovar B, Xanthomonas maltophilia, Xenorhabdus nematophilus, and Xenorhabdus spp. Although adult development occurred on all bacterial species, progeny production after 14 days was significantly greater on X. nematophilus and P. fluorescens Biovar B than on the other bacterial species. Infective juveniles which were produced on 0. anthropi, P. denitrificans, P. aureofaciens, and X. nematophilus caused equal mortality to the southern mole cricket, Scapteriscus borellii. Since Xenorhabdus spp. is reported to change from a primary phase to a secondary phase with reproduction being considerably less on the secondary phase, and since the nematodes were equally pathogenic when produced on other bacteria, it may be more efficient to produce the nematode on bacteria other than Xenorhabdus rather than contend with phase variation.