Dawn H Gouge

Abstract:

Diapausing larvae of Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae), were exposed to entomopathogenic nematodes (Nematoda: Steinernematidae; Heterorhabditidae) at a dosage of 100 or 200 infective juveniles (IJ) per larva. No significant differences between infection of Steinernema riobrave (strain 355) Cabanillas, Poinar and Raulston, and Heterorhabditis bacteriophora (strain Cruiser) (Poinar) were observed after either 6-d or 9-d of incubation. No significant difference in infection levels occurred due to increasing dose. Greatest insect mortality occurred due to parasitism by S. riobrave (355). In a second assay, diapausing larvae of P. gossypiella were exposed to S. riobrave (355), Steinernema carpocapsae (strain Kapow) (Weiser), H. bacteriophora (strain Lawn Patrol), or H. bacteriophora (Cruiser) at dosages of 50, 100,200, or 400 IJs per larva. S. carpocapsae and H. bacteriophora (Cruiser) infected larvae at significantly higher rates compared with H. bacteriophora (Lawn Patrol) and S. riobrave. A significant difference in infection levels occurred due to nematode dose. In a third assay cotton bolls infested with diapausing P, gossypiella were exposed to S, riobrave (355), or H. bacteriophora (Cruiser). Boxes were prepared with bolls buried 5 cm below the soil surface or bolls laid on the soil surface. Boxes also were incubated at constant temperature or exposed to ambient seasonal temperatures and light. H. bacteriophora (Cruiser) infected larvae at significantly higher rates compared with S. riobrave (355). Significant differences in infection levels occurred due to the location of the boll placement and the incubation temperature.

PMID: 16334314;Abstract:

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°C. S. glaseri, H. marelatus, and H. bacteriophora caused significant mortality at 22°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°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. © 2005 Entomological Society of America.

Abstract:

Experiments were conducted to determine the effect of temperature on entomopathogenic nematode infection of an insect host. Late instars of Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae), Heliothis virescens (F.) (Lepidoptera: Noctuidae), Trichoplusia ni (Hubner) (Lepidoptera: Noctuidae), and Spodoptera exigua (Hubner) (Lepidoptera: Noctuidae) were incubated at 10 temperatures ranging between 9.9 and 40°C, and exposed to 150 infective juvenile entomopathogenic nematodes (Nematoda: Steinernematidae; Heterorhabditidae) per larva. The number of infecting Steinernema riobrave Cabanillas, Poinar and Raulston, S. carpocapsae (Weiser) (Kapow) and Heterorhabditis bacteriophora (Poinar) (Cruiser), nematodes was recorded. Temperature, nematode species, and target insect all significantly affected the number of infective juvenile nematodes invading host insects. The temperature supporting the highest levels of nematode infection varied depending on insect host species. Larvae of P. gossypiella were then incubated at the same range of temperatures, and exposed to 2 dose rates (100 and 200 infective juveniles per larva) of S. riobrave, S. carpocapsae (Guardian), H. bacteriophora (Cruiser), or H. bacteriophora (Lawn Patrol). Increasing nematode dosage had no effect on the temperature at which nematode infection of P. gossypiella was highest. Doubling the nematode dose rate did not result in a significant increase in the number of infective juveniles infecting larvae for the nematode species tested with the exception of S. riobrave. The optimum temperature for the control of insect targets by a nematode will vary among target species. Assuming existing nematode temperature optima and applying the same conditions to untested insect species may not result in maximum biocontrol efficacy.