BIOLOGY

ABSTRACT: The life cycle of Steinernema scapterisci Nguyen and Smart, 1990 consists of an egg stage, four juvenile stages, and an adult stage (male and female). The cycle from IJ (third stage infective juveniles) to IJ may proceed by one of two routes. If the nutrient supply is sufficient and the population is not overcrowded, the IJ develop to adult males and females of the first generation. Most eggs from these adult females hatch and the juveniles develop through each life stage to become adult males and females of the second generation. Eggs produced by these females develop to IJ. This cycle takes 8-10 days (long cycle) at 24 C. If the nutrient supply is insufficient or if overcrowded, the IJ develop to adult males and females of the first generation, and eggs produced by the females develop directly to IJ. This cycle takes 6-7 days (short cycle). The nematode is less tolerant of lower temperatures and more tolerant of higher temperatures than are other species of the genus. The sex ratio is influenced by temperature. At 15 and 24 C, females constituted 54% and 60% of the population, respectively, but at 30 C females constituted 47% of the population.

ABSTRACT: 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.

Preliminary Studies on Survival of Steinernema scapterisci in Soil

ABSTRACT: The nematode Steinernema scapterisci was brought to Florida from Uruguay as a possible biological control agent of pest mole crickets. Experiments have shown that it provides effective control, but little is known about survival of the nematode in Florida's environment. Since survival is of utmost importance if the nematode is to recycle and continue to control mole crickets, the experiments reported here were conducted to acquire some information on survival of the nematode during summer and winter. All experiments were conducted by placing infective stage juveniles of the nematodes in soil in containers which were either tightly sealed or sealed with a fine mesh cloth to prevent the nematodes from escaping. Containers were removed each week up to 14 wk and the surviving juveniles recovered from the soil. Survival of the juveniles declined gradually over time, but 28% of those applied were recovered after 8 wk when buried in tightly sealed containers of sterilized soil. When buried in cloth-sealed containers of sterilized soil, survival declined rapidly at the second week, but only gradually thereafter, with 16% recovered after 10 wk. At the end of each experiment, the juveniles recovered were infective. When infective juveniles were buried in tightly sealed containers of unsterilized soil, 29% survived at week 6 but survival declined rapidly thereafter with only 0.4% of the original number recovered at week 14. Those recovered at weeks 6 through 8 were infective; very few were recovered at weeks 9 through 14 and they were not tested for infectivity. Since in all tests 15 to 35 % of the juveniles survived for 6 wk and were infective, we believe it is highly probable that the nematode will survive long enough when applied to the soil to encounter and infect a host.

Vertical dispersal of Steinernema scapterisci

ABSTRACT: When infective juveniles of Steinernema scapterisci Nguyen & Smart were released on the soil surface in the field and in the laboratory, some of them moved downward through the soil at least 10 cm in 5 days and infected and killed mole crickets. When released 2 cm below the soil surface, most of the juveniles moved into the upper 2 cm layer of soil, but some moved downward 10cm. When placed at the center of a 16-cm soil column, infective juveniles moved in both difections with three times more moving downward than upward. Infective juveniles were more efficient in killing mole crickets in the field than in the laboratory.

THE ROLE OF SOME ABIOTIC SOIL FACTORS IN THE SURVIVAL AND MOTILITY OF STEINERNEMA SCAPTERISCI

Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science. December 1990

This study examines some effects of selected soil factors on the insect parasitic nematode Steinernema scapterisci. The main objectives of the study were to examine the influence of soil texture on the motility of juveniles of S. scapterisci and to assess the effects of soil moisture on their survival.

The dispersal of S. scapterisci was evaluated in a sand (98% sand, 0% silt, 2% clay), a loamy sand (89.5% sand, 1.5% silt, 9% clay), a sandy clay loam (77% sand, 1% silt, 22% clay) and an organic soil. Motility was assessed in lab assays which used an insect host, Acheta domesticus (the house cricket), as an indicator of nematode dispersal.

The ability of S. scapterisci to reach and infect hosts decreased as the clay content of the soil increased from 2 to 22%. The percent of available hosts infected was significantly lower for the sandy clay loam soil than for the other soils tested. Dispersal of infective juveniles was not significantly affected by an organic soil.

The influence of soil moisture on juveniles of S. scapterisci was evaluated for moistures ranging from above field capacity to below wilting point in two loamy sand soils and a sandy soil. In sand, survival was compared to a related insect parasite, S. carpocapsae (All strain). Juveniles of S. scapterisci survived up to 13 weeks at wilting point (15 bars moisture tension) in all soils tested. At moistures below wilting point, juveniles survived longer in a sandy loam (87.5% sand, 9% silt, 3.5% clay) than in a sand (98% sand, 0% silt, 2% clay). Nematode survival did not decrease significantly over the period of the experiments (8 or 13 weeks) for most of the soil moistures tested. All juveniles recovered from the soils infected house crickets in petri dish tests.

In the sand soil, significantly more S. scapterisci survived longer in soil moisture levels at wilting point and below than did S. carpocapsae (All strain). Fewer than 2% of the juveniles of S. carpocapsae were recovered after 5 weeks at moisture levels below wilting point. Recovery for juveniles of S. scapterisci, however, was still above 57% at 5 weeks and showed no significant decrease over an 8 week period at the same moisture level in this soil.