Interactions between predators and insect-parasitic nematodes in soil
In an agricultural setting the soil community plays a critical role in decomposition, nutrient cycling and the control of pathogens and pests of crops. Conservation and augmentation of soil-dwelling predators and pathogens may enhance the control of agricultural pests. The purpose of this research is to examine the response of soil fauna to an applied logical control agent; insect-parasitic nematodes.
Insect-parasitic nematodes in the families Steinernematidae and Heterorhabditidae occur naturally in the soil and are also applied inundatively, like a pesticide, at the commercial rate of 2.5 billion/hectare. In field applications, recovery of nematodes directly following application may yield less than 50%. This has generally been attributed to abiotic factors.
Biotic factors, however, may also impact applied or augmented nematode populations.
The objectives of this research were to:
1) Evaluate the response of soil fauna to native and introduced insect-parasitic nematodes applied inundatively or via an insect cadaver, simulating a natural infection.
2) Evaluate the effects of tillage on the soil fauna response.
3) Evaluate the effects of time on the soil fauna response
Three strains of nematodes were used; one non-native commercial strain, Steinernema riobrave; and two nematodes native to the site, Steinernema carpocapsae, and Heterorhabditis bacteriophora. To simulate a natural infection, Greater wax moth larvae (Galleria mellonella) were innoculated with individual strains of nematodes, producing infected insect cadavers. Cadavers were placed in cages (biopsy cassettes) and buried in the soil. Nematodes applied inundatively were diluted in solution at the commercial rate.
At 4 hours and 24 hours after nematode application soil samples were collected and soil fauna extracted, enumerated and identified.
Collections included 115 taxa which occurred in patchy distribution and variable abundance. Data indicated a higher diversity and abundance of soil fauna in the no-till versus conventional-till soil. Diversity and abundance of most groups of soil fauna also increased from 4 hours to 24 hours.
Responses of soil fauna to the nematode treatments were not evident at the level of community abundance or diversity. Responses to nematode treatments, however, were evident at the level of community composition. Specific taxa of soil fauna responded to treatments containing nematodes, treatments containing native nematodes, and the treatment consisting of the non-native nematode. Key taxa of soil mites, including members of the Cunaxidae (Acari: Prostigmata), Histiostomatidae (Acari: Astigmata), Sancassania sp. (Astigmata: Acaridae) and several families of Mesostigmatid mites, were also found to exhibit particularly strong responses to the presence of nematodes. Sancassania sp. occurred in particularly large numbers and were also observed to feed on nematodes in lab assays. A marginal nematode treatment effect among several families of Oribatid mites was also observed, requiring further examination.
Further analyses, including repetition of experiments, are required to more accurately assess responses of specific taxa and how these responses may impact applied or augmented insect-parasitic nematode populations. Currently all field work has been completed. Collected samples are being assessed (approximately half have been assessed) and data analyzed as it is received. The remaining samples will be analyzed and quantified so that a complete report may be presented and published.
This data will provide basic information regarding soil fauna interactions relative to application and augmentation of insect-parasitic nematodes in different tillage regimes over time that is essential in developing holistic sustainable methods of pest management in agriculture. A summary of this project and findings, to date, was presented at the annual meeting of the Acarological Society of America in Montreal, Canada on December 9, 2000. The presentation was awarded the “Best presentation by a graduate student” award at the meeting.
Impacts and Contributions/Outcomes
Several presentations regarding this project have also been made at grower meetings, and a soils workshop conducted at the Center for Environmental Farming Systems (CEFS) near Goldsboro, NC.
North Carolina State University