entirely occupied with water (i.e., in saturated soil), nematode drive
is restricted. Infective juveniles (IJs) can endure in low moisture
conditions by lowering their metabolic rate. Steady withdrawal of
water from the IJs allows them time to acclimatize to the dehydrating conditions. Natural soils thus cause the IJs to persevere longer
in dry soil. IJs can survive drying conditions by lingering within the
host cadaver before the soil moisture circumstances improves.
Water potential is estimated in kilopascals (kPa), where the
maximal water potential (pure water) is 0 kPa and lower water
potential negative.
Soil Water Potential
Purpose: To evaluate the range of soil water potential in which IJs
can seek and infect the host.
Materials Required
l
Plastic tubes.
l
IJs.
l
G. mellonella larva.
l
Sand.
l
Distilled water.
Procedure
1. Take 2 g of sand in plastic tubes and inoculate with 1000 IJs in
10 μl of sterile distilled water.
2. Assess the potential soil moisture (% w/w soil water content)
(e.g., 5.5 kPa (13%), 14 kPa (33%), 43 kPa (100% field capacity), 58 kPa (133%), and 73 kPa (166%)).
3. Introduce a G. mellonella larva in each container for a period of
48 h.
4. Dissect the larvae after the incubation period.
5. Count the number of living IJs established in the host and
mortality rate.
Soil Moisture
Purpose: To determine the survival of IJs in soil moisture to infect
the host.
Materials Required
l
G. mellonella larva.
l
IJs.
l
24-Well plates.
l
Soil.
l
0.5% Pepsin solution.
l
Cellophane tape.
102
Laboratory Techniques for Entomopathogenic Nematodes