Scientists working on a US Government-funded project have uncovered some of the best substances to protect nematode species used in agricultural pest control from the damaging effects of ultraviolet radiation — with a few from surprising sources.
In lab experiments, researchers led by Shaohui Wu at the University of Georgia tested a number of potentially- protective substances, which included laundry aids, fire retardants and a substance used in nappies. They individually mixed the materials with juvenile nematodes, first in screening tests with Steinernema carpocapsae, then also with Heterorhabditis floridensis, in solutions with distilled water at different concentrations.
They placed the formulations under a UV light for either 10 or 20 minutes, then incubated them for 24 hours, before analysing the nematodes under a microscope to assess their viability following the UV exposure and testing their effectiveness in infecting the larvae of the wax moth Galleria Mellonella.
Laundry starch and clay show promise
They found that liquid starch, which is typically used for ironing clothes after laundry, provided the highest level of protection to both the nematode species, albeit with a stronger effect for S. carpocapsae, which proved to be more UV resistant overall than H. floridensis. The next most effective substance was white kaolin clay, often used in the manufacture of porcelain, while Barricade, a product more widely known as a gel fire retardant, increased the viability of the nematodes but did not help in making them more able to infect the wax moth larvae.
Higher concentrations of liquid starch provided better protection, they found, but longer periods of exposure to UV still negatively affected the number of juvenile nematodes that infected the target insects.
Early screening tests as part of the study also served to seemingly rule out a number of substances as potential nematode protectors, with products including a paint remover and an artificial snow mix revealed as ineffective.
“This is the first study reporting the potential use of liquid starch for improving the activities of EPNs in pest management programs, a dramatically different purpose from the labelled use,” the researchers wrote in the journal Biological Control.
“In addition, the material may be used as an additive or adjuvant to other entomopathogenic nematode formulations, and the low cost will be a supplemental benefit of the material to be potentially adopted by growers.”
Outdoor testing brings different results
Following the lab testing, the researchers moved on to test the protection of the substances outdoors and in soil, with some different findings. Here, while liquid starch and kaolin clay did still show protective qualities, they were outperformed by Barricade and watergel, an absorbent polymer used in nappies.
They suggested that this may have been due to the soil protecting the nematodes from direct sunlight, while the heat of the outdoors made desiccation a greater issue, from which Barricade and watergel provided more effective protection.
Nematodes are a commonly used tool in integrated pest management programmes, used in different agricultural settings, from soil drenches to being sprayed on trees. This means that field exposure to both UV and the desiccating effect of warm air can greatly differ.
“It can be hypothesized that combining an UV protectant such as liquid starch with an anti-desiccant (Barricade or watergel) would boost the field persistence of entomopathogenic nematodes, which needs to be verified in future tests,” they added.