Using insect feed industry waste to control cabbage pest
Originally published on Farming Future Food.
Using the excrement and shed skins of black soldier fly (BSF) as a soil amendment could reduce the impact of the cabbage root fly, a troublesome pest affecting brassica growers, while making use of waste products from the alternative feeds industry.
In a series of experiments carried out at Wageningen University & Research in the Netherlands, scientists added the exuviae (shed skins) and frass (excrement) of a number of species of insects commonly farmed as alternative food and feed — BSF, house crickets and mealworm — to soil.
They planted brussels sprouts in the soils, then waited five weeks before introducing cabbage root fly (Delia radicum) larvae, to test effects on the pest’s survival and biomass, as well as crop germination and plant biomass. The novel soil treatments were compared to synthetic fertiliser.
Of the insect species, only the waste products of BSF showed potential as control agents. BSF excrement reduced the survival of D. radicum larvae, while their shed skins reduced larval biomass. Neither reduced the biomass of adult flies; however, the researchers suggested that this could be due to larvae with reduced biomass not completing their life cycle.
Control through microbe manipulation
With reduced synthetic pesticides available for control programmes, harnessing the power of microbial communities through novel soil amendments could provide a solution to losses caused by the pest, as part of an integrated pest management approach.
As for house cricket and mealworm waste products not having a negative impact on cabbage root fly survival or mass, the scientists offered a possible explanation.
“The colonization of black soldier fly, house cricket and mealworm residual streams by distinct bacterial communities seems likely, considering that these species belong to separate insect orders and are thus distantly related,” they wrote in Journal of Applied Entomology.
“By contrast, the black soldier fly and D. radicum are both insects of the order Diptera, which suggests that soil bacteria stimulated by black soldier fly residual streams might potentially colonize D. radicum, too.”
Unpredictable impacts on plant growth
Over the course of the study, amending soil with BSF reduced shoot biomass of the plants compared to synthetic fertiliser and mealworm, with the addition of house cricket wastes also affecting germination. However, adding BSF resulted in increased root biomass compared to mealworm.
More knowledge about the interactions between the microbial communities brought about through the addition of insect feed waste streams and plants is needed, the researchers said.
“Where introduced microbial agents may not persist long enough to provide effective crop protection, insect-derived soil amendments could indeed ensure the long-term establishment of naturally occurring biocontrol agents,” they continued.
“Nonetheless, the true mode of action of these amendments and their potential role as a substrate for beneficial soil microbes remain to be investigated.”
Further work should use genomic techniques to explore the microbial communities in amended soil, to make connections between different microbes and their effects on the pest, they added. Experiments under field conditions will also be needed.
