Black Soldier Flies Help with Biological Control

Amending soils with wastes left from black soldier fly rearing is already well known to promote growth of different plants, including kale, mustard, grasses, and Brussels sprouts. It turns out that adding the skins cast by black soldier flies during molting (entomologists call them exuvia) to the soil also promotes parasitism of leaf-dwelling insect pests by their natural enemies. This ability also complements the earlier reported negative effects of black soldier fly frass on soil-dwelling insect pests and on weeds. It increasingly looks like black soldier flies may become an important component of integrated pest management plans that do not require as much insecticide use as is common in modern industrial farming.

van de Zande, E.M., Ojeda‐Prieto, L., Markou, A., van Leemput, J., van Loon, J.J. and Dicke, M., 2024. Enhanced parasitisation of caterpillars and aphids on field‐grown Brassica oleracea plants upon soil amendment with insect exuviae. Functional Ecology

  1. Multitrophic plant–insect interactions are mediated by plant volatiles. The emission of herbivore-induced plant volatiles is influenced by environmental conditions, such as soil microbes and nutrient composition, with consequences for above-ground trophic interactions. Here, we investigated whether insect exuviae in the soil alter the plant's volatile blend and attraction of parasitoids in the laboratory and whether this attraction also occurs in the field.
  2. We studied the effects of soil amendment with exuviae originating from three insect species, Tenebrio molitor, Acheta domesticus and Hermetia illucens, on the proportion of parasitised Plutella xylostella caterpillars and Brevicoryne brassicae aphids in the field in three consecutive years. In the laboratory, we collected and analysed the volatile blend of amended plants infested with caterpillars or aphids. The attraction of the parasitoids Diadegma semiclausum and Diaeretiella rapae, respectively, towards these volatile blends was assessed in an olfactometer.
  3. Our study shows that insect exuviae-amended soil enhanced the proportion of parasitised herbivores of two species in the field. Relative amounts of several components of the plant volatile blend were affected by soil amendment. Soil amendment with Acheta domesticus or Tenebrio molitor exuviae resulted in an increased attraction of the two parasitoid species in the olfactometer.
  4. Soil amendment with insect exuviae altered the plant volatile blend leading to enhanced attraction of parasitoids in laboratory assays. These effects were sustained under the complex and variable biotic and abiotic conditions in the field. Our results underline the importance of belowground processes, such as the decomposition of insect exuviae, on aboveground volatile-mediated multitrophic interactions.