Abstract
Infestation of willow plants by the giant willow aphid Tuberolachnus salignus (Hemiptera: Aphididae) is associated with copious deposition of sugar-rich honeydew under the plant canopy. We explored the effect of aphid honeydew on the soil biota and biochemical indicators in a two-year field trial. Soil samples from under aphid-infested and control willow trees, as well as samples from black sooty mould spots under the aphid-infested willows were compared; soil samples before aphid inoculation were used as a baseline. The honeydew deposition had a positive effect on the total soil carbon (C), but not on the total soil nitrogen content or soil pH. Microbial biomass C, basal respiration, number of yeast colony forming units, and the geometric mean of activities for six enzymes were significantly higher in honeydew-affected soils than in the control treatment on both years. The honeydew deposition also increased soil meso-fauna abundance, especially in the black sooty mould spots. The soil biochemical properties, which differed before and after aphid infestation, showed considerable overlap between the first and second year post-infestation. The results highlight the cascading effects of T. salignus on soil biological activity and the importance of using a multitrophic approach to explore similar scenarios.
Highlights
The giant willow aphid, Tuberolachnus salignus (Gmelin) (Hemiptera: Aphididae), is an invasive stem-feeding pest of willow trees, which has recently arrived in New Zealand [1]
We found that the copious deposition of honeydew on the soil surface affected the soil biological and biochemical properties, especially in the spots marked by the black sooty mould
The honeydew deposition could indirectly decrease the soil N content through enhanced microbial activity [15,75], where microorganisms could emerge as potential competitors of willow plants for nitrogen resources [76]
Summary
The giant willow aphid, Tuberolachnus salignus (Gmelin) (Hemiptera: Aphididae), is an invasive stem-feeding pest of willow trees, which has recently arrived in New Zealand [1]. One of the prominent features of infested willow plantings is the deposition of copious amounts of honeydew by aphid colonies, and the growth of black sooty mould on the leaves, stems, and on the soil surface ([1]; see Figure 1). The honeydew is a mixture of water, carbohydrates (90–95% dry weight), amino acids (
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