Effects of biochar amendment to soils on stylet penetration activities by aphid Sitobion avenae and planthopper Laodelphax striatellus on their host plants.

Abstract

To understand why biochar amendment to soils has a negative effect on sap-feeding insects on their host plants, we used the electrical penetration graph (EPG) technique to examine probing and feeding behaviors of the English grain aphid Sitobion avenae on wheat and the small brown planthopper Laodelphax striatellus on rice; their food plants were cultured in soils receiving different treatments of biochar type (derived from three different types of feedstock: wheat, corn or rice straw) by amendment rate (four levels: 0, 1.5%, 3%, or 5%). In addition, we analyzed the contents of key nutrients in the wheat plant to explore their relevance to aphid feeding activities. Biochar amendment to soils increased the number of events and duration of non-probing and probing-preparation activities while decreasing the duration of stylet penetrations in the phloem sieve by both S. avenae and L. striatellus. The effect varied depending on the biochar amendment rate in S. avenae and on both biochar type and amendment rate in L. striatellus. Biochar amendment decreased the content of sucking stimulatory nitrogen and increased that of sucking inhibitory silicon and potassium in wheat plants; this effect varied with biochar amendment rate and not with biochar type. Biochar amendment can make stylet penetration activities less effective by S. avenae and L. striatellus on their host plants. Ineffective penetration may result from the alteration in the contents of penetration-relevant nutrients in the host plant as a consequence of biochar amendment to soils. © 2019 Society of Chemical Industry.