Abstract
Studying plant-aphid interactions is challenging as aphid feeding is a complex process hidden in the plant tissue. Here we propose a combination of two well established methods to study nutrient acquisition by aphids focusing on the uptake of isotopically labelled nitrogen (15N). We combined the Electrical Penetration Graph (EPG) technique that allows detailed recording of aphid feeding behaviour and stable isotope ratio mass spectrometry (IRMS) to precisely measure the uptake of nitrogen. Bird cherry-oat aphids Rhopalosiphum padi L. (Hemiptera, Aphididae) fed for 24 h on barley plants (Hordeum vulgare L., cultivar Lina, Poaceae) that were cultivated with a 15N enriched nutrient solution. The time aphids fed in the phloem was strongly positive correlated with their 15N uptake. All other single behavioural phases were not correlated with 15N enrichment in the aphids, which corroborates their classification as non-feeding EPG phases. In addition, phloem-feeding and 15N enrichment of aphids was divided into two groups. One group spent only short time in the phloem phase and was unsuccessful in nitrogen acquisition, while the other group displayed longer phloem-feeding phases and was successful in nitrogen acquisition. This suggests that several factors such as the right feeding site, time span of feeding and individual conditions play a role for the aphids to acquire nutrients successfully. The power of this combination of methods for studying plant-aphid interactions is discussed.
Highlights
Aphids are significant agricultural pests and have a strong economic impact due to their phloem-feeding behaviour [1,2]
In this study we aimed to evaluate the combination of Electrical Penetration Graph (EPG) and 15N labelling to estimate the amounts of N acquired by aphids feeding on barley plants, and to relate the duration and frequency of aphid-EPG-feeding phases to these amounts
The complex feeding behaviour of aphids has been described in detail using the EPG technique through which different phases of aphid feeding can be specified [19,20]
Summary
Aphids are significant agricultural pests and have a strong economic impact due to their phloem-feeding behaviour [1,2]. Aphids feed on phloem sap, entering the sieve tube to obtain carbohydrates, amino acids, minerals, vitamins and macromolecules [3,4,5]. Plants have developed a wide variety of defence mechanisms, e. Plant defence metabolites that are mobile in the phloem sap include phytohormones, polyamines [3,10], speciesspecific secondary metabolites [11,12] and defence proteins [5,10,13,14]. Amino acids are the main nitrogen source for aphid growth and development, despite their low concentration in the phloem sap [15]. Aphids can increase their nitrogen supply by forming symbiotic relationships with bacteria [15,16] or by redirecting the plant’s nitrogen allocation [17]
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