The probing behaviour of the planthopper Delphacodes kuscheli (Hemiptera: Delphacidae) on two alternating hosts, maize and oat

Abstract

Delphacodes kuscheli is the most important natural vector of Mal de Río Cuarto virus (MRCV) in Argentina, a Fijivirus (Reoviridae) that causes important economic losses on maize production. Although this planthopper does not breed successfully on maize, virus transmission occurs when adults migrate from oat, a winter host and a reservoir of the virus, to maize. Probing behaviour on both hosts was recorded and analysed using the direct current electrical penetration graph (DC-EPG) system. Eight main waveforms were identified during probing behaviour by D. kuscheli. These waveforms were interpreted with reference to that described for delphacids and were related to putative probing activities: np (non-penetration or non-probe); N1, N2 and N3 (stylet pathway: penetration, salivation, stylet movement and extracellular activities near the phloem region); N4-a (sieve element salivation); N4-b (phloem sap ingestion); N5 (xylem activity); and N6 (derailed stylet mechanics). The EPG variables showed that on maize, D. kuscheli exhibited longer periods of non-probe and longer time from first probe to first phloem activity, with a higher percentage of probing spent in stylet pathway and xylem phase than on oat. Furthermore, on maize, fewer insects showed phloem phase activities (N4-a and N4-b) and sustained phloem ingestion than on oat, and the time on phloem ingestion was shorter than on oat. The constrained behaviour of D. kuscheli on maize suggests that plant resistance factors may be involved.

Probing behavior of the corn leafhopperDalbulus maidison susceptible and resistant maize hybrids

“…The reduction of total probing time due to shorter probes, despite an increase in the number of probes found here in DK390 for D. maidis, is similar to previous findings in the leafhoppers Nephottetix virescens [21,30] in rice, and Graminella nigrifrons [38] and Psammotettix alienus [39] in several hosts, the planthoppers Nilaparvata lugens [31,33,40] in rice, and Delphacodes kuscheli [41] in corn and oats, and the aphids Myzus persicae [42] in oilseed rape, Rophalosiphum padi [29] in barley, Acirthosiphon pisum [43] in pulse species, and Aphis glycines [44] in soybeans. This behavior is observed as insects reject either non-hosts species or resistant genotypes before they contact phloem, implying that factors conferring plant resistance of the antixenosis type are located at the epidermis or mesophyll.…”

“…However, the time spent on phloem salivation was not increased in these hybrids, as in earlier studies of the leafhoppers N. virescens [30] and G. nigrifrons [38], but disagreeing with the findings in the planthopper N. lugens [31] and the aphid M. persicae [46], which found an increase of the total time spent on salivation in resistant genotypes. Yet another aspect depicting a resistance factor located in phloem was seen as the first phloem ingestion was deferred in the resistant hybrids DK390 and DK72-10, similarly to the one described in the planthopper D. kuscheli [41] and the aphids M. persicae [42,46], and R. padi [29], although the time to first phloem contact in the planthopper N. lugens [33] was similar both in resistant and susceptible rice varieties.…”

“…Insects with access to DK390 spent less time ingesting from phloem as compared to the other hybrids. This behavior of resistant genotypes or non-host species has been found in other species, such as the leafhoppers G. nigrifrons [38] and N. virescens [30,21,28], the planthoppers D. kuscheli [41] and N. lugens [40,31], and in the aphids A. glycines [44,45], A. pisum [43], M. persicae [42,46] and R. padi [29]. Another aspect to consider regarding phloem ingestion is the proportion of insects reaching this stage.…”

Endomycobiome associated with females of the planthopper Delphacodes kuscheli (Hemiptera: Delphacidae): A metabarcoding approach

“…The presence in D. kuscheli of fungi frequently reported as endophytic and associated with the phylloplane and digestive tract of insects, suggests that the feeding behaviour might be one of the ways that this planthopper acquires at least several of these fungi. Delphacodes kuscheli repeatedly explores the plant surface with the labium and secretes a small amount of saliva to dissolve and test chemical components, which is followed by extensive periods of salivation and ingestion in phloem sap ( Brentassi, 2004 ; Brentassi et al., 2019 ). This behaviour may lead to the ingestion of fungi that inhabit the phylloplane as well as fungal endophytes associated with their gramineous host plants.…”

“…Delphacodes kuscheli Fennah (Hemiptera: Delphacidae), a species whose generic status is under revision, is a multivoltine species widely distributed in Argentina (latitude 32°–35° S) ( Remes Lenicov and Paradell, 2012 ). This planthopper is a phloem feeder ( Brentassi, 2004 ; Brentassi and Remes Lenicov, 2007 ; Brentassi et al., 2019 ) and is the most important natural vector of Mal de Río Cuarto virus (MRCV) (Fijivirus, Reoviridae) ( Remes Lenicov et al., 1985 ). MRCV seriously affects maize ( Zea mays L.) production in northern and central provinces of Argentina ( Lenardón et al., 1998 ; Giménez Pecci et al., 2012 ) and also has been detected in Uruguay ( Ornaghi et al., 1999 ).…”