Electrically recorded feeding behaviour of cassava mealybug on host and non‐host plants

Abstract

The feeding behaviour of cassava mealybug (Phenacoccus manihoti) was analysed by the electrical penetration graph technique (EPG, DC‐system) and by light microscopy. This study confirmed a typical phloem‐feeding behaviour with an aphid‐like predominance of extracellular pathways of stylets. Similarities of EPGs from mealybugs with those of aphids and whiteflies allowed adoption of standard pattern labelling. The main differences with aphid EPGs consisted of fewer but longer intracellular punctures (pd duration of 20 s vs 5–7 s for aphids), longer times to the first phloem‐ingestion period and a lower motility of stylets within the phloem searching process. Comparison of the feeding behaviour on 6 plant types, including two occasional hosts (Talinum and poinsettia), one cassava hybrid and three common cassava cultivars (Manihot esculenta), allowed differentiation of penetration profiles. Intracellular punctures were shorter on occasional hosts, on which phloem finding and subsequent ingestion were markedly delayed although a great variability within plants persisted. Chemical analysis of some secondary plant substances revealed that none of the plants tested contained detectable amounts of alkaloids, and that cyanides were restricted to true hosts (cassavas and Manihot hybrid). Levels of total flavonoids did not differ between hosts and non‐hosts, in contrast to those of phenolic acids. Preliminary correlations with EPG patterns are discussed. Résumé Le comportement alimentaire de la cochenille du manioc (Phenacoccus manihoti) a été étudié par électrographie de pénétration (EPG, analyse en courant continu) et par microscopie optique. Cette étude a permis de confirmer le caractère typiquement phloémophage de l'alimentation de cet Homoptère, présentant une large prédominance du trajet extracellulaire des stylets, comme cela est également observé chez les pucerons. Les similitudes des tracés EPG effectués sur cochenille et sur pucerons ou aleurodes ont permis d'adopter la même typologie du signal. Les principales différences avec les pucerons concernent le nombre moins important et la durée plus longue des ponctions intracellulaires (20 s en moyenne contre 5 à 7 s chez les pucerons), l'allongement du temps d'accès au phloème et une moins grande mobilité des stylets lors de la phase de recherche du phloème. La comparaison du comportement alimentaire sur 6 plantes, parmi lesquelles deux hôtes occasionnels (Talinum et poinsettia), un hybride et trois variétés courantes de manioc (Manihot esculenta), a permis de différencier plusieurs profils de pénétration. Les ponctions intracellulaires se sont révélées plus courtes sur hôtes occasionnels, qui induisent également, malgré la variabilité observée, un allongement net de la période de localisation du phloème et donc un retard à l'ingestion. Aucune des plantes testées ne contient d'alcaloîdes, et les composés cyanés se restreignent au genre Manihot, hôte naturel de la cochenille. Les flavonoîdes totaux ne permettent pas de distinguer plantes hôtes et non‐hôtes, à l...

Probing behavior of Dysmicoccus brevipes mealybug in pineapple plants1

“…Thus, "drinking" in the xylem would only contribute to the insects water balance, and benefit only those insects experiencing water deficits (Spliller et al 1990). Mealybugs feed on phloem sap, from which they obtain carbohydrates and other nutrients (Calatayud et al 1994, Polania et al 1999. No significant differences were found between the cultivars, when the pathway period and xylem phase were analyzed together (Table 1, parameter 6), confirming that the mealybug stylet penetration through plant tissues was similar for both cultivars.…”

“…Which phenolic compounds exist in the intercellular spaces is unknown, although there is some evidence that phenolic acids and flavonoids are present in extracellular fluids and in the phloem (Calatayud et al 1994). Moreover, whether sucking insects can ingest intercellular fluids is either unknown or known to a very limited extent.…”

“…Waveforms and patterns were classified according to the system described by Calatayud et al (1994), Santa-Cecília (2003) and Cid & Fereres (2010). Probing behaviors consisted of 62 parameters related to feeding events, but only those considered relevant to the specific objectives of this research are presented here: number of probes, non-probing time, time to the first probe, pathway phase (pattern "C"), xylem phase (pattern "G"), pathway + xylem phase, mealybugs showing phloem phase, phloem phase (pattern "E"), time to reach the phloem phase from the first probe, time to reach the phloem phase in the probe and hours until the phloem is reached.…”

“…This technique has been previously used to study the probing behavior of several sucking insects (Calatayud et al 1994, Kindt et al 2006, Miranda et al 2009, Cid & Fereres 2010, Lazzarotto et al 2011, Liu et al 2013, Moraes et al 2013, Santa-Cecília et al 2013, plant resistance (Crompton & Ode 2010) and viral transmission (Tjallingii & Prado 2001, Fereres & Moreno 2009). …”

“…For example, plant cells often contain toxic compounds that can deter the insect probing behavior and, therefore, be used as a defense against pathogens (Miles & Oertli 1993). Calatayud et al (1994), for instance, reported that phenols produced by cassava cultivars alter the probing behavior of the cassava mealybug (Phenacoccus manihoti MatileFerrero).…”