Occurrence of Panagrellus (Rhabditida: Panagrolaimidae) Nematodes in a Morphologically Aberrant Adult Specimen of Rhynchophorus ferrugineus (Coleoptera: Dryophthoridae)

Abstract

An aberrant specimen of Rhynchophorus ferrugineus (Coleoptera: Dryophthoridae) also known as red palm weevil (RPW), the most economically important insect pest of palms in the world, was found among a batch of conspecifics reared for research purposes. A morphological analysis of this weevil revealed the presence of nematodes associated with a structured cuticle defect of the thorax. These nematodes were not able to be cultured, but were characterized by molecular analysis using 28S and 18S ribosomal DNA and shown to belong to the family Panagrolaimidae (Rhabditida), within a clade of Panagrellus. While most nematodes in the insect were juveniles, a single male adult was partially characterized by light microscopy. Morphometrics showed similarities to a species described from Germany. Excluding the entomopathogenic nematodes (EPN), only five other genera of entomophilic or saprophytic rhabditid nematodes are associated with this weevil. This is the first report of panagrolaimid nematodes associated with this invasive pest. Possible mechanisms of nematode-insect association are discussed.Key words: insect thorax defect, invasive species, nematode phoresy, physiological ecology, saprophagous nematode, sour paste nematode.Rhynchophorus ferrugineus, the RPW, is currently considered as the most damaging pest of palm species in the world (Giblin-Davis et al., 2013). A recent review highlighted the paucity of data concerning the natural enemies and the organisms associated with the RPW (Mazza et al., 2014). Although new knowledge has been acquired in recent years, much remains to be done (Mazza et al., 2014). Excluding the EPN belonging to Steinernema and Heterorhabditis genera, few other insectassociated nematodes with entomophilic, saprobiotic, phoretic, commensal, or parasitic associations (Sudhaus, 2008) are known to be associated with this weevil. Those genera already identified include Acrostichus Rahm, 1928; Bursaphelenchus Fuchs, 1937; Caenorhabditis (Osche, 1952) Dougherty, 1953 Diplogasteritus Paramonov, 1952; Mononchoides Rahm, 1928, and Teratorhabditis (Osche, 1952) Dougherty, 1953 (reviewed in Troccoli et al., 2015. Further studies are necessary to identify weevil nematodes, clarify their biology and type of association with RPW, and consider their possible effects as biocontrol agents (Mazza et al., 2014). With this aim, we report the first finding of nematodes belonging to Panagrolaimidae (Nematoda: Rhabditida) associated with the RPW and briefly discuss the possible modes of association. MATERIALS AND METHODSOrigin and rearing of the RPW: Newly emerged RPW adults with a balanced sex ratio (n = 384) were provided by the UTAGRI-ENEA C.R. Casaccia, Laboratorio Gestione Sostenibile degli Agroecosistemi, Rome, Italy in 2013 to 2014. Larvae were individually reared, in a climatic room (298C, about 100% relative humidity with a photoperiod of 12:12), in plastic containers with perforated lids, fed with apple slices, and incubated until adult emergence. Final larval instars made cocoons using coc...

Molecular profiling of nematode associates with Rhynchophorus ferrugineus in southern Italy

“…The sequence of the D2‐D3 expansion domains of the rhabditids showed a 100% similarity with Panagrellus sp. recovered from R. ferrugineus in Tuscany, and from decaying pomegranate in association with the nematode Sheraphelenchus sucus in Apulia (Camerota et al, ; Fanelli et al, ).…”

“…Apart from the two phoretic nematode species found in this study, other nematode species were also occasionally associated with R. ferrugineus. Of these, Oscheius tipulae (Lam & Webster, 1971), Sudhaus, 1993 (Camerota et al, 2016;Fanelli et al, 2017).…”

“…Associations between Rhynchophorus species and nematodes are well documented for R. palmarum (L.) and R. cruentatus (F.), but very little is known about R. ferrugineus with regard to its fitness, evolution, coadaptation, speciation, defense, chemical communication, or pest management (Camerota et al, 2016;Esparza-Diaz, Olguin, Carta, Skantar, & Villanueva, 2013;Giblin-Davis et al, 2013;Kanzaki & Giblin-Davis, 2018). Nematodes are microscopic worms that are adapted to living in a variety of environments, and many can be associated with other organisms that provide them with shelter or transportation, for example, entomophilic, saprobiotic, phoretic, commensal, and parasitic nematodes (Kanzaki, 2017).…”

Pristionchusnematodes occur frequently in diverse rotting vegetal substrates and are not exclusively necromenic, whilePanagrellus redivivoidesis found specifically in rotting fruits

“…Its 28S rDNA sequence is identical to that of a Panagrellus sp. found in decomposing pomegranate in Italy [53] and both 28S and 18S sequences are similar but not identical to that of a Panagrellus found in a weevil in [61]. A new species of Panagrellus has been very recently described from a culture of Drosophila melanogaster and called P. levitatus [62].…”

Occurrence of Sheraphelenchus sucus (Nematoda: Aphelenchoidinae) and Panagrellus sp. (Rhabditida: Panagrolaimidae) Associated with Decaying Pomegranate Fruit in Italy

“…from pomegranate showed 99% similarity (8 nucleotide different) with Panagrellus sp. isolated from aberrant adult specimen of R. ferrugineus (Camerota et al, 2016). Thus, selected Panagrellus and rhabditid sequences were aligned with those of D2-D3 of Panagrellus sp.…”