Research Article |
Corresponding author: Radosław Ścibior ( radoslaw.scibior@up.lublin.pl ) Academic editor: Miguel Alonso-Zarazaga
© 2018 Radosław Ścibior, Jacek Łętowski.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Ścibior R, Łętowski J (2018) The morphology of the preimaginal stages of Rhinusa neta (Germar, 1821) and notes on its biology (Coleoptera, Curculionidae, Mecinini). ZooKeys 807: 29-46. https://doi.org/10.3897/zookeys.807.28365
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A detailed description of the mature larva and pupa of Rhinusa neta (Germar, 1821) and new diagnostic features of this species are presented. The development cycle of R. neta in the standard conditions lasts almost 60 days: an 11-day egg period, a 29-day larval period, and an 18-day pupal period, on average. The larvae are parasitised by hymenopterans of the superfamily Chalcidoidea. Similarities and differences with Rhinusa bipustulata and other species of this genus are presented.
Egg, host plant, life development, Linaria vulgaris , mature larva, parasitoid, Plantaginaceae , pupa, weevil
The taxon Rhinusa attained the rank of the genus based on the classification made by
Rhinusa neta is a species distributed mainly in southern and central Europe, also noted in Belgium, the Caucasus, Afghanistan, Kazakhstan, Iran, Algeria, and Morocco (
Rhinusa neta was introduced to the United States in 1937 and to Canada in 1957, and from the late 1950s, it was used in both countries for biological control of two species of toadflax (L. vulgaris and L. dalmatica). The primary host plant for R. neta in North America is L. dalmatica and the secondary host plant is L. vulgaris. R. neta is much less common in these countries and is found in more dispersed populations than the morphologically very similar R. antirrhini. When both species feed on Linaria at the same time, seed losses may reach 90% (
The aim of present paper is to describe development stages (mature larva L3 and pupa) of Rhinusa neta and collect a new diagnostic features of this species. Some data about biology are also presented.
Samples with flowering and fruiting Linaria vulgaris plants were collected from June to August in 2014–2016 in the following locations in the Lublin Upland (south-eastern Poland): Garbów (51°22'15.91"N, 22°21'25.82"E), unplowed strip between fields; Lublin (51°13'39.15"N, 22°38'31.43"E), lawn next to the street; Lublin (51°14'42.21"N, 22°32'12.93"E), ruderal vegetation next to tennis courts (UMCS campus); Niebrzegów (Bonów) (51°30'48.28"N, 21°57'03.43"E), meadow; and Mięćmierz (51°18'22.50"N, 21°54'15.80"E), unplowed strip between fields. Adults were collected from plants using a sweep net in series of 100 sweeps each time, at intervals of 3–7 days, from May to August on sunny, windless days, during the hours (10 am to 4 pm) where they are most active. To obtain preimaginal stages, the aboveground parts of Linaria vulgaris were collected for further detailed analysis in the laboratory. In total, ca. 520 specimens of the host plant were collected in the field and examined. The development stages (eggs, larvae, and pupae) were isolated from plants by making delicate cuts in the developing infructescence and extracting them from its interior. Some of the eggs and larvae (ten of both stages) were used for further breeding in the insectarium, and others were used for measurements (also ten) and microscope slides.
Developmental stages (L3) isolated from the generative parts were transferred to Petri dishes on an ongoing basis. Further breeding was carried out in accordance with recommendations by
Preparation of microscope slides of preimaginal stages and graphics. Larvae and pupae were treated with lactic acid C3H6O3 (80%). Smaller morphological structures (mouthparts) were first immersed in a cold KOH solution (5%) before being transferred to lactic acid. Developmental stages were analysed and documented using an OLYMPUS BX61 microscope at magnifications from 200× to 400×. All graphics for the study were prepared using CorelDraw X8 software. Metric data are means from ten measurements. Drawings of the morphological structures of the larva and pupa were based on microscope slides prepared according to
Setae of the thorax and abdomen of the larva (L3) and pupa are described for one side only.
Measurements (in mm). Egg length 0.47–0.51 (mean 0.49), width 0.25–0.29 (mean 0.27).
General. Oval, slightly oblate.
Colouration. Light yellow, smooth surface.
(Figure
General. Body massive, strongly curved.
Colouration. Head yellow-brown, body light yellow, covered with black, numerous setae.
Differences of the mature larva (L3) of Rhinusa neta and R. bipustulata based on the publications of
Rhinusa neta | Rhinusa bipustulata | |
---|---|---|
Frontal suture of epicranium | V-shaped | Y-shaped |
Endocarina | reaches 4/5 of frons | reaches 1/2 of frons |
Setae of head | des – 5, pes – 4 | des – 4, pes – 5 |
Stammata (ocelli) | well visible, larger | poorly visible, smaller |
Antennae | basal membranous area with 2 sensillae | basal membranous area with 7 sensillae |
Labrum, clypeus | clypeus with 2 cls and 1 sensilla | clypeus with 3 cls and no sensilla |
Mandible | mds – 3 | mds – 2 |
Maxillae | basal segment with 1 setae and 2 sensilla, distal segment with group of 10 short cuticular apical processes and 1 sensilla, | basal segment with 1 seta and 1 sensillum, distal segment with group of 4 long cuticular apical processes and 1 sensilla, |
Labial complex | prelabium oval, with 2 processes in basal part, ligs 2 pair in 2 rows, labial palps one-segmented with 5 conical cuticular apical processes (4 short, 1 long) | prelabium heart-shaped, with 1 process in basal part, ligs 2 pair in 1 row, labial palps one-segmented with 5 conical cuticular apical processes (5 short) |
Thorax (one side) | prothorax: prns on strongly sclerotised shield | prothorax: prns not on strongly sclerotised shield |
Abdomen (one side) | 8 unicameral spiracles located in middle of segments I–VIII, segments I–VII with 1 prs, 3 dpls, segment VIII with 1 dls, 3 dpls | 8 unicameral spiracles located at anterior margin of segments I–VIII, segments I–VII with 2 prs, 1 dpls, segment VIII – 1 prs, 1 dpls |
Vestiture. Cuticle with strongly chitinised spots in several places on dorsal side. Asperities of body integument present on the surface of all thoracic segments and first abdominal segment covering area occupied by a group of setae prns and pds. Analogous structure presents only on the surface of the first pedal lobe.
Head capsule (Figure
Mature larva (L3), epicranium, dorsal view: at – antenna, cls – clypeal seta, des – dorsal epicranial seta, enc – endocarina, es – epicranial suture, fs – frontal seta., les – lateral epicranial seta, lms – labral seta, st – stemmata, pes – posterior epicranial seta, vcs – ventral cranial seta.
Clypeus with two setae of equal length (cls1, 2) at base with one sensilla between them.
Mouthparts (Figs
Thorax (Figure
Abdomen (Figure
Mature larva (L3), selected segments, lateral view: as – alar seta, dls – dorsolateral seta, dpls – dorsopleural seta, ds – dorsal seta, ls – lateral seta, lsts – laterosternal seta, msts – mediosternal seta, pds – postdorsal seta, prs – prodorsal seta, prns – pronotal seta, ps – pleural seta, ss – spiracular seta, sts – sternal seta, ts – terminal seta, vpls – ventropleural seta.
(Figs
Colouration. Yellow-brown with distinct chaetotaxy.
Head (ventral view): rostrum reaches end of mesothorax, with one short seta (drs) apically. Head with distinct eyes and one seta (sos) at their inner edge. Antennae at base of rostrum. Massive. Thorax: pronotum wider than long, trapezoid-shaped, with two distinct, highly sclerotised, bare tubercles at anterior margin, with eight long setae: aps1–2, lps1–3, dps2, and bps1–2 (Figs
Pupa, lateral view: aps – apical pronotal seta, bps – basal pronotal seta, dps – discal pronotal seta, drs – distrirostral seta, fes – femoral seta, lps – lateral pronotal seta, msns – mesonotal seta, mtns – metanotal seta, pds – postdorsal seta, pls – pleural seta, pc – pseudocerci, sos – supraorbital seta, sp – spiracle.
Differences of the pupa of Rhinusa neta and R. bipustulata based on the publications of
Rhinusa neta | Rhinusa bipustulata | |
---|---|---|
Body | length 3.35 mm (mean), width (between the apex of mesofemora)1.92 mm (mean), yellow-brown | length 2.9–5.0 mm, width (between the apex of mesofemora) 1.50–2.60 mm, white or yellowish |
Head | rostrum with 1 seta (drs), head with 1 seta (sos) | rostrum with 3 setae – 2 drs, 1 es, head with 2 setae (brs) |
Thorax | pronotum: 8 setae: 2 aps, 3 lps, 2 bps, 1 dps, all femora with 1 long seta (fes) | pronotum: 9 setae: 2 aps, 3 lps, 2 bps, 2 dps, all femora with 2 long setae (fes) |
Abdomen | dorsal part of segments I–VIII with 4 setae of unequal length in one row and 2 of setae located laterally on pleural area III–VIII | dorsal part of segments I–VIII with 4 setae of unequal length in one group (3) and 1 seta located laterally and 1 seta on pleural area I–VIII |
ventral part of segments I–VIII with 4 of setae, of which 1 medial is longer and 3 shorter, arranged in row | ventral part of segments I–VII with 5 short setae distributed in regular lines | |
abdominal segment VIII with 4 setae of unequal length located dorsally, 1 lateral slightly shorter and 4 short setae located ventrally in regular line | abdominal segment VIII with 2 microsetae located dorsally and 2 short, thin setae located ventrally | |
abdominal segment IX without setae | abdominal segment IX with 3 microsetae located ventrally | |
pseudocerci (urogomphi) longer, clearly visible | pseudocerci (urogomphi) very short, poorly visible |
After overwintering, adults emerge in May and June, depending on weather conditions in the year (
In the last ten years a number of studies by various authors have described the larval and pupal morphology of several taxa of Curculionoidea (Curculionidae, Apionidae): Lixinae (
In the genus Rhinusa, the most detailed morphology of immature stages in Europe can be found only for the species R. bipustulata in a study by Gosik (2010). For the remaining, fragmentarily described species, the only such studies are publications by
A study by
The number of setae on the dorsal surface of mandible within the Curculionidae family usually varies from 0 to 2. On this surface, there are also sensillae in the number of 0 to 3. The mandible of the discussed taxon generally resembles the system present in Ceutorhynchinae in terms of the setae and sensillae system (
In regard to the characters contained in the key by
As regards the biology of species, in addition to Rhinusa taxa, data on R. pilosa have been published as well (
The information given in the two tables, grouping all available differences in the morphological structure of the L3 larva and pupa, can be used to prepare more detailed keys, both between the taxa given above and at the level of the tribe.
In the case of the pupae of the two taxa, the differences are in the number and location of the pairs of setae on the rostrum and head, number of pairs of setae on the prothorax, number of setae on the femora, location of the setae on the tergites, number of setae on the pleurites, number of setae on the sternites of segments I-IX, and length of the pseudocerci (or urogomphi).
Data presented by
The authors would like to thank Krzysztof Olszak, Mariola Maj, and Wioleta Maj for their help in collecting and analysing the biological material and the reviewers for considerably improving the manuscript.