Anthonomus (Anthonomidius) rubripes Gyllenhal, 1835

Zabulev, Ilya A., 2021, Contribution to the knowledge of the immature stages of Palaearctic species of the genus Anthonomus Germar (Coleoptera: Curculionidae), Zootaxa 5032 (4), pp. 451-488 : 457-462

Anthonomus (Anthonomidius) rubripes Gyllenhal, 1835

Figs. 18–36 , 99–100 .

Material examined. 18 larvae (23.05– 4.06.2021) and 2 pupae (4.06.2021), Russia, Saratov region, near Sinenkiye vill. (51.244222°N 45.745267°E), ex buds of Potentilla argentea L. and P. bifurca L., leg. and det. I.A. Zabaluev ( IZCS); 7 larvae and 6 pupae — 28.05.2021, Russia, Saratov region, near Popovka vill. (51.426389°N 45.577401°’E), ex buds of P. bifurca , leg. and det. I.A. Zabaluev ( IZCS).

Description of mature larva. Figs. 18–28 .

Measurements (in mm). Body length: 1.89–2.73 (mean 2.31). Body width: 0.93–1.24 (mean 1.11). Head width: 0.47–0.56 (mean 0.52).

Body from white to yellowish, moderately C-shaped curved ( Fig. 18 ). Pronotum with a poorly visible yellowish compacted shield. Spiracles ( Fig. 19 ) bicameral, air tubes with six to eight annuli, one pair located on the prothorax and eight pairs located laterally on the abdominal segments I–VIII (Ab1–8). The setae of thoracic and abdominal segments are very fine, hairlike, from very long to short, yellowish. Prothorax (Th1) ( Fig. 20 ) with eleven prns of unequal length (prns 1 and prns 6 —short, other—from long to very long), two very long ps equal length and two eus (minute and long). There are two distinct sensilla: one located near the base of prns 1, the other—medially. Meso- (Th2) and metathorax (Th3) ( Fig. 20 ) with three prs (one medium and two minute), four pds different in length (pds 1 and pds 3— very long; pds 2 and pds 4 —short), one very long as, three ss (one long, one short and one minute), one very long eps, one long ps and two eus (long and minute). Pedal lobe with five pda different in length: pda 1 - 4 long, pda 5 minute and located close to the anterior edge of the segment. Abdominal segments I–VIII (Ab1–8) ( Fig. 21 ) with two prs (short and minute), five pds different in length (pds 1, pds 3, and pds 5 —long; pds 2 and pds 4 —short), three ss (one long, one very short and one minute and hardly noticeable), two eps (short and long), one very short ps, one very short lsts and three minute eus. Abdominal segment IX (Ab9) ( Fig. 22 ) with six setae dorsally (ds), two ps and two sts. Abdominal segment X (Ab10) without setae.

Head capsule ( Figs. 18 , 23 ). Endocarinal line present, reaching behind middle of the frons and about 2/3 as long as frons. Frontal sutures distinct, extending to antennae. One stemma (st) present close to antenna. Dorsal setae (five des): des 1 and des 2 long, des 3 and des 5 very long, des 4 short and fine; des 3 located close to frontal suture, des 2 —in front of the posterior part of epicranium, des 4 on laterally of des 3, des 5 —anterolaterally. There is one dorsal sensillum between des 4 and des 5. Frontal area with four fs: fs 1 and fs 3 minute, fs 2 absent, fs 4 very long, located anterolaterally, fs 5 very long, but slightly shorter than fs 4, located laterally, close to the border of frons, and with two sensilla—one is between fs 1 and fs 3, the other is between fs 4 and fs 5 slightly displaced towards the frontal suture. Lateral setae: les 1 short, les 2 very long. Ventral setae: vcs 1 short, vcs 2 medium, 2.5x as long as vcs 1. Posterior epicranial area with four minute pes arranged in a row, and with two sensilla—one is between pes 3 and endocarinal line and the other near des 1. Antenna ( Figs. 24 , 99 ) is one-segmented, consisting of a basal membranous segment bearing a short-conical porous sensorium (se) and six sensilla: one ampullacea (sa), four styloconium (ss) and one basiconicum (sb).

Clypeus and mouthparts. Clypeus ( Fig. 25 ) trapezium - shaped, with two cls placed close to anterior margin of frons and one clypeal sensillum (clss) located between them; cls 2 about 2/3 as long as cls 1. Labrum ( Fig. 25 ) with three lrs: lrs 1 and lrs 2 long, subequal length, lrs 3 short, about 1/3 as long as lrs 1. Epipharynx ( Fig. 26 ) with one long ams, three als, and two short mes. Labral rods (lr) moderately long, converging slightly posteriorly. One sensillum located on both sides of lr and four sensilla (esc), combined in two clusters with two pores in each. Mandibles ( Fig. 27 ) slightly elongated, strongly sclerotized, triangular, with two apical teeth, mds 1 and mds 2 medium, approximately equal length, mandibular sensillum located medially. Maxilla ( Fig. 28 ) with one long stps, two long pfs, very short mbs, and three sensilla. Mala on the dorsal side with a row of six finger-like dms, on the ventral side with four vms (two comparatively long and two short). Maxillary palpi consist of two palpomere: basal palpomere almost square, with one short mxps and two sensilla, distal—elongated, with one simple sensillum, one digitiform sensillum (sd) laterally, and eleven basiconicum sensilla (sb) at the apex ( Fig. 100 ). Prelabium cup-like with four sensilla and one medium prms; ligula with three ligs. Labial palpi elongated, one-segmented, with one sensillum and nine basiconicum sensilla (sb) at the apex. Postlabium with three pms: pms 1— medium, about as long as pms 3, pms 2 — very long, pms 3— medium.

Description of pupa. Figs. 29–31 .

Measurements (in mm). Body length: 2.11–2.71 (mean 2.36). Body width: 0.91–1.24 (mean 1.07). Head width: 0.44–0.53 (mean 0.48).

Coloration. Initially yellowish-white, turns more yellow over time. Setae (including the tubercles on which they are placed) and urogomphi are light brown.

Body. Rostrum long and stout, 4.0–4.5x as long as wide. Pronotum transverse, 1.4x as wide as long. Prothoracic depressions (pd) well defined, partially covered with antennae. Spiracles well developed on Ab1–5, and vestigial on Ab6.

Chaetotaxy. Setae from minute to long, slightly curved, light brown, like the tubercles to which they are associated. Head capsule with one vs, one os and one sos; vs distinctly curved, 1/2 as long as the width of the rostrum at the base, os slightly shorter and thinner than vs; sos even shorter and thinner than os. Rostrum with one rs and one pas; rs very short, fine, located anterior to the base of the antennae, about 1/5 as long as the rostrum width at the same place; pas as long as rs, located very close to each other at the base of the rostrum. Pronotum (Th1) with one as, two ds, two sls, and three pls; all setae short, slightly different in length, but sls 1–2 relatively more stout, whereas ds 1–2 thinner; as 1 located on small flat tubercles; ds 1 located subapically on the anterior surface of large conical tubercles, which larger than those elsewhere on pronotum; ds 2 —in front of the middle of spiniform tubercles, pls 1 —at the base of small rounded tubercles, pl s 2–3 —on small flat tubercles. Femora without fes. Meso - (Th2) and metanotum (Th3) with three rather long and stout dorsal setae (d) placed medially, on mesonotum they located without obvious tubercles, on metanotum—on small flat tubercles. Abdominal tergites (Ab1–8) with three distinct dorsal setae (d), d 1 shorter than others, d 2 and d 3 approximately equal length, the length of the dorsal setae gradually increases towards the apex of the abdomen, d 2 on Ab1–4 located without obvious tubercles, on Ab5–8 located at the bases of sharply pointed tubercles, d 3 on Ab1–3 located at the apex of flat tubercles, on Ab4—at the base small round tubercles, on Ab5–8—at the bases of large spiniform tubercles and the size of these tubercles is almost the same as in lt 2 on the corresponding segments. There are minute and inconspicuous dorsal setae between d 1 and d 2 and between d 2 and d 3 (although on Ab7–8 these setae can be distinguishable at 45x magnification). Lt 1 minute, on Ab1–3 located without obvious tubercles, on Ab4–8—at the bases of a small sharply pointed tubercles; lt 2 from long (on Ab1–4 and Ab7–8) to very long (on Ab5–6), located at the bases of large spiniform tubercles; l s absent. Ab9 with four fine setae: d 1 very short, located dorsally; d 2 minute, located dorsally; lt very short, located laterally, v very short, located ventrally. Urogomphi paired, sclerotized, short (slightly longer than its base width), slightly diverging, pointed at the apex.

Biological observations. In the south of the European part of Russia, this species is very common in steppe and meadow-steppe biotopes, along roads, on dry slopes, and wastelands ( Fig. 32 ). It develops on Potentilla argentea ( Dieckmann 1968) and P. bifurca ( Zabaluev 2016, listed as A. germanicus Dieckmann, 1968 ; misidentification). The first beetles were recorded on May 9, and the largest number observed in the second half of May. The adults feed on the leaves of Potentilla , making small dimples in the parenchyma ( Fig. 33 ). Oviposition occurs at the base of the bud ( Fig. 34 ), where a small dark spot remains. The egg is oval, white, translucent, 0.52–0.56 mm long, 0.36–0.38 mm wide ( Fig. 35 ). Due to the fact that Potentilla flowers bloom gradually over about a month, and not simultaneously, the oviposition period is extended, I found both eggs and larvae of different instars at the same time. Weevil-infested buds remain closed, but do not turn brown or dry out. An interesting observation in laboratory conditions was made on P. argentea , which has a dense corymbose multi-flowered inflorescence consisting of buds of different sizes. The larva (usually 2 nd or 3 rd instar) having destroyed the contents of one bud, gnaws a hole in its lateral wall and goes outside, feeds in the intervals between the buds, damaging the peduncle and adjacent buds ( Fig. 36 ). However, for pupation, the larva necessarily penetrated into the bud, and the hole sealed with a dense plug formed by larval excrement mixed with plant debris. This behavior was not observed during development on P. bifurca , which the flowers are located relatively farther from each other. Larvae of the minute pirate bugs Orius sp. ( Hemiptera , Anthocoridae ) were found feeding on the weevil larvae. The new generation of beetles started from June 10.

Figures

FIGURES 18–22. Anthonomus rubripes, mature larva. 18—habitus of the body and frontal view of head, 19—thoracic spiracle, 20—lateral view of thoracic segments, 21—lateral view of abdominal segment I, 22—lateral view of abdominal segments VIII–X (setae: as—alar, ds—dorsal, eps—epipleural, eus—eusternal, lsts—laterosternal, pda—pedal, pds—postdorsal, prns— pronotal, prs—prodorsal, ps—pleural, ss—spiracular, sts—sternal).

FIGURES 23–28. Anthonomus rubripes, mature larva head and mouthparts. 23—head, frontal view, 24—antenna, 25—clypeus and labrum, 26—epipharynx, 27—left mandible, 28—maxillolabial complex, ventral aspect (apical part of the right maxilla is shown in dorsal aspect) (at—antenna, clss—clypeal sensilla, lr—labral rods, esc—epipharyngeal sensilla cluster, st—stemma; setae: als—anterolateral, ams—anteromedial, cls—clypeal, des—dorsal epicranial, dms—dorsal malar, fs—frontal, ligs—ligular, lrs—labral, ls—lateral epicranial, mbs—basiventral malar, mds—mandibular, mes—median, mxps—maxillary palp, pes— postepicranial, pfs—palpiferal, pms—postlabial, prms—prelabial, stps—stipal, vms—ventral malar).

FIGURES 29–31. Anthonomus rubripes, pupa habitus and chaetotaxy. 12—ventral view, 13—dorsal view, 14—lateral view (Th1–3—number of thoracic segments,Ab1–9—number of abdominal segments, msa—metathoracic sclerotized area, pd—prothoracic depression; sp—spiracle; setae: as—apical, d—dorsal, ds—discal, lt—laterotergal, os—orbital, pls—posterolateral, sls—superlateral, sos—superorbital, v—ventral, vs—vertical).

FIGURES 32–36. Anthonomus rubripes, biotope and biology. 32—biotope (Saratov region, Sinenkiye), 33—P. argentea leaf damaged by adults, 34—oviposition, 35—egg, 36—the last instar larva inside of P. argentea inflorescence.

FIGURES 98–106. Antennae and maxillary palpi of Anthonomus (SEM images). 98—A. pinivorax, 99—antenna of A. rubripes, 100—maxillary palp of A. rubripes, 101—A. incurvus, 102—A. conspersus, 103—A. latior, 104—A. pedicularius, 105—A. pomorum, 106—A. rubi (se—sensorium, sa—sensilla ampullacea, sd—sensilla digitiform, ss—sensilla styloconium, sb—sensilla basiconicum). Scale bars 10 μm.