Description of the mature larva and pupa of Anthonomus santacruzi Hustache (Coleoptera, Curculionidae), a biological control agent of Solanum mauritianum Scop. (Solanaceae), and remarks about its biology Author Gosik, Rafał Author Sasa, Archbold Author Witkowski, Ed. T. F. text Zootaxa 2017 4294 5 545 558 journal article 32556 10.11646/zootaxa.4294.5.4 3b35e5dc-6ec2-4d24-bfbf-a12530ed023a 1175-5326 839174 831A0613-4C48-49B6-A68C-C4539C3F9913 Description of the mature larva of Anthonomus santacruzi General. Body elongated, slightly curved ( Fig. 2 ), rounded in cross section. Colouration. Pale to dark brown head ( Figs 2 , 10 ). Thorax and abdomen white to whitish yellow ( Fig. 2 ). Vestiture. Setae on body thin, yellow or brown, of distinctly different lengths (minute to short or relatively elongate). Body shape ( Fig. 2 ). Prothorax smaller than meso- and metathorax (both with similar size). Spiracle bicameral, located on prothorax. Abdominal segments ĪV subequal in length; VĪVIII with length decreasing gradually posteriorly; IX almost hemispherical; X reduced to four anal lobes; dorsal anal lobe narrow; laterals lobes distinct; and ventral lobe very small. Anus terminal. Abdominal ambulatory ampullae bilobate to circular. Abdominal spiracles I–VIII bicameral, placed mediolaterally. Chaetotaxy. (Number of setae is given for only one side of the body.) Prothorax ( Figs 4, 6, 8 ) with 9 long and 2 medium prns1‾11 on a weakly pigmented dorsal sclerite; 2 ps1-2 , and 1 minute eus . Mesothorax ( Figs 4, 6, 8 ) with 3 long and 2 medium pds1‾5 (1, 3, and 5 long, 2 and 4 medial); 1 short as ; 1 medium eps ; 1 long ps and 1 minute eus . Metathorax ( Figs 4, 6, 8 ) similar to mesothorax. Each thoracic pedal area well separated, and with 2 long pda1‾2 . Abdominal segments ĪVIII ( Figs 4–9 ) with 1 short prs ; 3 long and 2 medium pds1‾5 (1, 3, and 5 long, 2 and 4 short); 1 long sps ; 1 long and 1 minute eps1‾2 ; 1 medium ps ; and 2 minute eus . Abdominal segment IX ( Figs 4 ̄9) with 5 ds (1 minute, 2 and 3 medium, 4 and 5 minute), 2 ps1‾2 (1 long, and 1 minute) and 1 very short sts . Abdominal segment X ( Figs 4 ̄9) without setae. Head capsule ( Fig. 10 ). Head hypognathous, suboval; endocarinal line present and reaching behind middle of frons. Frontal sutures distinct, extending to antennae. One stemma (st) present and close to antenna. Dorsal setae: des1‾3 and des5 elongate; des4 and des6 minute. des1 and des2 located near to middle part of epicranium; des3 and des4 close to frontal suture, or within it; des5 anterolaterally; des6 near to side of epicranium ( Fig. 10 ). Frontal setae: fs1 and fs3 minute; fs2 absent; fs4 long, located anterolaterally; fs5 long, located laterally, close to border of frons ( Fig. 10 ). Lateral setae: les1 very short, les2 as long as des5 . Vertical seta ( ves ) very short. Epicranial area with 4 postepicranial setae ( pes1-4 ) and 3 pores. Antenna with a membranous and slightly convex basal article bearing one arrow-like sensorium; basal membranous article with 7 sensilla of different types: 2 apullacea (sa), 3 styloconium (ss), and 2 basiconium (sb) ( Fig. 11 ). Mouthparts. Clypeus ( Fig. 12 a) 3.3 times wider than long with 2 very short posterolateral cls , and 1 sensillum ( clss ) between the cls ; anterior margin of clypeus curved. Labrum ( Figs 12 āc) 1.7 times wider than long, with 3 pairs of piliform lms1‾3 ; lms1 and lms2 with similar length and distinctly exceeds anterior margin of labrum, lms3 very short. Anterior margin of labrum double sinuate. Epipharynx ( Figs 12 b, c) with 3 finger-like als1‾3 , a pair of pilifrom and relatively elongated ams , 2 relatively short and finger-like mes1‾2 , a pair of sensory pores (snp) outside of labral rods, and a pair of epipharyngeal sensillum clusters (esc). Labral rods (lr) elongate, slightly converging posteriorly, apical part more sclerotized, and basal part slightly enlarged. Mandible ( Fig. 13 ) distinctly broad, bifid, with curved teeth of subequal height; mds piliform, mds2 two times longer than mds1 and located laterally. Maxillae ( Figs 14 ̄16); stipes with 1 stps , 2 pfs , and 1 mbs , with one sensillum (sn) close to mbs ; stps and pfs1–2 relatively long, mbs short; mala with 7 dms1‾7, all dms piliform, almost equal in length; 3 medium to short vms1‾3 ; vms distinctly shorter than dms ( Figs 15 a, b). Maxillary palpi with two palpomeres: I with 1 short mxps and two sensilla; length ratio of I and II: 1:0.7; II with one sensillum and a group of conical, cuticular apical processes. Prelabium ( Fig. 16 ) heart-shaped, with 1 relatively long prms ; ligula with sinuate margin and 2 short ligs1-2 ; premental sclerite well visible, Q-shaped, with distinctly elongated basal parts; labial palpi one segmented, palpomere with one sensillum and short, cuticular apical processes. Postlabium ( Fig. 16 ) with 3 pms1‾3 ; pms1 located medially, and pms2 and pms3 laterally; pms1 very short, almost conical; pms3 medium, and pms2 elongate, distinctly longer than others. FIGURES 4‒9. Anthonomus santacruzi , mature larva, chaetotaxy: 4, 6, 8—thorax and abdominal segment I, 5, 7, 9— abdominal segments V̅X, 4, 5—dorsal, 6, 7—lateral, 8, 9—ventral. Th1–3—pro-, meso- and metathorax, Abd1–9— abdominal segments I̅IX, setae: as —alar, ds— dorsal, eps —epipleural, eus —eusternal, lsts —laterosternal, pda —pedal, pds — postdorsal, prns —pronotal, prs —prodorsal, ps —pleural, sps —spiracular, sts —sternal. FIGURES 10, 11. Anthonomus santacruzi , mature larva: 10—head, 11—antenna. HH—head height, HW—head width, ststemmata, Se—sensorium, sensiliae: sa—apullacea, sb—basiconium, ss—styloconium, setae: des —dorsal epicranial, fs — frontal, les —lateral epicranial, pes —postepicranial, ves —ventral. FIGURES 12, 13. Anthonomus santacruzi , mature larva, mouthparts: 12—clypeus, labrum, and epipharynx (a—dorsal side, b, c—ventral side), 13—left mandible, clss—clypeal sensorium, esc—epipharynx sensillium clusters, lr—labral rods, snpsensory pore, setae: als —anterolateral, ams— anteromedial, cls— clypeal, lms— labral, mds —mandibular, mes— median. FIGURES 14–16. Anthonomus santacruzi , mature larva, mouth parts: 14—maxillolabial complex, ventral, 15a, b—left maxillia and part of praelabium (a—dorsal side, b—ventral side), 16—maxillae and prelabium, sn—sensillium, setae: dmsdorsal malar, ligs— ligular, mbs —malar basiventral, mxps— maxillary palps, pfs— palpiferal, prms— prelabial, pms— postlabial, stps— stipal, vms— ventral malar. Description of pupae Measurements (in mm). Body length 3.10–4.50; widest part (at the level of the middle legs) 1.30–2.50 (see Table 1 ). Colouration. Body white or light yellow. Cuticle smooth. Body shape ( Figs 3 , 17–19 ). Body moderately elongate and rather slender. Rostrum very long (5 times longer than wide). Antennae relatively long and slender. Pronotum 1.7 times wider than long. Mesonotum almost as long as metanotum. Abdominal segments ĪVII of equal length; VIII narrow, IX distinctly smaller than others. Urogomphus elongate; straight; with sclerotized apex. Male and female rostrum of similar length. The shape of the gonothecae is typical for weevil pupae: divided in females ( Fig. 23 a), undivided in males ( Fig. 23 b). Chaetotaxy ( Figs 20 ̄23). Setae yellow to dark brown; very long to minute; hair-like, slightly curved. Long setae located on conical protuberances; medium and minute setae without protuberances. Head capsule ( Figs 20, 21 ) with 1 vs , 1 os , and 1 pas . Rostrum with 2 pairs of rs; rs1 medium, rs2 short. pas as long as rs2 . Pronotum ( Figs 20, 21 ) with 2 as1‾2 , 1 sls , 2 ds1‾2 , and 3 pls1‾3 . Meso- and metanotum ( Fig. 22 ) with 3 long setae placed medially. Femoral setae ( fes ) absent. Abdominal tergites ĪVIII with 3 very long setae ( d1‾3 ) and a single lateral seta ( l ). All abdominal setae located on small conical protuberances. Abdomianl sternites ĪVIII without setae. Abdominal segment IX with 3 pairs of dorsal setae ( d ); urogomphus with 2 pairs of ventral setae ( v ). Addendum to key to pupae of selected Anthonomus species presented by Burke (1968) The species A . monostigma (described by Chacón-Madrigal et al. 2012 ), A . vis (by Bená & Vanin 2013 ), and A . santacruzi (described in the present work) are herein added to the key of Burke (1968) . (previous steps as in Burke’s [1968] original key) 9. Pronotal setae long and very slender...................................................................... 9a - Pronotal setae short and stout...........................................................................9b 9a. Urogomphus forked at apex................................................... Pseudoanthonomus validus Dietz - Urogomphus peaked at apex................................................... Anthonomus santacruzi Hustache 9b. Three pairs of basirostral ( pas ) setae present; urogomphus with slightly bifurcate apex...... Anthonomus albopilosus Dietz - Basirostral ( pas ) setae absent; urogomphus with strongly bifurcate apex...................... A. monostigma Champion (next steps as in original key) 27. sos present; rs absent......................................................................... A. tenuis Fall - sos absent; two pairs of rs present............................................................... A. vis Clark Discussion Pupae of A . vis (described by Bená & Vanin 2013 ) are similar to those of A . cycliferus Fall, 1913 , and the larvae of both species are inquilines in galls ( Burke 1968 ). Chacón-Madrigal et al. (2012) remarked that despite the broad range of plant associations seen among Anthonomini, most known Anthonomus are monophagous species, and host preferences of the larvae are always more restricted than those observed for adults. It is worth stressing that weevil species regarded as polyphagous often establish strictly monophagous local populations even though other potential host plants were reachable (Gosik 2009). FIGURES 17‒19. Anthonomus santacruzi , pupa: 17—ventral, 18—dorsal view, 19—lateral, Th1–3—pro-, meso- and metathorax, Abd1–9—abdominal segments I̅IX, ur—urgomphus. FIGURES 20‒23. Anthonomus santacruzi , pupa: 20, 21—head and pronotum (20—ventral, 21—lateral), 22—dorsal chaetotaxy, 23a, b—terminalia, ventral (a—female, b—male), ur—urogomphus, setae: as —apical, d —dorsal, ds —discal, l — lateral, os —orbital, pas —postantennal, pls —posterolateral, rs —rostral, sls —superlateral, vs— vertical. FIGURES 24‒27. Field photos of Anthonomus santacruzi and Solanum mauritianum : 24— A . santacruzi on S . mauritianum inflorescence, 25, 26— S . mauritianum inflorescences exhibiting A . santacruzi damaged (brown) buds, 27— S . mauritianum with inflorescences in the field. On the other hand, food preferences of adult weevils examined in the laboratory can be quite surprising, e.g., Bagous binodulus Herbst 1795 is regarded as monophagous on Stratiotes aloides L. but preferred Trifolium repens L. and Plantago major L. under laboratory conditions ( Dieckmann 1964 ). The number of larval instars and the average length of head capsules estimated by Chacón-Madrigal et al. (2012) on A . monostigma larvae were similar to those observed on A . santacruzi . The total number of three larval instars (three) and the head widths of mature larvae (~0.50 mm) corresponded with the results of our observations. Also, the setal index of both the larvae and the pupae of A . santacruzi agree with those given by May (1993 , 1994 ) as typical for Curculionidae immatures, and to previously described Anthonomus species as well ( Loicáno et al. 2004 ; Chacón-Madrigal et al. 2012 ; Bená & Vanin 2013 ). Based on larval characters of previously described Anthonomus species, A. santacruzi is close to A. rubicosus (especially with respect to head width, length of fs1 and fs3 , the one-segmented labial palpus, and length of pms ). Remarks on the development of Anthonomus santacruzi Field observations showed that A . santacruzi has a high fecundity, short generation time, and overlapping generations that facilitate rapid population increases. Similar facts were noted by Olckers (2003) , who did the initial biological studies of this weevil. The destructive nature of the larval feeding (within flower buds: Figs 24 ̄27) prevents fruit set, and can thus reduce S . mauritianum ’s extensive seed production ( Florentine et al. 2003 ; Olckers 2003 ; Witkowski & Garner 2008 ). The knowledge about an insects biology is fundamental not only for their protection ( Trnka et al. 2015 ; Shuhrovec & Bogusch 2016 ) but also for their use in biological control of weeds ( Gosik & Skuhrovec 2011 ; Münzbergová & Skuhrovec 2013 ). Potential uses of an insect as a control agent depends on its larval biology ( Skuhrovec et al. 2008 ; Stejskal et al. 2014 ; Abela-Hofbauerova et al. 2011 ; Münzbergová et al. 2015 ). Effective control agents should cause a reduction in the shoot biomass of infected plants or else inhibit their generative abilities. Hence weevil species with larvae that feed on roots or that develop on flower buds are the most effective control agents ( Rowe & Kok 1985 ; Steinger & Müller-Schärer 1992 ; Corn et al. 2006 ; Koprdova et al. 2015 ). On the other hand, species with larvae that feed on leaves (for example) usually only cause minor damage to plants ( Stejskal et al. 2014 ). Moreover, weevils living ectophytically are relatively more vulnerable to predators ( Skuhrovec et al. 2017 ) and thus less effective as control agents. Moreover, some species (potential biocontrol agents) are in fact less effective control agents because of their high rates of infestation by parasites and parasitoids ( Koprdova & Skuhrovec 2007 ). However, parasites or parasitoids of the immature stages of A . santacruzi were rarely observed. Less than 5% of A . santacruzi larvae collected during our observations were associated with immatures of an unidentified parasitoid wasp Pteromalidae (Hymenoptera) . Hence, A . santacruzi appears to be a good example of a species that is well adapted to the role of a biocontrol agent.