Gymnetis merops, Ratcliffe, 2018

Mendoza, Alfredo E. Giraldo, Cobián, Clorinda Vergara & Ratcliffe, Brett C., 2024, Description of the Immature Stages of Gymnetis merops Ratcliffe (Coleoptera: Scarabaeidae: Cetoniinae: Gymnetini), The Coleopterists Bulletin 78 (1), pp. 99-107 : 100-105

GYMNETIS MEROPS Ratcliffe , third instar and pupa ( Figs. 2C–I , 3 )

Material Examined. PERU. Ica: Ica, vineyard, xi.2012, 5 larvae ( MEKRB) , Los Aquijes , vineyard, 10.vi.2013, 4 second-instars ( MEKRB) , 1 third-instar ( MEKRB), Santiago , La Venta, vineyard, 17.x.2018, 6 larvae ( MEKRB) . Lambayeque: Chiclayo, Zaña , guinea pig manure, 17.viii.2013, 2 third-instars ( MEKRB) , 4 pupae ( MEKRB) , 25.xi.2013, 2 second-instars ( MEKRB) , 2 third-instars ( MEKRB), 1 pupa ( MEKRB) . Lima: Lima, La Molina , urban garden, 05.ix.2022, C.Huaripata, 15 larvae ( MEKRB) , 6 pupae ( MEKRB) , Los Olivos , 11.94230S 77.07177W, urban garden, 03.xii.2021, A. Giraldo, 1♂ adult ( MEKRB) , 08.iv.2022, A. Giraldo, 1♂ adult ( MEKRB) , 11 third-instars ( MEKRB), 03.v.2022, A. Giraldo, 7 third-instars ( MEKRB) , 06.viii.2023, A. Giraldo, 4 third-instars ( UNSM) .

Description of Third Instar ( Figs. 2C, D , 3A–J ): Body length 29.24–37.72 mm, mean = 33.14 mm, n = 9 ( Fig. 2B ). Head ( Fig. 3A ): Maximum width of head capsule 4.0– 4.3 mm. Cranium: Smooth, color yellowish brown. Frons with median longitudinal depression, a single posterior frontal seta, without anterior frontal and external setae, and a single anterior angle seta. Dorsoepicranium with 1 large and 6–8 small setae in a line diverging from mediobasal portion of head and 1 lateral line of 6 short setae on each side. Tentorial pits lacking. Stemmata absent. Clypeus: Shape subtrapezoidal with 2 posterior clypeal setae and 2 exterior clypeal setae at each side. Preclypeus weakly sclerotized and without setae. Labrum:Anterior border trilobed, clithra present. Antenna: First antennomere shorter than the 2 following antennomeres together. Last antennomere with 2 dorsal, 1 ventral, and 3 apical sensory spots ( Figs. 3B, C ). Epipharynx ( Fig. 3D ): Plegmata absent. Corypha with 8 long, stout setae. Haptomeral region with a curved row of 10–12 heli and 8–10 stout, spine-like setae irregularly placed behind row. Acanthoparia with 7–8 short setae. Chaetoparia with 30–34 setae on each side. Dexiotorma long, laetorma short, and pternotorma small and rounded. Nesia with sensorial cone. Haptolachus without sensillae below the cone. Mandibles: Right mandible ( Fig. 3E ) with 1 scissorial tooth anterior to scissorial notch and 2 weakly defined scissorial teeth posterior to notch. Stridulatory area elongate, length over 3 times its width. Molar area trilobed, lateral edge with 7 setae, dorsal surface on apical half with 2 setae. Brustia formed by 5 setae. Left mandible ( Fig. 3F ) with 1 scissorial tooth anterior to scissorial notch and 2 well-defined scissorial teeth posterior to notch. Molar area trilobed, lateral edge with 5 setae, dorsal surface on apical half with 2 setae. Basomedian angle with brustia consisting of 6 setae. Maxilla ( Fig. 3G ): Mala with large uncus at apex and 1 subterminal, bifid uncus. Stridulatory area with row of 3–4 curved, acute teeth and a distal, blunt process. Labium ( Fig. 3G ): Hypopharyngeal sclerome asymmetrical, left side with 6–7 setae, right side more prominent, sclerotized except for a basal, unsclerotized, circular area without setae. Thorax: Thoracic spiracles with C-shaped respiratory plate, size 1.0 mm high and 0.66 mm wide. Dorsal area of thoracic segments with abundant setae. Legs: Tarsungulus cylindrical ( Fig. 3H ), rounded apically, possessing 9–11 setae. Abdomen: Spiracles of abdominal segments I–VIII similar in size, distance between the 2 lobes of the spiracle respiratory plates less than the dorsoventral diameter of the bulla ( Fig. 3I ). Dorsal surface of segments I–X with abundant long and short setae irregularly placed, longer posteriorly. Dorsum of segment VII with 2 annulets. Segments IX and X fused, covered with short and long setae. Spiracular area of abdominal segments I–VIII with 42–55 setae. Raster ( Figs. 2D , 3J ): Palidia monostichous, opened posteriorly and closed anteriorly, each palidium consisting of a row of 19–23 spiniform pali. Septula elongate, length around 10 times its width. Lower anal lip with many short and medium size setae prox- imally to the anal aperture and many long setae distally.

Description of Pupa ( Figs. 2E–I ): Body length 20.87–24.16 mm, mean = 22.52 mm, n = 12. Shape subovate, stout, exarate. Color light testaceous. Entire body with very fine, velvety microtrichia. Head: Glabrous, bent downward, mouthparts sep- arated.Clypeus trapezoidal,slightly concave.Antenna, labrum, mandibles, maxillae and palps discernible; antennal tecae expanded, stout, with rounded apices. Compound eyes sunken, partially covered by anterior edges of pronotum. Thorax: Pronotum glabrous, convex, with defined margins, subheptagonal, widest posteriorly, with 2 rounded protuberances adjacent to the pteroteca, basal margin slightly bis- inuate, center of base projecting posteriorly as in adult.A narrow, median, longitudinal sulcus extend- ing from apex to near base. Meso- and metascutella acute, projecting posteriorly. Thoracic spiracle present in cavity formed by anterior and middle legs, hypomeron, and pterothecae. Pteroteca free, com- pressed around body, hind wing teca longer, reach- ing abdominal sternite IV. Mesometasternal process with rounded apex emerging between pro- and me- socoxae. Metasternum wider than long. Protibia with 3 well-defined protuberances and 1 apical spur. Meso- and metatibiae with 2 apical spurs. Legs: Protibia with 3 short teeth on external apical border and tuberculiform apical spurs. Meso- and metatibiae each with 2 well-developed inner spurs. Metafemur covered by pterotheca. Tarsomeres and pretarsus distinct; protibial pretarsi at level of me- sofemur, mesotibial pretarsi at level of metafemur, metatibial pretarsi at level of abdominal sternite VIII. Abdomen: Tergites II–VI with tergo-lateral surface rugose, segment VII vaguely or devoid of rugosities. Dioneiform organs absent. Spiracle I ovate with sclerotized peritreme covered by the hind wing pteroteca and protected by a fleshy fold. Spiracles II–IV ovate, prominent. Spiracles V–VIII closed. Female pupa ( Fig. 2H ) with genital ampulla convex and wide on surface of sternite IX. Male pupa ( Fig. 2I ) with genital ampulla formed by 2 large, semicircular lobes on surface of sternite IX.

Distribution and Natural History. According to label data of specimens examined at MEKRB, MUSM, SENASA, UNASAM, and UNPRG, and published records by Ratcliffe (2018), Di Iorio (2014), and Juárez-Noé and González-Coronado (2018, 2019), G. merops is widely distributed in dry forest and coastal desert ecoregions to the Peruvian Andes from Piura to Ica (5°– 14°S) and also recorded in some localities from interandean valleys, mon- tane forest, and tropical rainforest ecoregions east of the Andes ( Fig. 4 ). Interestingly, many records of this species are located in anthropogenic envi- ronments, such as urban green areas and agricultural valleys as verified by our field observations.Adults of G. merops have been observed feeding on a va- riety of sugar-rich food sources, such as apples (Tejada and Morón 2015), bananas (Gonzáles and Cabrera 2015), grapes ( Deza 2019; Gonzales and Cabrera 2017; Narrea-Cango et al. 2013), honey (Tejada and Morón 2015), mangos (Gonzáles and Cabrera 2017), prickly pears (Juárez-Noé and González-Coronado 2019), and sunflowers (Gonzáles and Cabrera 2015). The larvae are capa- ble of developing in well-drained soils, under accu- mulations of uncomposted organic matter or decomposing foliage that are usually found in cul- tivated fields and urban gardens (Tejada and Morón 2015 and our field observations). It is considered a pest species in vineyards due to the significant dam- age caused by adults feeding on buds and mature fruits, and larvae, which eat roots ( Narrea-Cango et al. 2013 and label data cited by Ratcliffe 2018). In these scenarios, methods used for population control include foliage pruning, insecticide applica- tion, hand collecting of larvae, and adult capture with fruit-baited traps ( Deza 2019), as well as assays with entomopathogenic nematodes ( Narrea-Cango et al. 2013) and toxic plant exudates (Gonzáles and Cabrera 2017).

The life cycle of G. merops was studied under laboratory conditions in Trujillo (20 °C, 93% RH) (Gonzáles and Cabrera 2015) and Ica (21.7 °C, 68.7% RH) ( Deza 2019).According to these studies, the duration of egg, larval, and pupa stages were approximately 14, 195, and 45 days, respectively.

In most studies conducted in Peru, specimens of G. merops remained unidentified or were errone- ously assigned to other superficially similar species such as Gymnetis balzarica Janson, 1880 (Juárez-Noé and González-Coronado 2018), Gymnetis bonplandii Schaum, 1844 (Gonzáles and Cabrera 2015), or Gymnetis chevrolati Gory and Percheron, 1833 and G. pudibunda (Tejada and Morón 2015) . After revision of the genus Gymnetis ( Ratcliffe 2018) , adult specimens of G. merops can be reliably distinguished from these species based on available geographic distribution and morphological diagno- ses. Following the original description ( Ratcliffe 2018), G. merops adults are characterized by a combination of pronotum velutinous black with pale yellow lines; mesometaventral process relatively slender, projecting forward and slightly downwards from ventral axis of body; elytra velutinous black with extensive, irregular pattern of pale yellow; and lateral marginal bead shiny yellow.

Figures

Fig. 2. Gymnetis merops. Adult: A) Holotype from La Libertad, Viru (UNSM), B) Specimen from Lima, Los Olivos (MEKRB). Third instar larva: C) Lateral view, D) Last abdominal segments. Female pupa: E) Dorsal view, F) Lateral view, G) Ventral view, H) Ventral view of apex with genital ampulla. Male pupa: I) Ventral view of apex with genital ampulla. Scale bars: A–C, E–G = 5 mm; D = 1 mm; H, I = 2.5 mm.

Fig. 3. Gymnetis merops, third instar larva.A) Head, frontal view, B) Last antennomere, dorsal view, C) Last anten- nomere, ventral view, D) Epipharynx, E) Right mandible, ventral view, F) Left mandible, ventral view, G) Hypopharynx and left maxilla, ventral view, H) Tarsungulus of posterior leg, I) Abdominal spiracle, J) Raster. Scale bars: A = 1 mm; B–J = 0.5 mm.

Fig. 4. Distribution map of Gymnetis merops.