Cecidonius pampeanus Moreira & Goncalves

Moreira, Gilson R. P., Eltz, Rodrigo P., Pase, Ramoim B., Silva, Gabriela T., Bordignon, Sergio A. L., Mey, Wolfram & Goncalves, Gislene L., 2017, Cecidoniuspampeanus, gen. et sp. n.: an overlooked and rare, new gall-inducing micromoth associated with Schinus in southern Brazil (Lepidoptera, Cecidosidae), ZooKeys 695, pp. 37-74 : 42-51

Cecidonius pampeanus Moreira & Goncalves sp. n. Figs 2, 3, 4, 5, 6, 7, 8, 9

Diagnosis.

As discussed for the monotypic genus.

Description of adults.

As described for the monotypic genus.

Type material.

Brazil: Old grass field, private farm belonging to Antonio Malta, Coxilha das Lombas, 30°01'46"S, 50°36'40"W, 86m, Santo Antônio da Patrulha Municipality, Rio Grande do Sul State (RS), Brazil; G.R.P. Moreira, H. A.Vargas, R. Brito & S.A.L. Bordignon; 29.V.2012, pinned-dry preserved adults, reared by the first author from dehiscent galls collected on the ground around patches of Schinus weinmannifolius Mart. ex Engl. plants. Holotype ♂: LMCI 188-4, emerged on 9.XI.2012; donated to DZUP (33.342). Paratypes: 1♂ (LMCI 188-7), emerged on 21.XI.2012, donated to DZUP (33.352); 1♀ (LMCI 188-6), with genitalia on slide (GRPM 50-127), emerged on 19.XI.2012, donated to DZUP (33.362).

Additional specimens used for morphological descriptions, with the same collection data as the type material: 1♂ (LMCI 188-5), emerged on 18.XI.2012, mounted on three slides in Canada balsam, genitalia (GRPM 50-124), head and thorax (GRPM 50-125) and wings (GRPM 50-126); three pupae (LMCI 188-8), three last instar larvae (LMCI 188-11), and several galls, dissected from galls induced on S. weinmannifolius plants, fixed in Dietrich’ fluid and preserved in 70% ethanol; two last instar larvae, mounted similarly on slides (GRPM 50-128 and 129).

Etymology.

The epithet refers to Pampa, a biogeographic province within the Chacoan subregion (sensu Morrone 2006), predominantly composed of grasslands, and where C. pampeanus was first found.

Description of immature stages.

Larva (Figs 5, 6, 9D, F): With five larval instars, which can be separated from each other by the head capsule width.

First instar (Fig. 6A, B). Head capsule width (average + standard error) = 0.066+0.009 mm; body length = 0.570+0.058 mm, n = 4. Head yellowish brown, with chewing mouthparts. Stemmata absent; antennae reduced, located close to mandibles; labrum subquadrate, with three pairs of minute setae; mandibles well developed, with four cusps along distal margin; maxilla with palpus and galea poorly developed; spinneret well developed, tubular; labial palpus one-segmented, bearing an apical sensillum. Thorax and abdomen creamy-white, cylindrical and U-shaped, with no developed primary setae; prothoracic shield, thoracic legs, prolegs, and abdominal calli absent.

Second instar (Fig. 9D). Similar in shape and color to fifth instar; head capsule width = 0.160+0.004 mm; body length = 1.060 + 0.134 mm, n = 3.

Third instar. Similar in shape and color to fifth instar; head capsule width = 0.217+0.005 mm; body length = 2.078 + 0.052 mm, n = 3.

Fourth instar. Similar in shape and color to fifth instar; head capsule width = 0.452+0.017 mm; body length = 3.990 + 0.700 mm, n = 4.

Fifth instar (Figs 5, 6 C–L, 9F). Head capsule width = 0.898+0.031 mm; body length = 7.190 + 1.722 mm, n = 5. Head yellowish brown, with anterior margin orange-brown and lateral margin convex; frontoclypeus subtriangular, well-marked by pigmented adfrontal sutures, extending to apex of epicranial notch. Two well-developed, latero-located stemmata; antennae 2-segmented, with five sensilla, four short and one ~5x longer the others; labrum slightly bilobed, with three pairs of setae on distal margin; mandible well developed with four cusps along distal margin and one seta basally on external surface; maxilla with palpus and galea reduced; spinneret tubular to conical; labial palpus one-segmented, with well-developed apical seta. Chaetotaxy consisting of 14 pairs of setae: F group unisetose; C group unisetose; A group trisetose; AF group unisetose; P group bisetose, reduced in length; S group trisetose, one reduced in length; SS group trisetose.

Thorax (T) and abdomen (A) creamy-white, cylindrical, slightly curved, covered with microtrichia. Prothoracic shield light yellowish; thoracic legs and abdominal prolegs absent; abdominal segments A2 to A7 with well-developed calli, located on posterior margin of terga. A10 composed of three lobes, one dorsal and two latero-ventral. Circular spiracles without elevated peritreme, laterally on T1, A1-8. Thoracic segments surrounded by short setae interspersed with long ones (~5x longer). T1 with 12 pairs of setae: D group bisetose; XD unisetose; SD unisetose, outside prothoracic shield; L group trisetose, anterior to spiracle; SV group trisetose; MV unisetose; V unisetose. T2-3 with 10 pairs of setae: D group bisetose; SD bisetose; MSD unisetose; L group bisetose; SV group bisetose; V unisetose.

Abdominal segments (AB) with only short setae that are more or less aligned on the middle region of each segment, which are tentatively named. AB1-7 with 6 pairs of setae: D group bisetose; L group trisetose, posterior to spiracles; V unisetose. AB8 with 8 pairs of setae: D group bisetose; SD group unisetose; L group tetrasetose, posterior to spiracles; V unisetose. AB9 with 5 pairs of setae: D group unisetose; SD group unisetose; L group unisetose; SV unisetose; V unisetose. A10 with six pairs of setae: D group bisetose; SD group unisetose; SV trisetose.

Pupa (Figs 7, 8). Length = 6.44+0.52 mm; n = 3. Yellowish brown, with head, thorax, and abdominal spines becoming dark brown near adult emergence (Fig. 7C). Head with frontal process (gall-cutter) formed by three processes; one large, inverted U-shaped, located in the centre, which is flanked at the base by the other two that are ~5x shorter than the central one, directed laterally and slightly bent to the anterior side (Figs 7, 8A, B). Antennae narrow, long, slightly surpassing forewing apex; prothorax a narrow transverse band between head and mesothorax; hindwings concealed by forewings, reaching posterior margin of sternum A6; pro- and mesothoracic legs extended to A4 and A5, respectively; metathoracic legs reaching beyond forewing apex on segment A7 (Fig. 7). Frons and lateral portion of vertex with two pairs of setae each; tergum T2 with a pair of latero-dorsal setae; tergum T3 with a single seta on each side. Abdominal segments with central region covered by microtrichia; A2-9 with a transverse band of stout spines (Fig. 8E), near anterior margin of terga; tergum A10 with a pair of acute processes on posterior margin (Fig. 8F). Abdominal setae slightly shorter than thoracic, arranged in three rows (dorsal, supra- and subspiracular); one dorsal pair on segments A1-8; one supra-spiracular pair on segments A2-8; four subspiracular pairs on segments A3-6 (Fig. 8D); seven subspiracular pairs on A7-8; six pairs latero-ventrally on A10; spiracles with slightly elevated peritreme, laterally on A2-8, spiracle on A8 partially closed.

Natural history.

The unilocular, club-shaped, green galls of C. pampeanus develop initially enclosed within swollen stems of S. weinmannifolius branches (Fig. 9B, C). Later on in ontogeny, they erupt from the stem surface, either as isolated units or in small groups, and may reach a few tens per branch (Fig. 9F). The larval chamber is almost cylindrical in shape (maximum length = 7.99+0.58 mm; n = 6), and transverse to the stem axis. The external wall is shallow and thinner distally, formed as an expansion of the wood tissue under the bark (Fig. 9 D–F). During the last larval instar, C. pampeanus galls have their wall somewhat annealed and ruptured at the base (Fig. 9G), when they fall freely to the ground containing the larva inside. The basal orifice left on these galls consequently is clogged by feces (Fig. 9I). These are continually deposited, then dry and solidify at the bottom of the gall chamber. After falling, the gall progressively dries up, turning a dark brown color (Fig. 9J). The external part may appear rotted in some old galls, when thin, longitudinally aligned groves are found on the gall surface. Like O. argentinana galls ( Moreira et al. 2012), those of C. pampeanus also lack an operculum. With the action of the frontal process and body contortions, the pupa opens an irregular orifice on the distal, weaker wall (Fig. 9H). By continuing these movements and anchoring the body laterally with its abdominal spines, the pupa pushes itself partially out of the gall. During this process, the anterior portion of the exuviae is split, allowing adult emergence. In all cases of adult emergence followed under laboratory conditions, the anterior part of the pupal exuviae (head and thorax) was found protruding to the outside, while the posterior third remained in the chamber.

Field collections carried out during five consecutive years at the type locality indicated that C. pampeanus is a univoltine species, larvae growing during the summer when young galls are seen on S. weinmannifolius stems. Fully developed galls containing last instar larvae have been collected mainly during autumn. Based on several dissections of galls on the ground that were field collected during the winter, it can be inferred that the species overwinters in the larval stage, pupation occurring in spring, and adults emerging later on. This time of the year coincides with full vegetative activity of S. weinmannifolius host plants, including production of new sprouts. In the populations of S. weinmannifolius located in the study area, several plants can be attacked by C. pampeanus , and many branches within a patch of plants can bear galls induced by them. Under severe attack by C. pampeanus , S. weinmannifolius stems may wilt, die, and then fall, but the underground portion may stay alive. Under low gall densities, however, the aerial portion of plants stay green throughout the year, the signs of detached galls appearing as small, cylindrical craters on their stem surface.

In the populations studied here, C. pampeanus larvae are only common to find in yearly stages, within those galls still under the bark. Free-living larvae are rarely found in the external galls. These are severely attacked by unidentified parasitoids belonging either to Lyrcus Walker ( Pteromalidae ) or to Allorhogas Gahan ( Braconidae ), whose taxonomy and biology will be treated in detail elsewhere. Larvae of Lyrcus are ectopara sitoids found singly attached to C. pampeanus larvae inside the galls (Fig. 10A). They suck the internal contains of larvae, killing them and leaving only their exoskeletons intact. These parasitoids pupate inside C. pampeanus galls (Fig. 10B), which do not have their main shape changed, but turn a dark brown colour. In this case, galls stay attached to the stems for a longer time compared to ones free of parasitoids. After emergence, adults of Lyrcus open a characteristic, small orifice on the distal portion of the gall (Fig. 10C), through which they leave. By contrast, larvae of Allorhogas are gregarious and inquilines. They modify C. pampeanus galls, inducing production of additional tissue. When initially viewed externally in this case, C. pampeanus galls appear partially surrounded by this type of tissue (Fig. 10E). Later in ontogeny they are completely involved by such tissues, turning into globular, pinkish, large galls (up to 3.2 cm in diameter; n = 8) that last much longer in the field and promptly call attention (Fig. 10D, F). These galls are multilocular; larvae of inquilines are found individually in several chambers within (Fig. 10G). Pupation also occurs inside galls, that then dry up and turn dark brown; adults of inquilines leave through small circular orifices that are found on the gall surface (Fig. 10H).

Host-plant and distribution.

Galls of C. pampeanus have been found only on branches of Schinus weinmannifolius Mart. ex Engl. ( Anacardiaceae ). This is a small shrub (up to 50-cm tall), originally found scattered in open savannas (Fig. 9A), hill tops and forest borders of southern South America, including central and south Bra zil, Paraguay, northeast Argentina and Uruguay ( Barkley 1957, Luz 2011). However, populations of S. weinmannifolius bearing galls of C. pampeanus were found only in Rio Grande do Sul, the southernmost state of Brazil, particularly in the surroundings of Porto Alegre city (Fig. 11A) in the eastern limit of the Pampean province within the Chaco biogeographic region (sensu Morrone 2006). This region, also known as the Southeastern Highlands, since it reaches higher elevations than the remaining Pampean areas, includes several low-elevation hills (up to 300 m) that are more or less interwoven with fragments of semi-deciduous forests, herbaceous and shrub vegetation and single-layer grasslands, forming a mosaic. In this area a few, isolated, populations of S. weinmannifolius were found either as isolated plants or forming small patches (up to 3m in diameter), primarily located on hilltops and hill slopes, and a few scattered in the single-layer grasslands that prevail in the lower elevation areas.

Little is known about the biology or natural history of S. weinmannifolius . Although also found as isolated individuals, it usually forms small patches of plants, particularly in sandy soils. Preliminary field observations suggest that S. weinmannifolius is perennial, having a subterraneous habit of growth, forming stolons that grow just below ground and from which new sprouts emerge every year, starting in spring. At the type locality, the first flowers appear during November and the flowering season may last until March; fruits are found on plants from December to May. There is ap parently little if any vegetative growth during the winter, which is also the season when the aerial parts of S. weinmannifolius plants may wilt and die.

Population genetic structure.

Inferences on the genetic variability of C. pampeanus resulted from 42 (3%) variable sites. Overall, haplotype (Hd) and nucleotide diversity (π) were 0.92 ± 0.01 and 0.0007 ± 0.0009, respectively (Table 2). Individual populations presented Hd from 0.33 to 0.73 (P9 and P10, respectively) and π from 0.002 to 0.0013 (P9 and P10, respectively). A total of 14 haplotypes were found in ten populations (Table 2; Fig. 11B). We found only one haplotype in each in P1 to P5; therefore, standard diversity indices and neutrality tests were not performed. From P6 to P9 two haplotypes per site were observed; P10 presented three haplotypes, the highest diversity. Except for H1 and H9, which were shared between P5/P6 and P9/P10 respectively, all were unique to each locality (Fig. 11B). Characterization of pairwise gene flow based on the FST index indicated significantly high levels of genetic structure in populations of C. pampeanus . Overall, FST ranged from 0.55 to 1 (P <0.05) (Table 3). The lowest level observed was 0.20, between P5 and P6, not significant (P> 0.05). Spatial genetic structure assessed by the correlation between genetic and geographic distances indicated a significant pattern of isolation by distance for the ten populations (r = 0.74, P <0.01) (Fig. 11C). Quantitative differentiation based on two groups of comparison reinforced the structure by distance pattern (Suppl. material 2). Both analyses ( Jacuí River as a barrier and geographic distance) found similar values of FST (0.97; P <0.001). However, when we grouped P2 with the cluster formed by P4 to P10 the divergence among groups was lower (46.45%; P <0.001) than when we grouped it with P1 and P3 (58.73%; P <0.001). Similarly, the divergence among populations within groups decreased from the first to the second scenario (51%, P <0.01; 39.15%, P <0.001, respectively).

Finally, analysis of demographic history by mismatch distribution indicated an overall multimodal pattern for C. pampeanus that is not compatible with a scenario of recent demographic expansion (Suppl. material 4). Single population analysis indicated a unimodal pattern, particularly for P9 that showed a possible scenario of expansion. In addition, overall neutrality tests yielded positive and non-significant values for all indices with respect to neutral expectations (Table 2). Single populations presented positive values, except P7 that showed negative values (but non-significant) for some parameters (i.e., Tajima´s D and Fu and Li’s D and F) and P9, that presented all negative (but non-significant) values.