Translator Disclaimer
1 June 2015 External Morphology of the Immature Stages of Vatiga manihotae (Hemiptera: Tingidae) with Comments on Ontogenesis
Ana Paula Gonçalves Da Silva Wengrat, Viviana Cauduro Matesco, Kim Ribeiro Barão, Jocelia Grazia, Vanda Pietrowski
Author Affiliations +
Abstract

Vatiga (Hemiptera: Tingidae) species show preference for Cassava plants (Euphorbiaceae: Manihot), an important food source in the American tropics. Infestations of Cassava by Vatiga can cause serious harvest losses. Information on immature stages morphology can aid in early identifications of crop pests and provide data for use in phylogenetic analyses; thus, we describe and illustrate the external morphology of all life stages of Vatiga manihotae using optical and scanning electron microscopies. Eggs are laid inserted in the leaf blade, are whitish and oblong, with smooth chorion. In the larvae, the tegument is covered by hemispherical projections, which remain the same and become denser through ontogenesis. Dorsal surface of head and lateral margins of body with tubercles; from the second through the fifth instars the cephalic and lateral tubercles maintain the same structure, only adding setae along its surfaces. The cephalic tubercles of V. manihotae nymphs are more complex than those of the adults, as on the latter the cephalic tubercles lack setae. As suggested by literature, our discoveries fit the intermediate clades scenario of the ontogenetic pathway in which larvae have outgrowths and adults are simple, suggesting that brood protection is absent and larval protection by secretions may be present.

Tingidae (Hemiptera: Heteroptera: Cimicomorpha) includes about 2,600 species, which in part are easily recognized by their lacy pronotum, scutellum, and hemelytra (Guilbert 2001). The taxonomy of the family is based mostly on external morphological structures (Guilbert 2004a), and adults and nymphs may show strikingly elaborated tegumental ornamentations (Guilbert 2001, 2004b).

Tingid nymphs already have been considered in the systematics of the family (Guilbert 2001), but the knowledge of nymph morphology still is poor. Most nymphal descriptions focus only on the fifth instar (Guilbert & Montemayor 2010; Montemayor 2010; Montemayor et al. 2011; Guidoti & Montemayor 2014), and few provide descriptions of all instars (e.g., Livingstone 1976; Montemayor 2009; Montemayor & Dellapé 2010; Guidoti & Barcellos 2013). Fewer papers focus on immature stages of Neotropical species (e.g., Montemayor 2009; Guilbert & Montemayor 2010).

The taxonomic and systematic knowledge on the Neotropical Vatiga Drake & Hambleton is limited. Froeschner (1993) revised the genus, proposed new synonymies, and established the current genus composition: Vatiga cassiae (Drake & Hambleton), V. illudens (Drake), V. manihotae (Drake), V. pauxillae (Drake & Poor), and V. varianta (Drake). Information on the morphology of Vatiga species is scattered in the literature and mostly is restricted to the species` original descriptions; also, the immature stages still are unknown.

Vatiga species show preference for Manihot Miller (Euphorbiaceae) plants, commonly known as “cassava”. Cassava plants are an important food source in the American tropics, and infestations by Vatiga, especially V. manihotae, can cause serious harvest losses (Bellotti et al. 1999).

The aim of this article is to describe and illustrate all immature stages of V. manihotae, as a help to identify early developmental stages of V. manihotae and to provide morphological data on Vatiga immatures for future use in phylogenetic analysis.

Material and Methods

Adult and immature specimens of V. manihotae were collected manually on leaves of Manihot esculenta Crantz (Euphorbiaceae), in the Brazilian states of Bahia, Mato Grosso do Sul, Paraná, and Santa Catarina, from 2009 to 2013. Eggs were obtained by dissecting fresh leaves. Specimens were preserved in 70% ethanol.

The adults were identified to species level based on Froeschner (1993). Drawings were made with a camera lucida coupled to a stereomicroscope, digitalized, and edited with a vectorial image processor. For observation of the dorsal abdominal scent glands, nymphs were cleared in 10% KOH and stained with Congo Red.

In addition, all stages were observed by scanning electron microscopy (SEM) at the Centro de Microscopia Eletrônica (CME) of UFRGS. For SEM analysis, specimens were kept submersed in contact lens solution for 24 h, then washed three times in distilled water, and dehydrated in increasing concentrations of acetone. Samples were dried further in a critical point dryer, mounted on stubs, metalized with carbon and gold in a Baltec SCD050 sputter coater, and analyzed with a JSM6060 scanning electron microscope.

Measurements (mean ± standard deviation; 15 nymphs of each instar), given in millimeters, include: total length (TTL), from head apex to abdomen apex, along longitudinal mid-line, not including the antero-median tubercle; total width (TTW), corresponding to the largest abdominal width (at posterior margin of the urosternite V, not including the lateral tubercle); head length (HL), along longitudinal mid-line, not including the antero-median tubercle; head width (HW), at mid-level of eyes; interocular distance (ID), at mid-level of eyes; length of antennal segments I, II, III, and IV; rostrum length (RL); thorax length (TL), along longitudinal mid-line; thorax width (TW), at pronotum not including the tubercles; and wing pad length (WL), from 3rd to 5th instars, corresponding to the greatest length, at a paramedian line (Table 1).

Table 1.

Morphometric parameters (mean ± standard deviation), in millimiters, of the Vatiga manihotae nymphs (n = 15, for each instar).

t01_620.gif

Terminology follows Southwood (1956) and Baker & Brown (1994) for eggs, and Guilbert (2005) and Guidoti & Barcellos (2013) for nymphs. Voucher specimens are deposited in the Coleção Entomológica of Departamento de Zoologia of Universidade Federal do Rio Grande do Sul and in the Laborató