Microvelia pulchella Westwood, 1834

Microvelia pulchella Westwood, 1834 View in CoL

is the type species of the genus and one of the most common throughout the American continents, ranging from Canada to Argentina ( Drake & Harris 1928; Drake & Plaumann 1955; Scudder 2008; Mazzucconi et al. 2022). It lives on small pools or on still areas of larger water bodies, with or without hydrophytes or marginal vegetation. They can quickly colonize temporary pools formed after rains and can be found in artificial habitats, such as swimming pools and water fountains (CCR, FFFM pers. obs.). This species has potential as a biological control agent that preys upon mosquito larvae or rice pests, and also can be used as a model for behavioral and ecological studies ( Frick 1949; Miura & Takahashi 1988; Albino-Bohórquez et al. 2024). Its life cycle was first studied in the Nearctic Region by Torre-Bueno (1917) and Hoffmann (1925) and then in more detail by Taylor & McPherson (1999). In the Neotropics, life history traits of this species were studied by Frick (1949) and Albino-Bohórquez et al. (2024), but there still are no detailed descriptions of the immature stages.

The present study provides the first detailed descriptions of the immature stages of M. pulchella based on a population from southeastern Brazil.

Egg

( Fig. 1 View FIGURE 1 )

Oval, covered by waxy cuticle ( Figs. 1A, 1C View FIGURE 1 ). Chorion entirely covered by circular projections of slightly different sizes ( Figs. 1A–C View FIGURE 1 ), more conspicuous where there is no contact with the substratum; micropylar region devoid of projections ( Fig. 1D View FIGURE 1 ). Single micropyle positioned at anterior pole ( Fig. 1D View FIGURE 1 ).

First instar

( Figs. 2A, B View FIGURE 2 ; 3A, B View FIGURE 3 ; 5 View FIGURE 5 ; Table 1 View TABLE 1 )

Comparative morphological measurements of the four instars are presented in Figure 5 View FIGURE 5 as box and whisker plots.

General color brown, darker on dorsum of head and sides of thorax ( Fig. 2A, B View FIGURE 2 ). Eyes red.Antennal interarticular regions, apices of leg segments and abdominal laterotergites translucid. Body densely covered with dark setae more or less organized in rows; rows more evident on abdominal laterotergites. Visible under SEM: dorsal meso- and metathoracic spiracles ( Fig. 3A View FIGURE 3 ), cuticular rugosity on abdominal laterotergites ( Fig. 3B View FIGURE 3 ), transverse rows of microtrichia on abdominal mediotergites (more numerous on posterior segments; Fig. 3B View FIGURE 3 ).

Head short, slightly narrower than pronotum, declivent anteriorly; ecdysial suture conspicuous, ocher, approximately Y-shaped, with frontal sutures curving anteriorly to eyes, mid-dorsal suture continuing onto dorsum of thorax and abdomen. Clypeus projected anteriorly, rounded. Antenniferous tubercle well-developed, rounded. Antenna covered with rows of dark setae; antennomeres I–III cylindrical; II at middle wider than I and III; III shortest; IV fusiform, three times as long as I. Labium dark-brown, shiny, wider on middle of article III, reaching base of forecoxa.

Thorax with pronotum short, wide, detached from mesonotum laterally; posterior margin slightly convex. Mesonotum long, wide; suture with metanotum obscured. Metanotum short, subrectangular; posterior margin shallowly convex. Limits between thoracic and abdominal sterna poorly defined, except for prosternum and mesosternum. Acetabula small; posterior margins rounded. Legs covered with fine dark setae, more densely on anterior surfaces of segments; tibiae also with subapical tuft of setae on posterior surfaces. Femora cylindrical, with similar width. Foretibia narrow at base, thickened towards apex. Foretarsus wide at base, slightly shorter than respective tibia. Middle and hind tibiae and tarsi cylindrical.

Abdomen wide, declivent posteriorly; limits between mediotergites clear, obscured between laterotergites. Pygidium dark-brown, oblique in relation to rest of abdomen.

Second instar

( Figs. 2C, D View FIGURE 2 ; 3C, D View FIGURE 3 ; 5 View FIGURE 5 ; Table 1 View TABLE 1 )

Similar to first instar, except for the following. General color lighter-brown, with darker areas on most of head, pronotum, sides of mesonotum, metanotum, and abdominal mediotergites ( Fig. 2C, D View FIGURE 2 ). Ecdysial suture, intersegmental areas, abdominal laterotergites, and entire venter yellow. Antennomere I mostly pale; apex and rest of antenna gray, except translucid interarticular regions. Coxae, trochanters, tibiae, and tarsi gray. Forefemur pale, except gray apex; middle and hind femora pale at base, remainder gray. Ecdysial suture less evident on dorsum of head. Antenniferous tubercle less-developed. Labium reaching foretrochanter. Tuft of setae on apex of tibiae less evident. Limits between abdominal sterna III–VII clearer. Pygidium lying in a more horizontal position in relation to rest of abdomen.

Third instar

( Figs. 2E, F View FIGURE 2 ; 5 View FIGURE 5 ; Table 1 View TABLE 1 )

Similar to second instar, except for the following. General color darker brown, similar to first instar, with darker areas on vertex, frons, clypeus, pronotum, sides of mesonotum, metanotum, and abdominal mediotergites ( Fig. 2E, F View FIGURE 2 ). Pro-, meso-, and metasterna orangish-brown. Abdominal sterna brown centrally, yellowish laterally. Most of antennomere I and interarticular pieces light-yellow; apex of I and rest of antenna brown; II and IV darker. Labium dark-brown, shiny. Coxae, trochanters, tibiae, and tarsi dark-brown. Forefemur light-yellow, except for narrow brown ring at apex; middle and hind femora light-yellow from base to middle or slightly after middle, remainder brown. Pygidium dark-brown. Antenniferous tubercle indistinct. Labium reaching forecoxa. Femora and tibiae with small subapical tuft of setae on posterior surfaces. Limits between thoracic sterna obscured; clear between all abdominal sterna.

Fourth instar

( Figs. 4 View FIGURE 4 , 5 View FIGURE 5 , Table 1 View TABLE 1 )

Similar to third instar, except for the following. General color light brownish–yellow, with darker brown areas on anterior margin of clypeus, narrow midline on head dorsum, anterior margin and posterolateral angles of pronotum, sides of metanotum and abdominal mediotergites, prosternum, and abdominal sterna ( Fig. 4 View FIGURE 4 ). Yellow ecdysial suture almost imperceptible on dorsum of head, except at base; weak, although visible, on pronotum and abdominal mediotergites I–IV. Coxae and trochanters lighter; hind tibia with central yellow mark. Abdominal spiracles marked by rounded light-brown maculae, more evident throughout development. Labium thinner, elongated, darker at apex, reaching foretrochanters. Pronotum not detached from mesonotum; sutures between meso- and metanota, metanotum and abdominal segment II, and between abdominal laterotergites more developed. Foretibia wider at apex but not markedly dilated. Femora with subapical tuft of setae on posterior surface very discreet. Alary and sexual dimorphism developed. Pronotum of future macropterous individuals prolonged over mesonotum, robust ( Fig. 4E View FIGURE 4 ). Wing buds of future macropterous individuals well-developed, brown, reaching abdominal segment VI, exposing median portions of mediotergites and lateral portions of laterotergites. Abdominal sternum VIII of future female individuals with pair of posterolateral brown marks, divided medially.