Hymenoptera: Platygastridae: Sceliotrachelinae)
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MORPHOLOGY,HISTOLOGY, AND FINE STRUCTURE Morphology and Development of Immature Stages of Fidiobia dominica (Hymenoptera: Platygastridae: Sceliotrachelinae) 1 2 2 JOSEP-ANTON JACAS, JORGE E. PEN˜ A, AND R. E. DUNCAN Ann. Entomol. Soc. Am. 100(3): 413Ð417 (2007) ABSTRACT The external morphology and development of immature stages of Fidiobia dominica Evans & Pen˜ a (Hymenoptera: Platygastridae), a Neotropical solitary endoparasitoid of the eggs of Diaprepes spp. (Coleoptera: Curculionidae), are reported. This species behaves as a solitary idiobiont endoparasitoid. It has a stalked egg and two instars. The Þrst instar is cyclopoid and seven-segmented, whereas the second instar is hymenopteriform and 11-segmented. Mandibulae are conspicuous in both instars. On completion of the larval development, the host egg turns amber transparent, making parasitized eggs easily recognizable. The pupa is exarate. F. dominica is a protandrous species and once emerged, males help females to emerge. KEY WORDS Diaprepes abbreviatus, biological control, egg parasitoid Fidiobia dominica Evans & Pen˜ a (Hymenoptera: (Clausen 1940, Askew 1971, Masner 1995, Austin et al. Platygastridae) is a solitary egg endoparasitoid that 2005). The genera of this subfamily that parasitize attacks at least two species of root weevils, Diaprepes coleopteran eggs are solitary idiobiont endoparasi- doublerii Gue´rin and Diaprepes abbreviatus (L.) (Co- toids and are thought to develop in a way similar to leoptera: Curculionidae), indigenous to the Carib- that of Scelionidae (Masner 1995). Although the Þrst bean region (Evans and Pen˜ a 2005). D. abbreviatus instar of some platygastrids is more or less hymenop- was introduced into Florida in 1964 (Woodruff 1968) teriform, Þrst instars of many species are extraordinary and since has become a serious pest of citrus through- in appearance and superÞcially resemble cyclopoid out much of central and southern Florida, and it is copepods (Clausen 1940, Askew 1971). When fully currently spreading in the citrus-growing regions of grown, these larvae are extremely bloated and ovoid. Texas and California (Grafton-Cardwell et al. 2004). A The number of instars seems to vary from one to three, lack of native egg parasitoids for this weevil in citrus depending on species (Clausen 1940, Masner 1995, orchards in Florida (Hall et al. 2001), and past failures Sampson et al. 2006). The incomplete knowledge on of classical biological control (Beavers et al. 1980), this important group of natural enemies compelled us have triggered renewed efforts to introduce, release, to study and provide basic information on the external and evaluate candidate egg parasitoids from the Ca- morphology and development of immature stages of F. ribbean region into Florida (Pen˜ a et al. 1998, Pen˜ a and dominica. Amalin 2000, Hall et al. 2002, Jacas et al. 2005, Castillo et al. 2006). One of these candidate species, F. do- Materials and Methods minica, a platygastrid wasp collected in Dominica from D. doublerii egg masses, was subsequently introduced Specimens used in this study were obtained from into Florida in April 2003, and it has been reared a colony initiated from individuals of F. dominica through Ϸ50 generations on D. abbreviatus eggs in the imported from Dominica (Evans and Pen˜ a 2005). quarantine facility in Homestead, FL (Evans and Pen˜ a The colony was maintained on D. abbreviatus eggs 2005). The release of this parasitoid was approved in in the insectary facilities of the University of Florida June 2006, and releases are under way at various sites at the Tropical Research and Education Center in Florida as part of the classical biological control (TREC) at 25.6 Ϯ 1ЊC, Ϸ65% RH, and a photoperiod program against this pest. of 12:12 (L:D) h. Voucher specimens of F. dominica Little is known about the biology and the immature are deposited in the Florida Collection of Arthropods, morphology of Platygastridae and even less so about Gainesville, FL, U.S. National Museum of Natural His- that of species in the subfamily Sceliotrachelinae tory (USNM), and in the Canadian National Collec- tion, Ottawa, Canada. 1 Corresponding author: Universitat Jaume I, Departament de Stock Colonies. Adult D. abbreviatus root weevils Cie`ncies Agra`ries i del Medi Natural, Campus del Riu Sec, E-12071- were collected from the foliage of ornamental trees in Castello´ de la Plana, Spain (e-mail: [email protected]). nurseries around TREC, Homestead, FL (25Њ30 N, 2 Department of Entomology and Nematology, Tropical Research and Education Center, University of Florida, 18905 SW 280th St., 80Њ30, 1-m altitude). The weevils were placed in 30- by Homestead, FL 33031. 30- by 30-cm Plexiglas cages with water and foliage of 0013-8746/07/0413Ð0417$04.00/0 ᭧ 2007 Entomological Society of America 414 ANNALS OF THE ENTOMOLOGICAL SOCIETY OF AMERICA Vol. 100, no. 3 a food source, and the open end of the test tube was covered with two-ply Kimwipe (Kimwipes EX-L, Kimberly-Clarke, Neehah, WI) secured with rubber tubing to allow ventilation. Adult wasps were removed from the vials 6 h later. The latter were kept in a climatic chamber at 25ЊC and a photoperiod of 12:12 (L:D) h until dissected. Eggs, presumably parasitized by F. dominica, were dissected at different times and checked under a ste- reomicroscope (Leica MZ6, Leica, Wetzlar, Ger- many) with a cold light source (Leica CLS100). Non- parasitized hosts were rejected and the inspection Þnished once 15Ð20 parasitized eggs had been ob- tained. These specimens were mounted on a glass microscope slide in PVA mounting medium (BioQuip Products Co., Rancho Dominguez, CA) for observa- tion by using a light microscope. Immature stages were measured by use of the Eclipse Net software (Nikon 2003). The number of instars was determined using the width of the mandibles (Dyar 1890). Results Ϯ Њ Fig. 1. Egg. em, embryo; pd, pedicel; hc, host chorion. Under laboratory conditions (25 1 C and a pho- toperiod of 12:12 [L:D] h), F. dominica reared on eggs of D. abbreviatus has a developmental time of 18Ð22 d Conocarpus erectus L. (Myrtales: Combretaceae) that from oviposition to adult emergence. Parasitized eggs provided a food source and an oviposition substrate. could be easily recognized by their transparent whit- Wax paper strips (3 by 10 cm) stapled together also ish appearance and unorganized structure when dis- were used as an oviposition substrate (Castillo et al. sected as early as 24 h after exposure to the parasitoid. 2006). Both foliage and paper strips were replaced Conversely, unparasitized eggs have a more opaque every 2Ð3 d. Paper strips containing D. abbreviatus white aspect and show some tissue/organ organization eggs were removed and placed inside a similar cage. when examined. As time progresses, differences be- Adults of F. dominica were introduced into the cage come more conspicuous, and the D. abbreviatus em- and provided honey and water. Presumably, parasit- bryo can be easily observed in the unparasitized egg. ized egg masses were removed from the cage 4Ð5 d Eggs. F. dominica eggs are almost transparent, and later and placed in emergence cages (same dimen- the newly formed larvae become visible as hatching sions as above) supplied with both water and a honey approaches (Fig. 1). Young eggs average 120 Ϯ 3 m food source until adult emergence (Ϸ12 d). in length by 65 Ϯ 3 m in width at the widest point Experimental Specimens. Wax paper strips with (n ϭ 17). The egg is lemon shaped, with a pedicel Ͻ1-d-old eggs were carefully separated from each extending from the anterior end. The maximum length other and cut into one by 0.5-cm strips containing a of the pedicel observed was 176 m. However, this single egg mass, introduced into a glass vial (Fisher- length was highly variable (72 Ϯ 47 m; n ϭ 17) in part brand ßint glass printed white 12- by 75-mm dispos- because of pedicel breakage during dissection. The able culture tubes, Fisher, Pittsburgh, PA) with three pedicel is internally attached to the host egg chorion, naive F. dominica adults Ͻ1 d old. A smear of honey which prevents F. dominica egg from freely moving was provided on the inner surface of each test tube as within the host. Table 1. Measurements (mean ؎ SE in micrometers) of F. dominica immature stages at specified times (in days) after parasitization at 25°C Body Body Tail Mandible Mandible Time Instar n n n n n length width length length width 1 First 17 297 Ϯ 10a 17 107 Ϯ 2aa 17 61 Ϯ 2a 15 30 Ϯ 1a 15 15 Ϯ 5a 2 First 17 694 Ϯ 11b 17 241 Ϯ 8b 15 67 Ϯ 4a 13 31 Ϯ 1a 13 11 Ϯ 1a 3 First 17 884 Ϯ 18c 17 288 Ϯ 17c 17 63 Ϯ 5a 13 31 Ϯ 1a 13 12 Ϯ 1a 4 Second 21 1,064 Ϯ 27d 21 437 Ϯ 13d 14 47 Ϯ 1b 14 10 Ϯ 1a ANOVA F ϭ 398.10 F ϭ 346.15 F ϭ 0.55 F ϭ 17.25 F ϭ 1.34 df ϭ 3, 71 df ϭ 3, 71 df ϭ 2, 48 df ϭ 3, 51 df ϭ 3, 51 P Ͻ 0.00001 P Ͻ 0.00001 P ϭ 0.5789 P Ͻ 0.00001 P ϭ 0.2710 Within columns, values followed by the same letter are not signiÞcantly different (P Ͻ 0.05). a Cephalothorax width. May 2007 JACAS ET AL.: MORPHOLOGY AND DEVELOPMENT OF F. dominica 415 Fig. 2. Neonate Þrst instar. Dorsal view. md, mandibles; mx, maxillae; lg, spiked ligula. Approximately 1 d after oviposition, the embryo the anterior margin of the cephalothorax at this stage increases to 158 Ϯ 6 m in length by 88 Ϯ 4 min of development (Fig.