Embryogenesis of the Codling Moth, Cydia pomonella (Lepidoptera: Tortricidae) JOHN R. RUBERSON, 1 JOSEPH R. LARSEN, 2 AND CLIVE D. JORGENSEN Department of Zoology, Brigham Young University, Provo, Utah 84602 Ann. Entomol. Soc. Am. 80: 561-570 (1987) ABSTRACT Embryonic development of the codling moth, Cydia pomonella (L.), was examined. The germ band forms in the posterior region of the egg at 7 h. Gastrulation begins at 15 h. The stomodeum invaginates at 22 h, followed by the proctodeum at 24 h. The midgut rudiment arises at 44 h by fusion of anterior and posterior mesenteron rudiments. The midgut closes between 52 and 54 h, nearly simultaneous with dorsal closure. Neuroblasts appear at 20 h, brain formation begins at 24 h, and ventral nerve cord is defined by 44 h. Perineurium appears to originate from somatic mesoderm. Formation of the tracheal system begins at 32 h, and is complete by 78 h. Germ cells arise at 7 h in the anterior pole, migrate in to the germ band at 14 h, and are associated with it by 16 h. Gonads are present by 58 h. KEY WORDS Cydia pomonella, histogenesis, embryology EARLY INTERPRETATIONS of embryological devel- opment of the codling moth, Cydia pomonella (L.), were based largely on external examinations of morphological development (Wiesmann 1935, Voyadjoglou 1976, Richardson et al. 1982). All three studies assumed development paralleled that re- ported for other tortricids (Richardson et al. 1982). Fragments of tortricid embryogenesis have been reported in three early studies: formation of the germ band in Eudemis naevana (Hiibner) (Huie 1918), one paragraph on codling moth embryo- genesis (Weismann 1935), and an unpublished dis- sertation that outlined histogenesis of Grapholitha molesta (Busck) (Rutschky 1949). Several studies of tortricid embryogenesis have been reported since 1960 (Stairs 1960, Bassand 1965, Reed & Day 1966, Anderson & Wood 1968, Voyadjoglou 1976, Rich- ardson et al. 1982). Histogenesis was limited to three of these studies: Stairs (1960), Choristoneura fumiferana (Clemens); Bassand (1965), Zeiraphera griseana (Hiibner); and Anderson & Wood (1968), Epiphyas postvittana (Walker). These accounts* correlate with one another and with the work re- ported earlier by Rutschky (1949); therefore, the assumption that codling moth embryogenesis is also comparable (Richardson et al. 1982) has some va- lidity, although specific data are not available to support it. Development of the codling moth requires 108 h for eclosion at 29°C, and the organ systems are essentially complete halfway through embryonic development; therefore, the first 66 h were studied more critically in our research than the remaining 42 (Table 1). Our study provides the first inter- 1 Current address: Dep. of Entomology, Cornell Univ., Ithaca, NY 14853. 2 Dep. of Entomology, Univ. of Illinois, Urbana, IL 61801. pretative description of codling moth histogenesis and compares it with that reported for other tor- tricids. Materials and Methods Codling moth eggs were obtained from a labo- ratory colony maintained at 25°C and a photope- riod of 16:8 (L:D). Plastic sheets cut from storage bags (10 by 20 cm; Nasco WHIRL-PAK, Modesto, Calif.) were provided as an oviposition substrate. Inner surfaces of the bags were ideal because the eggs could be easily removed from them using a camel's-hair brush. All eggs were ca. 0.5 h old when they were removed from the plastic sheets. They were then incubated at 29°C (60-80%RH) until the desired developmental stages were reached. Age-specific groups of eggs were fixed hourly until 20 h, every 1-2 h until 66 h, and every 6-8 h thereafter until eclosion. Chorions of all eggs younger than 10 h were pricked and sometimes physically removed from older eggs to allow better penetration of the fixative. Eggs were fixed in 4.0% glutaraldehyde, washed in 0.1 M phosphate buffer, dehydrated, and em- bedded in methacrylate (Moretti & Larsen 1973). Before polymerization, eggs in methacrylate were held 2-3 d in a vacuum to improve infiltration of plastic. After polymerization, embedded eggs were serially sectioned at a thickness of 0.8-1.0 (im. The sections were stained with Delafield's hemotoxylin and counter-stained with eosin (Kennedy 1949). Some stages were examined with a scanning elec- tron microscope, and whole mounts of others were stained briefly in aceto-orcein, then mounted in euparal on microslides. 561