Toshio Ichikawa

Structure of Neurosecretory Cells with Immunoreactive Diapause Hormone and Pheromone Biosynthesis Activating Neuropeptide in the Silkworm, Bombyx mori

Abstract Immunocytochemistry of diapause hormone (DH) or pheromone biosynthesis activating neuropeptide (PBAN) revealed three clusters of neurosecretory cells present on the ventral midline of the suboesophageal ganglion (SG) of the silkworm: there were 4 cells in the anterior, 6 cells in the medial, and 2 cells in the posterior cluster. Intracellular injection of Lucifer Yellow into an anterior or a medial cell revealed that the cell has a dendritic arborization at the anterior region of the SG and that it projects an axon to the corpus cardiacum (CC) via a branch of the maxillary nerve and an associated nerve of the CC (NCC-V). A dye-filled posterior cell in the larva projects bilaterally-symmetric dendritic branches to the anterior half of the SG that is to expand laterally to fuse the brain after pupation. The axon of the cell, passing through the brain, enters the NCC 3 to spread varicose terminal branches in the CC and associated nerves of the CC.

Distribution of color receptors in the larval eyes of four species of lepidoptera

Summary1.Caterpillars of the noctuid mothMamestra brassicae have six stemmata (I-VI) on either side of the head. Each stemma has seven photoreceptor cells (Fig. 1). Photoreceptor cells are spectrally differentiated into three types: UV, blue, and green (Fig. 2).2.Stemmata I and III have five green and two blue receptors; stemmata II, V, and VI have four green, one blue, and two UV receptors; stemma IV has five green and two UV receptors (Table 1).3.The spectral sensitivities of all photoreceptor cells inMamestra except for one, R4 of stemma IV, are the same as those of the anatomically equivalent cells inPapilio xuthus (Fig. 3). The R4 of IV in the former is a green receptor, while in the latter it is a blue receptor.4.The fact that the R4s of stemma IV inMamestra andPapilio differ from each other physiologically may be related to the phylogenetic distance between the two species. Support for this point of view comes from the finding that inBombyx mori, thought to be relatively closely related toMamestra, the R4 in stemma IV is a green receptor (Fig. 6) while inPieris rapae crucivora more closely related toPapilio it seems to be a blue receptor (Table 2).

Cellular patterns and spectral sensitivity of larval ocelli in the swallowtail butterflyPapilio

SummaryCaterpillars of the swallowtail butterflyPapilio xuthus L. like most lepidopterans have six larval ocelli (stemmata) on each side of the head (Fig. 1). Five of these (II–VI) are arranged in a close ellipsoidal cluster from which number I is somewhat isolated ventrally (Fig. 2). Each stemma has seven retinular cells (R) organized in two tiers (proximal and distal, Fig. 3) but the cellular patterns and spectral sensitivities fall into three classes. As proved by intracellular recordings (Fig. 4) stemmata I and III have five green receptors (λmax ca. 530 nm) and two blue ones (λmax ca. 450 nm) (Fig. 5). The other ocelli have only four green and one blue cell, but have in addition two UV units each (λmax ca. 370 nm); in II and IV one green cell (R6) is proximally located (Fig. 6), in V and VI it is distal. All distal cells whether three (I–IV) or four (V, VI) in number are green units. Hence all blue and UV receptors are in the proximal cell tier with UV limited to R5 and R7, blue to R4, R5, and R7 (Fig. 7).

Functional Differentiation of Neurosecretory Cells with Immunoreactive Diapause Hormone and Pheromone Biosynthesis Activating Neuropeptide of the Moth, Bombyx mori

Abstract The suboesophageal ganglion of the silkworm, Bombyx mori, contains three clusters of neurosecretory cells that are imrnunoreactive with antisera against the diapause hormone (DH) and the pheromone biosynthesis-activating neuropeptide (PBAN), the two neurohormones that are generated from a common precursor protein. The cells lie on the ventral midline of the ganglion. Neurosecretory cell clusters responsible for the diapause induction activity and the pheromonotropic activity of females were determined by surgically removing one or two of the three clusters of the DH/ PBAN imrnunoreactive cells. A potent diapause induction activity was obtained in females retaining a posterior cluster of cells while a strong pheromonotropic activity was obtained in case of females with a medial cluster. The functional differentiation of these cells may relate to different biochemical and/or physiological natures.

Larval Cannibalism and Pupal Defense Against Cannibalism in Two Species of Tenebrionid Beetles

Cannibalism of pupae by larvae has been documented in many species of insects, but the features of larval cannibalism and pupal defensive mechanisms against larval cannibalism have been largely ignored. Pupae of tenebrionid beetles rotate their abdominal segments in a circular motion in response to the tactile stimulation of appendages, including legs, antennae, maxillary pulps, and wings. When the pupal abdominal rotation responses of Tenebrio molitor and Zophobas atratus were completely blocked by transecting the ventral nerve cord (VNC) of the pupae, the appendages of the paralytic pupae became initial, major targets for attack by larval cannibals. The majority of 20 paralytic pupae was cannibalized by 100 larvae within 6 h, and almost all the pupae were killed within 2–3 days. In contrast, only a few pupae of Z. atratus and several pupae of T. molitor were cannibalized when the VNC was intact. The abdominal rotation response of the pupae thus functions as an effective defense against larval cannibalism.

Periodic abdominal pumping supports leg development during metamorphosis in tenebrionid beetle Zophobas atratus.

Rhythmic abdominal pumping movements in a pupa of giant mealworm beetle Zophobas atratus caused large hemolymph pressure pulses of approximately 20 mmHg. The abdominal pumping movements were completely blocked by transecting the ventral nerve cord (VNC) between the first and second abdominal ganglia. Transection of the VNC until 2 days after pupation caused a developmental defect of adult legs: morphogenesis of the tibial and tarsal segments was severely retarded, and the segments remained covered with a thick pupal cuticle. The developmental defect was rescued by artificially inducing rhythmic abdominal bending for 3 days after transection of VNC. Blocking of the abdominal pump did not increase the amount of water loss during the pupal period. The transplanted tibial segments lacking active tracheal ventilation could form a thick adult cuticle. The results suggest that abdominal pumping movements during the pupal period support the development of adult legs by facilitating hemolymph circulation.

Firing activities of neurosecretory cells producing diapause hormone and its related peptides in the female silkmoth, Bombyx mori. I. labial cells.

Abstract There are three known clusters of neurosecretory cells expressing a gene encoding dia-pause hormone (DH) and four related peptides in the suboesophageal ganglion (SOG) of Bombyx mori. Long-term chronic recordings were made from the axonal tract (NCC-3) of a pair of cells localized in the labial (posterior) neuromere of SOG during pupal-adult development. There was a significant difference in firing activity patterns of the labial neurosecretory cells between diapause-egg and non-diapause-egg producers: labial cells in the former were active throughout pupal-adult development, whereas the same cells in the latter usually maintained an inactive state until the last quarter of pupal-adult development, a time at which a secretion of DH seems to be too late to act on the developing ovary for the induction of dia-pausing eggs. This observation strongly supports the notion that labial cells release DH and are responsible for determination of embryonic diapause in the silkmoth.

Neural Inactivation of Sex Pheromone Production in Mated Females of the Silkworm Moth, Bombyx mori

Abstract Pheromone content in the pheromone gland of the female moth, Bombyx mori, declines after mating with a time course closely resembling that of decapitated females. The inactivation of pheromone production after mating was prevented when the ventral nerve code or a pair of peripheral nerves (N4) extending from the terminal abdominal ganglion was severed before mating. In contrast, the post-mating inactivation of pheromone production was not prevented when the ventral nerve cord was transected 1 hr after the initiation of mating. Although females produced only a small amount of pheromone when the connection between the brain and the suboesophageal ganglion (SG) was cut at an early pupal stage, mating did not induce a significant decline of pheromone production in these females. The results suggest that inactivation of pheromone production is mediated by a neural signal, originating from a peripheral receptor, that is sent via the ventral nerve cord to the brain-SG complex to suppress activity of the neurosecretory cells responsible for the release of pheromonotropic neuropeptides, such as a pheromone biosynthesis activating neuropeptide (PBAN).

Circadian Firing Activities of Neurosecretory Cells Releasing Pheromonotropic Neuropeptides in the Silkmoth, Bombyx mori

Abstract Neurosecretory cells releasing the pheromone biosynthesis-activating neuropeptide (PBAN) in Bombyx mori exhibit diurnal firing activity. Diel changes in the firing activity of the PBAN producing cells persisted in both constant dark and constant dim light (0.1 lx) at mean periods of 23.0± 1.6 hr and 22.6± 0.8 hr, respectively, thereby suggesting that the neurosecretory cell system is under the control of a circadian pacemaker. The circadian firing rhythm was greatly modified by background illumination: (1) the period of free-running activity rhythm was significantly short (18.5± 1.6 hr) under continuous illumination of a moderate intensity (100 lx) and (2) the duration of a firing period of cells elongated by 2.1± 0.7 hr, when light intensity during a photophase was lowered to 0.01 lx. The suppressive effect of light on the firing activity may induce a nocturnal component of a daily activity pattern by releasing PBAN cells from suppression after termination of illumination.

Receptive field of the stemmata in the swallowtail butterflyPapilio

SummaryReceptive fields of individual retinular cells in the stemmata ofPapilio xuthus L. were examined electrophysiologically, and the receptive field of the complete stemmatal system was reconstructed (Fig. 8).In stemmata I-IV, proximal retinular cells have narrow receptive fields (acceptance angles of Δϱ = 1.7–5 °, Fig. 5) and small inclinations of the visual axes (inclinations of θ = 0.7–1.5 °, Fig. 2) with respect to the axis of the stemma, while distal ones have wide fields (Δϱ =7–13 °, Fig. 5) and large inclinations of the visual axes (θ = 5–10 °, Fig. 3). In stemmata V and VI, both proximal and distal retinular cells have wide receptive fields (Δϱ = 7–26 °, Fig. 6) and have large inclinations of their visual axes (Δ = 9–19 °) with respect to the axis of the stemma except for one proximal cell (θ = 0 °) (Fig. 4).The spatial properties of distal and proximal retinular cells, combined with the finding that distal cells are homogeneous in the spectral sensitivity while proximal ones are heterogeneous (Ichikawa and Tateda 1980), suggest that the distal cells may be concerned largely with the detection of objects and proximal cells are involved with the discrimination of the color and shape of the detected objects.