Norio Hirai

Aerodynamic forces and vortical structures in flapping butterfly's forward flight

Forward flights of a bilaterally symmetrically flapping butterfly modeled as a four-link rigid-body system consisting of a thorax, an abdomen, and left and right wings are numerically simulated. The joint motions of the butterflies are adopted from experimental observations. Three kinds of the simulations, distinguished by ways to determine the position and attitude of the thorax, are carried out: a tethered simulation, a prescribed simulation, and free-flight simulations. The upward and streamwise forces as well as the wake structures in the tethered simulation, where the thorax of the butterfly is fixed, reasonably agree with those in the corresponding tethered experiment. In the prescribed simulation, where the thoracic trajectories as well as the joint angles are given by those observed in a free-flight experiment, it is confirmed that the butterfly can produce enough forces to achieve the flapping flights. Moreover, coherent vortical structures in the wake and those on the wings are identified. The g...

Effects of structural flexibility of wings in flapping flight of butterfly.

The objective of this paper is to clarify the principle of stabilization in flapping-ofwings flight of a butterfly, which is rhythmic and cyclic motion. For this purpose, a dynamics model of a butterfly is derived by Lagranges method, where the butterfly is considered as a rigid multi-body system. For the aerodynamic forces, a panel method is applied. Validity of the mathematical models is shown by agreement of the numerical result with the measured data. Then, periodic orbits of flapping-of-wings flights are searched in order to fly the butterfly models. Almost periodic orbits are obtained, but the model in the searched flapping-of-wings flight is unstable. This research, then, studies how the flexibly torsional wings effect on the flight stability. Numerical simulations demonstrate that the flexible torsion reduces the flight instability. Moreover, this study develops a precise flexibility model to discuss the effect based on the actual deformation induced by aerodynamic force.

Modeling and emergence of flapping flight of butterfly based on experimental measurements

The objective of this paper is to clarify the principle of stabilization in flapping-of-wing flight of a butterfly, which is a rhythmic and cyclic motion. For this purpose, a dynamics model of a butterfly is derived by Lagranges method, where the butterfly is considered as a rigid multi-body system. For the aerodynamic forces, a panel method is applied. Validity of the mathematical models is shown by an agreement of the numerical result with the measured data. Then, periodic orbits of flapping-of-wing flights are searched in order to fly the butterfly models. Almost periodic orbits are obtained, but the model in the searched flapping-of-wing flight is unstable. This research, then, studies how the wake-induced flow and the flexibly torsional wings effect on the flight stability. Numerical simulations demonstrate that both the wake-induced flow and the flexible torsion reduces the flight instability. Because the obtained periodic flapping-of-wing flight is unstable, a feedback control system is designed, and a stable flight is realized.

Effects of Morphological Characteristics of Cucumis sativus Seedlings Grown at Different Vapor Pressure Deficits on Initial Colonization of Bemisia tabaci (Hemiptera: Aleyrodidae)

ABSTRACT We investigated the effects of morphological characteristics of cucumber, Cucumis sativus L., seedlings grown at different vapor pressure deficits (VPDs) on initial colonization of whitefly Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) biotype B. The seedlings were grown at a VPD of 3.8 or 0.4 kPa for 9 d at 30°C under a photoperiod of 12:12 (L:D) h. Pairs of seedlings, one grown at high VPD and the other at low VPD, were then installed in cages with a VPD of 1.3 kPa, and adults of B. tabaci between 150 and 200 were released. Leaves of high-VPD seedlings had fewer B. tabaci than those of low-VPD seedlings 24 h after release. They also had higher relative chlorophyll content, were thicker and tougher, and had abaxial trichomes with higher density. Water stress caused by the high VPD probably decreased the initial colonization of B. tabaci through changes in these leaf morphological characteristics.

Atmospheric Humidity Influences Oviposition Rate of Tetranychus urticae (Acari: Tetranychidae) Through Morphological Responses of Host Cucumis sativus Leaves.

Abstract We investigated the effects of morphology of host cucumber, Cucumis sativus L., leaves acclimatized to different atmospheric humidity levels on oviposition by adult females of the twospotted spider mite, Tetranychus urticae Koch. Cucumber seedlings were grown at a vapor pressure deficit (VPD) of 0.4, 1.9, or 3.0 kPa at 28°C (90%, 50%, or 20% relative humidity, respectively) in growth chambers until the second true leaves had expanded. Adult females of T. urticae were released on the adaxial surfaces of leaf squares cut from first and second true leaves in each treatment group, and held in the same humidity condition. Eggs were counted 2 d after release. The lower acclimatization humidity (higher VPD) increased trichome (leaf hair) density of the host leaves and oviposition rate, but the relationship between the trichome and oviposition differed between leaf positions. The leaf mass per area (LMA) was greater in first true leaves than in second true leaves, but was not influenced by VPD. A linear regression model with oviposition rate as the dependent variable and trichome density and LMA as independent variables showed that both variables influenced the oviposition rate approximately equally. We conclude that oviposition was accelerated under low humidity (high VPD) conditions indirectly probably through an increase in the trichome density of host leaves.

Genital segments of sexual mosaic offspring from Wolbachia-infected female Zizina emelina (Lepidoptera: Lycaenidae).

ABSTRACT: Eight sexual mosaic offspring of Zizina emelina (Lepidoptera: Lycaenidae) were obtained from females infected with male-killing Wolbachia (wEmeTn2), though they were mostly dead at the stage of pharate adult. Uninfected females or females infected with another strain of Wolbachia (wEmeTn1) produced no mosaics. Therefore, the occurrence of these sexual mosaics was associated with wEmeTn2 infection. In sexual mosaics, the ventral and dorsal parts of genitalia differentiated independently into male-specific and female-specific formations, respectively, i.e., the ventral part of abdominal segment IX may have tendencies to retain male structures, while the dorsal parts of abdominal segments IX and X possess female structures. More than two pairs of ill-developed valvae were observed in several individuals in a deep pouch. The presence of additional valvae would mean that the segment IX or the ventral phallic lobe is at least partly duplicated.

Controlling Flow Structures by Wing Motion in a Flapping-Flight Model

We have studied flow control in a two-dimensional flapping flight model for insects. The insects center-of-mass motion can move in both horizontal and vertical directions according to the hydrodynamic force generated by flapping. Under steady flapping motion, the model converges to steady flight states depending on initial conditions. Further, we show that a short-time wing stop can control the final steady flight states. The models flight finally converges to a final state by way of another quasi-steady state, which is not observed as a (stable) steady flight.

Reproduction, growth rate and dispersal of the dark chub, Candidia sieboldii, as estimated by using the mark–release–recapture method

ABSTRACT We investigated the breeding season, growth rate and dispersal of the dark chub, Candidia sieboldii, an endangered species in Japan. A mark–release–recapture survey was performed in three branches of the Ishizu River system in Osaka Prefecture, Japan, between May 2012 and August 2013. A total of 963 individuals were marked in one river branch and 275 (29%) were recaptured at least once in the same river section. The breeding season was determined to be June–August, and the size at maturity for both males and females was estimated at about 70 mm standard length. Growth rates calculated from standard lengths of recaptured individuals were higher between April and September than between October and March. Among 963 marked individuals, only a single fish was found 500 m downstream from the release point. Moreover, although we released 409 more marked individuals in the three branches to follow inter-branch dispersal between September and December 2013, we observed none. These results indicate that this species has low dispersal and a short lifespan of 1–2 years. This short lifespan could increase the risk of breeding failure, and the low frequency of dispersal, restricted by weirs, could make population re-establishment and recovery difficult.

Genetic population structure of the fluvial eight-barbel loach Lefua sp. 1 in the three river systems in central Honshu, Japan, revealed by microsatellite DNA markers

The fluvial eight-barbel loach Lefua sp. 1 is an undescribed species distributed from the Kinki to Chugoku districts, Honshu, and also on Shikoku Island, Japan. Genetic relationships among local populations are unclear and management units remain undetermined. To aid conservation, we determined genetic population structures from microsatellite loci for 20 populations from three river systems on Honshu. The genetic diversity within populations is relatively low; the majority has experienced genetic bottlenecks. Statistical analysis revealed significant divergence among river systems suggesting that each should be recognized as a management unit. Any conservation program should consider the populations’ genetic uniqueness.

Differences in pupal cold hardiness and larval food consumption between overwintering and non‐overwintering generations of the common yellow swallowtail, Papilio machaon (Lepidoptera: Papilionidae), from the Osaka population

To clarify differences in pupal cold hardiness and larval food consumption between overwintering and non‐overwintering generations of the common yellow swallowtail, Papilio machaon, we reared larvae from the Osaka population under photoperiods of 16 h light : 8 h dark (LD 16:8) (long day) or LD 12:12 (short day) at 20°C. We examined the relationship between food consumption and weight during the final larval stadium and pupae, and measured the pupal supercooling point (SCP). Although the ratio of assimilation to consumption did not differ significantly between photoperiods, the ratio of assimilation to pupal weight differed significantly between individuals reared under long and short days. All diapausing pupae were brown, whereas 56% of non‐diapausing pupae were green with the remainder brown. The mean pupal body length (L), dorsal width (W1) and lateral width (W2) were larger in non‐diapausing than in diapausing pupae, and the W1/L and W1/W2 ratios differed significantly between non‐diapausing and diapausing pupae. SCP was approximately –20°C and did not differ among pupae 5, 15 and 30 days after pupation under long‐day conditions. However, under short‐day conditions, mean SCP gradually decreased, stabilizing at approximately –24 to –25°C by 30 days after pupation. After freezing, some diapausing pupae emerged as adults, whereas all non‐diapausing pupae died. Both egestion and assimilation were greater under long‐day conditions. The results revealed that pupae of this papilionid exhibit seasonal polyphenism in physiological and morphological traits. Energy from food appears to be expended on increasing cold hardiness in the overwintering generation and on reproduction in the non‐overwintering generation.