Changes in surface EMG parameters during static and dynamic fatiguing contractions.

The effect of contraction types on muscle fiber conduction velocity (MFCV), median frequency (MDF) and mean amplitude (AMP) of surface electromyography was examined in the vastus lateralis of 19 healthy male adults. The subjects performed knee extension both statically and dynamically until they were exhausted. The static contraction was a sustained isometric extension of the knee at a joint angle of 90 degrees with 50% of the maximum voluntary contraction (MVC) load. The dynamic contraction was a repetitive isotonic extension of the knee between the angles of 90 degrees and 180 degrees with the same 50% MVC load at a frequency of 10 times per minute. MFVC during the static contraction significantly decreased during the exercise (p < 0.01). On the other hand, MFVC during the dynamic contraction did not significantly change throughout the exercise. MDF decreased and AMP increased during both types of contractions (p < 0.01). Because the blood flow within the muscle is maintained during the dynamic contraction by enhanced venous return from the contracting muscle, these results suggested that MFVC is affected by the metabolic state in the muscle and the changes in MDF cannot be explained only by that of MFVC.     

Possible domestic dispersal of Bactrocera dorsalis during 2015 occurrence on the small islands of south‐western Japan

Although Japan has maintained the state of eradication of the oriental fruit fly, Bactrocera dorsalis Hendel complex (Diptera: Tephritidae) since 1986, B. dorsalis complex are occasionally trapped within a limited area and short time period on Japan's small south‐western islands. Trapping events occurred on Amamioshima Island, Kagoshima Prefecture, in 2015, and male adults were also caught in surveillance traps on neighbouring Tokunoshima (south of Amamioshima) and Yakushima (north of Amamioshima) islands as well as on several islands in Okinawa Prefecture (south of Amamioshima). To investigate possible domestic dispersal of the pest from Amamioshima Island, a trajectory analysis was performed to reveal the timing and flight distance of possible dispersal. Surveillance data indicated that the first trappings on Tokunoshima and Yakushima islands occurred in November, which was after the number of trapped male adults on Amamioshima Island peaked in late October. Backward trajectories from Tokunoshima Island beginning 14 days prior to the first trapping passed over Amamioshima Island, which suggested possible dispersal between the islands. Several backward trajectories from the islands in Okinawa Prefecture also passed Amamioshima Island. Moreover, forward trajectories from Amamioshima Island beginning during peak occurrence, from mid‐October to early November, arrived over Tokunoshima, Iheya and Okinawa islands where the flies were caught. Such circumstantial evidence suggests that domestic dispersal of B. dorsalis complex occurred on Amamioshima Island. A situation similar to that on Tokunoshima Island also occurred on Yakushima Island. However, since the number of traps has been limited until the first capture, it was not clear when and from where the immigrants arrived on the island.     

Influence of contraction force and speed on muscle fiber conduction velocity during dynamic voluntary exercise.

Before using electromyographic (EMG) variables such as muscle fiber conduction velocity (MFCV) and the mean or median frequency (MDF) of an EMG power spectrum as indicators of muscular fatigue during dynamic exercises, it is necessary to determine the influence of a joint angle, contraction force and contraction speed on the EMG variables. If these factors affect the EMG variables, their influence must be removed or compensated for before discussing fatigue. The vastus lateralis of eight normal healthy male adults was studied. EMG signals during non-fatiguing dynamic knee extension exercises were detected with a three-bar active surface electrode array. EMG variables were calculated from the detected signals and compared with the angle of the knee joint, the extension torque and the extension speed. The extension torque was set at four levels with 10% intervals between 40 and 70% of the maximum voluntary contraction. The extension speed was set at five levels with 60 degrees /s intervals between 0 and 240 degrees /s. Because the joint angle unsystematically affected the MFCV, EMG variables at a given joint angle were extracted for comparison. The influence of the extension torque and speed on the extracted EMG variables was clarified with an ANOVA and a regression analysis. The statistical analyses showed that MFCV increased with the extension torque but did not depend on the extension speed. In contrast, MDF was independent of the extension torque but was dependent on the extension speed. MDF thus showed a behavior different from that of MFCV. It became clear that if MFCV is used as an indicator of muscular fatigue during dynamic exercises, it is at least necessary to extract MFCV at a predetermined joint angle and then remove the influence of extension torque on MFCV.     

Genetic variation of the white-spotted longicorn beetle <Emphasis Type="Italic">Anoplophora</Emphasis> spp. (Coleoptera: Cerambycidae) in Japan detected by mitochondrial DNA sequence

Genetic variation of the white-spotted longicorn beetle Anoplophora spp., distributed on the Japanese mainland and the Ryukyu Islands, was examined using nucleotide sequences of mitochondrial DNA. Two fragments, a 1.2-kb-long fragment containing portions of the cytochrome oxidase subunit I and II genes and a 1.4-kb-long fragment containing portions of 16S and 12S rDNAs, were sequenced. In phylogenetic analyses based on the sequences, 294 individuals collected at 75 localities were divided into two major groups (groups A and B) and then split into seven subgroups (A1–A4 and B1–B3). In group A, the closely related subgroups A1, A2, and A3 were mainly distributed on the Japanese mainland and were roughly separated among geographic areas, although the range of A3 spread significantly from Kyushu to the Central Ryukyu Islands. The sequence of A4, detected from one individual collected in eastern Honshu, was almost the same as that reported for A. chinensis (Forster) on the Chinese continent. In group B, subgroups B1 and B2 were restricted to the Central and Southern Ryukyu Islands, respectively, while B3 was distributed widely in both regions. Based on the results, we discuss the geographic origin of the haplotypes and movement of the insects between geographic areas.     

Mating disruption for control of Melanotus okinawensis (Coleoptera: elateridae) with synthetic sex pheromone

A mating disruption experiment to control Melanotus okinawensis Ohira (Coleoptera: Elateridae) was conducted at a sugarcane (Saccharum spp.) field and a wild Japanese pampas, Miscanthus sinensis Anderss, grassland on Minami-Daito Island (3,057 ha) from 2001 to 2007. The sugarcane field and the pampas grassland were treated with synthetic sex pheromone that evaporated from a polyethylene tube dispenser. The mean total catches obtained by monitoring traps in the sugarcane fields decreased by 96.1% in 2001 from the previous year on Minami-Daito Island. The mean total trap catches in the treated area further decreased by 74.0% from 2001 until 2007 as cumulative effects. Simultaneously, the number of adults captured by hand decreased from 4.7 per sugarcane field in 2001 to 0.5 in 2007 (89.3% reduction), whereas those captured in the untreated area (Miyagi Island) did not show such a decrease. The mating rates were significantly lower in the females captured in the treated area (14.3-71.4%) than those in the untreated area (96.9-100%). However, the amount of the decrease in the trap catches was relatively small at first (39.6% reduction) in the Japanese pampas grassland on the periphery of the Island. This was probably due to the loss of pheromone substance caused by the strong seasonal wind in the periphery. However, mean total trap catches at the periphery also decreased within several years; significant decreases were detected until 2003, 2006, and 2007. These results indicated that the mating disruption effectively reduced an isolated population of M. okinawensis.     

Estimation of dispersal distance by mark-recapture experiments using traps: correction of bias caused by the artificial removal by traps

Although in mark-recapture experiments traps are useful to estimate the dispersal distance of organisms, they cause a dilemma that may be called a kind of Heisenberg effect: a large number of traps should be placed to yield a precise estimate of mean dispersal distance, while these traps shorten the mean dispersal distance itself by intercepting organisms that should have dispersed for further distances. We propose a procedure to solve this dilemma by placing traps uniformly in a lattice pattern, and by assuming a random movement and a constant rate of settlement for organisms. We applied this procedure to estimate the dispersal distance of the sugarcane wireworm Melanotus okinawensis Ohira (Coleoptera: Elateridae). The estimated mean dispersal distance was 143.8 m. Through the use of a conventional method of estimation, the mean dispersal distance was estimated to be 118.1 m. Thus, it was shown that the conventional estimate of dispersal distance was 18% smaller than the corrected estimate in our experiment.     

Infection Density Dynamics of the Citrus Greening Bacterium “Candidatus Liberibacter asiaticus” in Field Populations of the Psyllid Diaphorina citri and Its Relevance to the Efficiency of Pathogen Transmission to Citrus Plants

Huanglongbing, or citrus greening, is a devastating disease of citrus plants recently spreading worldwide, which is caused by an uncultivable bacterial pathogen, “Candidatus Liberibacter asiaticus,” and vectored by a phloem-sucking insect, Diaphorina citri. We investigated the infection density dynamics of “Ca. Liberibacter asiaticus” in field populations of D. citri with experiments using field-collected insects to address how “Ca. Liberibacter asiaticus” infection density in the vector insect is relevant to pathogen transmission to citrus plants. Of 500 insects continuously collected from “Ca. Liberibacter asiaticus”-infected citrus trees with pathological symptoms in the spring and autumn of 2009, 497 (99.4%) were “Ca. Liberibacter asiaticus” positive. The infections were systemic across head-thorax and abdomen, ranging from 10³ to 10⁷ bacteria per insect. In spring, the infection densities were low in March, at ∼10³ bacteria per insect, increasing up to 10⁶ to 10⁷ bacteria per insect in April and May, and decreasing to 10⁵ to 10⁶ bacteria per insect in late May, whereas the infection densities were constantly ∼10⁶ to 10⁷ bacteria per insect in autumn. Statistical analysis suggested that several factors, such as insect sex, host trees, and collection dates, may be correlated with “Ca. Liberibacter asiaticus” infection densities in field D. citri populations. Inoculation experiments with citrus seedlings using field-collected “Ca. Liberibacter asiaticus”-infected insects suggested that (i) “Ca. Liberibacter asiaticus”-transmitting insects tend to exhibit higher infection densities than do nontransmitting insects, (ii) a threshold level (∼10⁶ bacteria per insect) of “Ca. Liberibacter asiaticus” density in D. citri is required for successful transmission to citrus plants, and (iii) D. citri attaining the threshold infection level transmits “Ca. Liberibacter asiaticus” to citrus plants in a stochastic manner. These findings provide valuable insights into understanding, predicting, and controlling this notorious citrus pathogen.     

Dependence of average muscle fibre conduction velocity on voluntary contraction force

Average muscle fibre conduction velocity (CV) measured with multichannel surface electrodes decreases with time during sustained isometric contraction. Based on this property, CV is considered a candidate for an objective index to localized muscular fatigue. CV, however, also depends on many other factors that include muscle temperature and voluntary contraction force. In this paper, the effect of contraction force on CV was studied by defining not only the target force level but also the whole force trajectory. The contraction was isometric and lasted 14 s. The target force was set at four levels from 30% to 90% of the maximal voluntary contraction (MVC). Three typical muscles were studied in seven healthy male subjects. In the vastus lateralis, CV increased with contraction force in many cases. In the biceps brachii, CV decreased rapidly with time before the contraction force reached the target levels of 70% or 90% MVC. At these force levels, CV was smaller than that at 50% MVC. CV in the biceps consequently showed no apparent dependence on the contraction force. The tibialis anterior showed intermediate change in CV between the vastus lateralis and the biceps brachii. These results indicate that CV basically increases with contraction force, but this relationship becomes unclear when CV decreases rapidly with time.