A NOVEL METHOD FOR STUDYING THRESHOLD LEVELS FOR POSITIVE PHOTOTAXIS IN INSECTS

This paper presents a novel method for studying threshold levels for positive phototaxis of insects and smaller mobile organisms. Outdoor lighting affects light sensitive species and there is a need to evaluate the effect of light levels, spectral composition of the light and light distribution to mitigate the ecological impacts of the artificial light. For this purpose, a test box investigating the effect of light on insects in a controlled manner has been constructed. The box is equipped with a luminance source and the light levels can be varied from a maximum value continuously down to zero. The spectral composition of the light can be varied by changing the lamp or using optical filters. For visibility of the insects the box has infrared light emitting diodes in the ceiling and two wide-angle cameras monitor the light response. The functionality of the box is tested with the species greater wax moth.

Characterization of Chlamydomonas reinhardtii Mutants That Exhibit Strong Positive Phototaxis

The most motile phototrophic organisms exhibit photo-induced behavioral responses (photobehavior) to inhabit better light conditions for photosynthesis. The unicellular green alga Chlamydomonas reinhardtii is an excellent model organism to study photobehavior. Several years ago, we found that C. reinhardtii cells reverse their phototactic signs (i.e., positive and negative phototaxis) depending on the amount of reactive oxygen species (ROS) accumulated in the cell. However, its molecular mechanism is unclear. In this study, we isolated seven mutants showing positive phototaxis, even after the induction of negative phototaxis (ap1~7: always positive) to understand the ROS-dependent regulatory mechanism for the phototactic sign. We found no common feature in the mutants regarding their growth, high-light tolerance, and photosynthetic phenotypes. Interestingly, five of them grew faster than the wild type. These data suggest that the ROS-dependent regulation of the phototactic sign is not a single pathway and is affected by various cellular factors. Additionally, the isolation and analyses of mutants with defects in phototactic-sign regulation may provide clues for their application to the efficient cultivation of algae.

Effects of Light Intensity and Wavelength on the Phototaxis of the Crassostrea gigas (♂) and Crassostrea sikamea (♀) Hybrid Larvae

Light sensitivity is important for marine benthic invertebrates, and it plays a vital role in the oysters settling. Generally, the emerging of eyespot is a signal of oyster larvae settling, while like most of the other coastal species, the oysters are threatened by artificial light pollution. Crassostrea gigas and Crassostrea sikamea are two oyster species naturally distributed in China, and their hybrids are potential material for oyster cross-breeding. Therefore, we investigated the phototaxis of hybrid eyespot larvae and eyeless larvae under different light intensities and wavelengths to uncover how light affects their behaviors. The results indicated that hybrid oyster larvae had positive phototaxis to specific light intensity and wavelength. We further concluded that 5 lx was the positive phototaxis light intensity for the eyeless hybrid larvae, and that the acceptable light intensity range of the eyespot hybrid larvae expanded to 5–10 lx, but no higher than 15 lx; besides, the hybrid larvae behaved negatively to the light over 25 lx. The present study also suggested the positive effects of green light on larvae gathering and the induction of red light on eyespot larvae settling. In conclusion, our study may contribute to the understanding of phototaxis of hybrid oyster larvae, as well as the further perspective of light pollution on benthic communities and coastal system restoration.

Invasive Pest and Disease Pathogen as Sneakers in Railways for Their Spread in Different Ecological Region: A New Report

A new pathway of travels by invasive pest and disease pathogen through railways, as sneakers, were noticed for the first time. The Indian railways passing through the soybean fields infested with Spodoptera litura, after evening attracted the moth of Spodoptera by the illuminating lights in the railways compartment and the moth enters into the compartment through open compartment windows. These moths remain in the railway compartment until the dawn and get out of the compartment as the early morning sun light enters into the compartments and are thus the sneakers crop pest in railways due to their unnoticed travels/transport. Such sneakers crop pest travels up to a distance of 600 km during the period of night from one ecological region to another ecological region having the same crop to infest or the alternative host crop of the pest to cause the fresh infestation. This phenomenon of pest travel was observed in the region of Lalitpur in Uttar Pradesh, India, having soybean infestation. This is a quick travel by the pest into different areas, unseen and unreported earlier and may occur in any part of the world where the railways pass through the infested crop areas and attract the positive phototaxis pest and transport them, as sneakers, in to another ecological region. In another instance, the Sigatoka disease pathogen of banana was also noticed to travels from one ecological region to another ecological region through the railways, as sneakers without notice. This phenomenon of disease pathogen’s travels was noticed in Jalgaon region from where the banana produce is transported to different parts of India. In the trading and transport of banana through railways, the loaders use the banana leaves infected with the sigatoka pathogen as a packaging material for banana bunches while loading the banana produce in the railway wagons for their transportation. Thus, the sigatoka pathogen travels up to a distance of 1200 km/day along with the banana produce through the railways. The sigatoka infected leaves, with the unloading of banana produce also sneaks into the new ecological region and spread to infect the banana crop available in the region. Thus, the positive phototaxis insect pest are the sneakers in the railways for their travels while diseases pathogens with healthy crop produce travels and embarks to sneaks into a new ecological region and thus the railways transport system unintentionally transport the crop pest and disease pathogen from one ecological region to another. The knowledge of this new travel pathway will be useful in finalizing the strategies of plant quarantine and management of invasive pest and disease pathogens.

Antarctic krill (Euphausia superba) exhibit positive phototaxis to white LED light

The use of light-emitting diodes (LEDs) is increasingly used in fishing gears and its application is known to trigger negative or positive phototaxis (i.e., swimming away or toward the light source, respectively) for some marine species. However, our understanding of how artificial light influences behavior is poorly understood for many species and most studies can be characterized as trial and error experiments. In this study, we tested whether exposure to white LED light could initiate a phototactic response in Antarctic krill (Euphausia superba). Trawl-caught krill were used in a controlled artificial light exposure experiment conducted onboard a vessel in the Southern Ocean. The experiment was conducted in chambers with dark and light zones in which krill could move freely. Results showed that krill displayed a significant positive phototaxis. Understanding this behavioral response is relevant to development of krill fishing technology to improve scientific sampling gear, improve harvest efficiency, and reduce potential unwanted bycatch.

Artificial light and biting flies: the parallel development of attractive light traps and unattractive domestic lights

Light trapping is an important tool for monitoring insect populations. This is especially true for biting Diptera, where light traps play a crucial role in disease surveillance by tracking the presence and abundance of vector species. Physiological and behavioural data have been instrumental in identifying factors that influence dipteran phototaxis and have spurred the development of more effective light traps. However, the development of less attractive domestic lights has received comparatively little interest but could be important for reducing interactions between humans and vector insects, with consequences for reducing disease transmission. Here, we discuss how dipteran eyes respond to light and the factors influencing positive phototaxis, and conclude by identifying key areas for further research. In addition, we include a synthesis of attractive and unattractive wavelengths for a number of vector species. A more comprehensive understanding of how Diptera perceive and respond to light would allow for more efficient vector sampling as well as potentially limiting the risk posed by domestic lighting.

Artificial Light Increases Local Predator Abundance, Predation Rates, and Herbivory

Human activity is rapidly increasing the radiance and geographic extent of artificial light at night (ALAN) leading to alterations in the development, behavior, and physiological state of many organisms. A limited number of community-scale studies investigating the effects of ALAN have allowed for spatial aggregation through positive phototaxis, the commonly observed phenomenon of arthropod movement toward light. We performed an open field study (without restricted arthropod access) to determine the effects of ALAN on local arthropod community composition, plant traits, and local herbivory and predation rates. We found strong positive phototaxis in 10 orders of arthropods, with increased (159% higher) overall arthropod abundance under ALAN compared to unlit controls. The arthropod community under ALAN was more diverse and contained a higher proportion of predaceous arthropods (15% vs 8%). Predation of immobilized flies occurred 3.6 times faster under ALAN; this effect was not observed during the day. Contrary to expectations, we also observed a 6% increase in herbivory under ALAN. Our results highlight the importance of open experimental field studies in determining community-level effects of ALAN.