Effects of the range of light wavelengths on the phototactic behaviour and biological traits in the melon thrips,Thrips palmi Karny (Thysanoptera Thripidae)

Effects of different wavelengths of silicon-based LED on the growth, development, and reproduction of Spodoptera frugiperda (Lepidoptera: Noctuoidea)

Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), or fall armyworm (FAW), is a well-known pest that causes serious harm to agricultural output. However, there is a lack of reports on the impacts of different wavelengths of silicon-based LED lights on its population dynamics and age-stage two-sex life table. This study aims to form an age-stage two-sex life table to evaluate the effects of nighttime LED light with 4 different wavelengths (red [630 ± 2.5 nm], yellow [568 ± 2.5 nm], blue [460 ± 2.5 nm], and green [535 ± 2.5 nm]) on FAW growth, development, and fecundity. The results revealed that the survival rate of pupae was the lowest under blue light treatment. Blue and green light therapy dramatically reduced the fecundity of FAW, and exposure to green light increased the adult preoviposition period (APOP), the total preoviposition period (TPOP), and the longevity of the adult. Moreover, among the 4 different wavelengths of light, the net reproductive rate (R0), intrinsic rate of increase (r), and finite rate of increase (λ) of FAW were the greatest under red light and significantly decreased under green and blue light, the longest mean generation time (T) occurred under green light. Our results suggest that blue and green light are beneficial for preventing and controlling FAW. These findings may help provide new pest control strategies to improve pest control and reduce agricultural economic losses.

Colour vision in thrips (Thysanoptera)

Insects are an astonishingly successful and diverse group, occupying the gamut of habitats and lifestyle niches. They represent the vast majority of described species and total terrestrial animal biomass on the planet. Their success is in part owed to their sophisticated visual systems, including colour vision, which drive a variety of complex behaviours. However, the majority of research on insect vision has focused on only a few model organisms including flies, honeybees and butterflies. Especially understudied are phytophagous insects, such as diminutive thrips (Thysanoptera), in spite of their damage to agriculture. Thrips display robust yet variable colour-specific responses despite their miniaturized eyes, but little is known about the physiological and ecological basis of their visual systems. Here, we review the known visual behavioural information about thrips and the few physiological studies regarding their eyes. Eye structure, spectral sensitivity, opsin genes and the presence of putative colour filters in certain ommatidia strongly imply dynamic visual capabilities. Finally, we discuss the major gaps in knowledge that remain for a better understanding of the visual system of thrips and why bridging these gaps is important for expanding new possibilities for applied pest management strategies for these tiny insects. This article is part of the theme issue 'Understanding colour vision: molecular, physiological, neuronal and behavioural studies in arthropods'.

Phototactic Behavioral Response of the Ectoparasitoid Beetle Dastarcus helophoroides (Coleoptera: Bothrideridae): Evidence for Attraction by Near-Infrared Light

The ectoparasitoid beetle, Dastarcus helophoroides (Fairmaire) (Coleoptera: Bothrideridae), has been widely used as a biological control agent for many cerambycid beetles in China, Korea, and Japan. However, much less is known about its phototactic behavior to visual stimuli. In this paper, the phototactic behavioral response of D. helophoroides to 27 monochromatic lights and to nine illumination intensities of the most attractive light was evaluated using light-emitting diodes (LEDs) as light sources. The results showed that in dual choice between darkness and individual LED light, D. helophoroides adults exhibited a positively phototactic response to all wavelengths ranging from 300 to 860 nm. The near-infrared light (NIR, ranging from 700 to 760 nm) elicited stronger phototactic behavioral response, showing a preference for NIR wavelengths light. In paired choice among four preferred NIR lights, D. helophoroides adults displayed a significantly more favorable response to NIR light at 700 nm. Furthermore, the beetles expressed varying levels of sensitivity to illumination intensities from 1 to 600 lux under NIR light at 700 nm. The phototactic response was strongest at 7 lux and a statistically significant downward trend was found with increasing or decreasing the illumination intensities. These findings clearly demonstrate that D. helophoroides is a positively phototactic insect and its phototactic behavior is significantly influenced by light wavelength and illumination intensity, among which NIR light with peak wavelength at 700 nm and an intensity at 7 lux are most suitable in attracting D. helophoroides adults.

Synergistic Effects of the Red Light and Blue Traps on Control of Thrips palmi (Thysanoptera: Thripidae)

The melon thrips (Thrips palmi) is a serious insect pest of vegetables and ornamental plants. To control and monitor this thrips, blue traps are widely used. We previously reported that irradiation of cucumber plants with red light-emitting diodes (660 nm) causes T. palmi to avoid the plants. Here, we evaluated the responses of T. palmi adults to a cucumber plant in an experimental arena with either a transparent sticky trap or a blue sticky trap, without or with illumination by a red LED panel. When T. palmi were introduced into the arena, the number of thrips attracted to the plant was lowest in treatments using the red light and blue trap. On the other hand, when T. palmi were inoculated on plants first, most thrips stayed put on the plants. Placing both red LEDs and blue sticky traps in greenhouses before the thrips invade the greenhouse from the outside might effectively control T. palmi.

Deterioration of World Heritage Cave Monument of Ajanta, India: Insights to Important Biological Agents and Environment Friendly Solutions

Heritage monuments across the world are affected by a variety of physical and biological stresses. Damage to heritage monuments due to insects and pests is growing with increasing anthropogenic pressure and changing climatic conditions. Cave monuments are habitats to microbes, algae, fungi, and insects, and are unique biodiversity sites due to their low temperature, little to no sunlight, and high moisture conditions. This study takes stock of available information on important factors that facilitate the growth of insect pests and degrade heritage monuments. Ajanta Caves, a UNESCO world heritage site in India, is a human marvel, important archaeological and heritage site of immense cultural and historic values. The present paper is an attempt to understand a variety of stresses and factors with a focus on insect pests that have substantially affected Ajanta cave paintings in the last few decades. The study also provides information on available approaches for damage control including the need for an integrated insect pest management for protecting cave monuments against rapid degradation across the country in general and Ajanta caves in particular. A light-based approach is the key highlight of the study that can be used as an effective and efficient approach to protect archaeological sites especially cave paintings from insect pests without disturbing the pollinator diversity and surrounding environment.