Spectral sensitivity of insect visual system is one of the most important functions that are useful for controlling potential pests. After briefly summarizing the basic structure of two typical compound eye types, the apposition type of diurnal insects and the superposition type of nocturnal insects, we will introduce the mechanisms underlying the spectral sensitivity of insect photoreceptors. We will then explain some technical aspects that are crucial for measuring spectral sensitivities.
To understand the visual responses of the southern green stink bug, Nezara viridula, we investigated the behavioral preference for wavelengths, and also checked the spectral sensitivity of the bug. The compound eyes of N. viridula adults showed a bimodal sensitive pattern to wavelengths (300–740 nm), responding strongly to ultraviolet region (peak at 360 nm), and maximally to green region (peak at 520 nm). In free-flying preference experiments using light-emitting diodes (LEDs) of five different peak wavelengths (373, 444, 464, 534 and 583 nm), both male and female adults strongly preferred the ultraviolet light (373 nm) among five LEDs. Among all other four, adults preferred blue region light (444 nm and 464 nm) to 534 nm and 583 nm. In dual choice experiment, N. viridula choose green light (534 nm) more than orange light (583 nm). These results show that N. viridula prefer shorter wavelength light under the same photon flux density, and indicate the potential use of short wavelength light for light trap to monitor N. viridula.
The attraction of the melon thrips, Thrips palmi Karny, to two types of traps combined with a colored sticky board and an LED array was investigated in 2010 in an eggplant greenhouse. The colors of the sticky boards were blue, yellow and white, and the peak wavelengths of the LED arrays were 470 nm (blue) and 375 nm (ultraviolet). The “direct type” of traps was designed to directly illuminate the plants with an LED array and set along the upper edge of the board whose sticky surface was directed to the plants. In the “reflective type” of traps, the LED array was set close to the plants and directed toward the sticky boards. As a result, the number of adult thrips caught was significantly larger in the reflective type of trap with combination of the blue sticky board and the blue LED.
We examined phototactic responses of dipteran insects, including Neoempheria ferruginea (Brunetti), Sciaridae, and Drosophila, using ultraviolet (365 nm), green (525 nm), and white wavelengths of a LED (light emitting diode) using a water-pan trap. The number of N. ferruginea captured (trap catches) were highest in the trap with ultraviolet LED. Then, we examined the effects of ultraviolet LED and surfactant (1% Tween 80) in the water-pan trap on the trap catches using generalized linear mixed model. Both ultraviolet LED and surfactant were shown to affect positively on the trap catches. Nevertheless, the LED variable had the highest effect on N. ferruginea trap catches. On the other hand, trap catches of Sciaridae and Drosophila were affected most by the surfactant.
Open field test (OFT) is a widely used procedure for the analysis of animal behaviors. However, a few studies using this method have been reported in insects. We here attempted to analyze a phototactic behavior of the brown-winged green bug, Plautia stali (Scott) by OFT, and to evaluate the effectiveness and utility of this approach. Bugs were released at the center of open field arena then illuminated with a light emission diode (LED). Their phototactic behavior was recorded by an infrared camera then two-dimensional trajectory analysis was performed for the video sequences. As a result, the OFT characterized an orientation pattern and walking speed of bugs approaching a light. We conclude that the OFT is an advantageous approach for the close examination of phototactic process and considering the ecological significances in insects.
To confirm inheritance of wing form and reproductive diapause of female Thrips nigropilosus, and prevalence of brachypterous and diapausing females in winter populations on the Ryukyu Islands, field sampling and rearing trials at 18°C were conducted. Kainan-shi (34.2°N) females from Honshu Island developing under short-day photoperiods (≤11.5 hours light) entered reproductive diapause, whereas Miyakojima-shi (24.1°N) and Yaese-cho (26.1°N) females from the Ryukyu Islands never entered diapause even under shorter day lengths. All Kainan-shi females molted into brachypters under short-day conditions (≤11 hours light) and became macropters under long-day conditions (≥12 hours light). The percentage of brachypters in Yaese-cho and Miyakojima-shi females developing under short-day conditions (≤11 hours light) was less than 50%, and no females developed into brachypters under photoperiods with at least 11.5 hours of light. Under short-day conditions (10 hours light), 93% of females molted into brachypters and 35% of females entered diapause in F1 hybrids between Yaese-cho females and Kainan-shi males. Macropters and brachypters were found in the field in overwintering adult females on Okinawa Island.
We analyzed part of the sodium channel gene to clarify the molecular mechanism involved in the pyrethroid resistance of the yellow tea thrips (Scirtothrips dorsalis), and found two amino acid mutations (T929I and L1014F) known as pyrethroid-resistant factors in several other insects. The L1014F mutation was shared with all the tested thrips from a field colony. On the other hand, the T929I mutation was found only in individuals which survived in pyrethroid treatment of agriculturally recommended concentration. This might suggest that pyrethroid resistance of S. dorsalis in the field is conferred by both mutations. We developed the PCR-RFLP assay using MboI to distinguish pyrethroid-resistant individuals.