Phototactic behavioral response of agricultural insects and stored-product insects to light-emitting diodes (LEDs)

Agricultural insects and stored-product insects are influenced by luminance intensities, exposure times, and wavelengths of light-emitting diodes (LEDs). Based on the phototactic behaviors of the agricultural insects, green or blue LEDs are most attractive for Bemisia tabaci, Trialeurodes vaporariorum, Myzus persicae, Liriomyza trifolii, Spodoptera exigua, and Spodoptera litura. Green LED attracts Plutella xylostella and Frankliniella occidentalis. Similarly, green or blue LEDs are more attractive to agricultural insects, such as Liriomyza sativae, Sogatella furcifera, and Nilaparvata lugens, than other wavelength LEDs. Concerning the phototactic behaviors of the stored-product insects, red LED is attractive for, in descending order Tribolium castaneum, Sitophilus zeamais, Lasioderma serricorne, and Tyrophagus putrescentiae. Blue LED captures most Sitophilus oryzae and Sitotroga cerealella. Red and blue LEDs are more attractive for stored-product insect pests rate than ultraviolet LED and green, yellow, white, and infrared LEDs. Based on the attraction rate of the stored-product insects on granary, red LED is most attractive for S. cerealella and Plodia interpunctella. These light sources are effective in controlling agricultural and stored-product insects. Applying LED technology for greenhouses and granaries along with conventional traps reduces crop loss due to moths, beetles, aphids, and weevils. LEDs have potential value in integrated pest management.


Introduction
Many countries are using synthetic insecticides as the primary means of controlling insect pests [1,2]. However, repeated use of synthetic insecticides can increase the development of resistance in the insect pests and has negative effects on the environment and nontarget insects [2,3]. Efforts are ongoing to develop sustainable alternative and eco-friendly methods, such as the use of electric traps, food traps, and natural insecticides [1][2][3][4].
Phototaxis is the behavior of insect species in response to light sources. This movement is influenced by the light wavelength, and the quality and intensity of the light source [5]. In general, insect pests can perceive light ranging in wavelength from 350 to 700 nm and respond in diverse ways [6]. The alternative techniques being developed include phototaxis; electric traps equipped with black and incandescent light bulbs are used for surveillance, for example. The incandescent bulb as the standard light commonly used in light traps ranges in wavelength from 350 to 700 nm with a maximum output wavelength at 700 nm [7]. Insect species can be attracted or repelled to special light sources, such as artificial lights [8]. Certain insect species exhibit a directional response to light-emitting sources including high-or low-intensity light [9]. The use of artificial light sources in integrated pest management (IPM) has increased globally [10]. Light-emitting diodes (LEDs) have emerged as an important technology in the development of agricultural systems [11,12]. The many advantages of LEDs include the eco-friendly technology, functional improvement, plant growth, high luminous efficiency, selectivity of specific wavelength and light intensity, low weight, low electronic consumption, small size, prolonged lifetime, and environmental affinity [13,14].
LED traps may be a potential alternative to commercial traps for mass trapping and phototactic monitoring of insect pests. Specific wavelength LED sources are being used for monitoring as well as trapping [7,15]. Pest insects will move toward light lamps or other illuminations in outdoor settings [16]. This phototactic behavior of pest insects is the basis of the design of electronic insect traps [16]. The light traps are equipped with LED sources; they effectively attract agricultural and stored grain insect pests including aphids, beetles, moths, and weevils and prevent the entry of these insects into greenhouses and granaries [17,18]. Interest is growing in control technology that exploits insect behaviors to light sources as an alternative to synthetic insecticides [16,19]. Here, we review the advanced control technologies of insect species that employ new light sources including LEDs.

Classification of phototactic behavioral responses to light sources of various insects
Insect behavior to light is varied and can be categorized [20]. The typical behavior is phototaxis. Insects display several phototactic responses including attraction (movement toward the light source: positive phototaxis) and repulsion (movement away from the light source: negative phototaxis). Optimal conditions, which include effective  wavelengths, exposure time, and intensities to light source, are diverse among insect species [21,22]. Negative phototaxis could be useful to prevent entrance of pest insects to greenhouses and granaries [23,24]. Behavioral responses to light by insect species also include light adaptation, circadian periodicity, photoperiodism, and light toxicity [20]. Nocturnal insects can adapt to light sources; typical adaptive behaviors are diminished migration, settling near the light source, and mating [20]. Circadian periodicity is daily behavioral response that encompasses courtship, feeding, flight, and locomotion [25]. Artificial light at night can change the diurnal or nocturnal responses and timing of insect species [26], which represents a phase shift in chronobiology [27]. Photoperiodism is the physiological behavior of insect species to light, such as day light. The start of resting can be prevented by repeatedly exposing insects to light sources for some days [28]. Insects that do not enter diapause cannot overwinter. Continuous light irradiation is structurally damaging and causes light toxicity [29]. Photo-irradiation is also useful for treatment of crops before the post-harvest in the greenhouse and granary settings. Insect behaviors to light sources are significantly influenced by various factors of the light, such as intensity, single or combined wavelengths, exposure time, and differences of light intensity and color to those of ambient lighting [19,30]. In the remainder of this minireview, we discuss the technologies being currently being used to control many insect species.
Study on physical control of insect pests by using light sources The influence of LEDs on insect color and light perception with different wavelengths and on behavior, and the development of control technology involving new light sources has been described [19]. Physiological systems have been comprehensively utilized to measure the influence on many insect species in a wide range of wavelengths [51]. Phototactic responses of many insect species to LED sources have been investigated to clarify the relationship between insect behaviors and light wavelengths, with the goal of determining the effective attractant and repellent wavelengths for target insect pests [51]. The development of LED sources that are able to be used instead of incandescent light traps is an ongoing research interest. In addition, wavelengths of light that effectively attract parasitoids, which are natural enemies of insect pests, are being investigated [19].
In conclusion, LED equipment with various wavelengths can now be manufactured due to current technological advances, and new agricultural technology using light is starting to attract attention. Advances are also expected in the use of light for insect control as the results of these technological developments in lighting. Based on the new research being conducted by National Agricultural Research Organisation, we hope to ensure the further development of agricultural technology founded on a good balance of input from basic study in universities and independent administrative institutions and applied technology from private companies and public research institutes to establish the next generation of pest control technology.