Copulatory behavior of predacious ladybird Harmonia axyridis (Coleoptera: Coccinellidae) under different illuminative conditions

Abstract

As one of the most important environmental factors, the light condition may influence the performance of development and physiological behavior in insect. The variation of light environment could induced many negative phenomenon, such as diapause, courtship inhibition and lower food consume. The intensive research on the light influences may promote the efficiency in massive rearing and population manipulation of the natural enemy. We focused on the key predacious natural enemy coccinellid Harmonia axyridis, which has been utilized as efficacious biological control agent to suppress various arthropod herbivores at present study to reveal the influences of light intensity, photoperiod and wavelength to the copulatory behavior and fertility by using an animal behavior automatic observation monitoring system. Totally 3 illuminative factors and 17 treatments, included light intensity (600 lx900 lx1200 lx1500 lx1800 lx ×2100 lx), photoperiod (light: dark=0:24, 6:18, 12:12, 18:6 and 24:0), and light wavelength (violet (395 nm), blue (480 nm), green (510 nm),yellow (75 nm), orange (610 nm) and red (685 nm)) were set as different environment conditions respectively. By reviewing the video records, the results showed that: (1) There are significant differences of each copulatory behavior and fertility between light and dark conditions of H. axyridis; (2) the courtship behavior was not influenced by light intensity but showed significant shorter in high intensity (in 1800 lx and 2100 lx) of copulation and interval duration that darker conditions (600 lx and 900 lx). We also did not find some significant influences by the variation of light intensity on pre-duration of mating. The offspring hatchability decreased with the increasing of light intensity although we did not find some differences of accumulation fecundity; (3) Long photoperiod and full day-light environment may enhance the courtship frequency. The ladybird couples showed significantly shorter pre-duration of mating in full-dark and short photoperiod conditions. The copulation and interval duration decreased with the prolonging of photoperiod but showed increasing in accumulated fecundity and offspring hatchability; (4) The light wavelength did not show significant influences to the courtship of male. Similarly, all couples in all colored conditions represented no different in pre-duration of mating. The mating duration and intervals duration decreased with the increasing of light wavelength. Both accumulative fecundity and larvae hatchability were showed significant highest in yellow (575 nm) and green (510 nm) conditions than rest colored treatments. The results of present study indicated the significant influences of light variation to the mating process in H. axyridis and it provided theoretical values for our continuous work on the environmental fitness and enhancement of plasticity adaption in biological control processes of H. axyridis. It indicated high illuminative intensity, long day-light photoperiod and in moderate colored (light wavelength) conditions could benefit the predacious ladybird H. axyridis in both massive rearing or in inoculative releasing via augmentative biological control application in greenhouse or other agroecosystem. Our study have provided the empirical witness of the value in light manipulation in insect conservation and augmentation system.