CRY1 is involved in the take-off behaviour of migratory Cnaphalocrocis medinalis individuals

Abstract

Background: Numerous insect species undertake long-distance migrations on an enormous scale, with great implications for ecosystems. Given that take-off is the point where it all starts, whether and how the external light and internal circadian rhythm are involved in regulating the take-off behaviour remains largely unknown. Herein, we explore this issue in a migratory pest, Cnaphalocrocis medinalis, via behavioural observations and RNAi experiments.

Results: The results showed that C. medinalis moths took off under conditions where the light intensity gradually weakened to 0.1 lx during the afternoon or evening, and the take-off proportions under full spectrum or blue light were significantly higher than that under red and green light. The ultraviolet-A/blue light-sensitive type 1 cryptochrome gene (Cmedcry1) was significantly higher in take-off moths than that of non-take-off moths. In contrast, the expression of the light-insensitive CRY2 (Cmedcry2) and circadian genes (Cmedtim and Cmedper) showed no significant differences. After silencing Cmedcry1, the take-off proportion significantly decreased. Thus, Cmedcry1 is involved in the decrease in light intensity induced take-off behaviour in C. medinalis.

Conclusions: This study can help further explain the molecular mechanisms behind insect migration, especially light perception and signal transmission during take-off phases.

Keywords: Cnaphalocrocis medinalis; Cryptochrome; Light intensity; Migratory insect; Take-off behaviour.

Fig. 1

Take-off behaviour of field populations at different time periods under field conditions (A) and laboratory simulated environments (B) and laboratory populations at different time periods (C) and light intensities (D). Red lines with circles mean light intensity in different time periods, and the data are presented as average SEM. During the non-treatment time period, the photoperiod was set according to the conditions when C. medinalis was reared, that is, 5:30–19:30 was the light period

Fig. 2

The relative expression levels of Cmedcry1, Cmedcry2, Cmedtim and Cmedper in take-off and non-take-off individuals. The long horizontal lines represent the means, the upper and lower lines represent the average SEM, and * indicating significant differences (t-test—P < 0.05), while ‘ns’ indicates non-significant differences

Fig. 3

Take-off proportion (A) and the relative expression of Cmedcry1, Cmedcry2, Cmedtim and Cmedper under full-spectrum, blue, green and red light (B). The circles represent the individual measured values of the samples, the long horizontal lines represent the means, the upper and lower lines represent the average standard error of the mean and significant differences in take-off proportion (chi-squared test—P < 0.05) and relative expression levels (Tukey’s HSD—P < 0.05) were observed among different letters

Fig. 4

Take-off proportion (A) and RNAi efficiency (B) of C. medinalis after interference with Cmedcry1 expression and relative expression of Cmedcry2, Cmedtim and Cmedper under full-spectrum and blue light (B). The circles represent the individual measured values of the samples, the long horizontal lines represent the means, the upper and lower lines represent the average standard error of the mean and * indicates significant differences in the take-off proportion (chi-squared test—P < 0.05) and relative gene expression (t-test—P < 0.05) among the dsGFP and dsCRY treatment groups, while ‘ns’ indicates non-significant differences