Light is the most important Zeitgeber for temporal synchronization in
nature. Artificial light at night (ALAN) disrupts the natural light-dark
rhythmicity and thus negatively affects animal behavior. However, to date,
ALAN research has been mostly conducted under laboratory conditions in
this context. Here, we used the field cricket, Gryllus bimaculatus, to
investigate the effect of ALAN on insect behavior under semi-natural
conditions, i.e., under shaded natural lighting conditions, natural
temperature and soundscape. Male crickets were placed individually in
outdoor enclosures and exposed to ALAN conditions ranging from
<0.01 to 1500 lx intensity. The crickets' stridulation
behavior was recorded for 14 consecutive days and nights and their daily
activity patterns were analysed. ALAN impaired the crickets'
stridulation rhythm, evoking a change in the crickets' naturally
synchronized daily activity period. This was manifested by a
light-intensity-dependent increase in the proportion of insects
demonstrating an intrinsic circadian rhythm (free-run behavior). This also
resulted in a change in the population's median activity cycle
period. These ALAN-induced effects occurred despite the crickets'
exposure to almost natural conditions. Our findings provide further
validity to our previous studies on ALAN conducted under lab conditions
and establish the deleterious impacts of ALAN on animal behavioral
patterns.