Light pollution impairs urban nocturnal pollinators

In urban centers, are pollinators plagued by night lights? And what problems can they create?

by Lorenzo Ciotti
Light pollution impairs urban nocturnal pollinators

In general, pollinating insects have morphological characters suitable for their specialization: the most common are the body thickly covered with bristles and the sucking or licking-sucking mouthparts. The first character means that the pollen remains trapped between the bristles and can thus be transported from flower to flower; the second is an adaptation to the diet of these insects, based on sugary liquids, represented in particular by the nectar of flowers.

Some insects have more marked specializations. For example, in the Apoidea, the tibiae of the hind legs are dilated and have an external concavity, called cestella, in which the collected pollen accumulates and held in a globular mass by bristles arranged along the edge of the cestella.

Another organ present in the Apoidea is the brush, a formation of sturdy bristles on the rear legs, which the insect uses to brush the body and collect pollen. In urban centers, are pollinators plagued by night lights? And what problems can they create? The study: Light pollution impairs urban nocturnal pollinators but less so in areas with high tree cover, published on the Science of the total environment, explained: We can read: "The increase in artificial light at night (ALAN) is widely considered as a major driver for the worldwide decline of nocturnal pollinators such as moths.

However, the relationship between light and trees as 'islands of shade' within urban areas has not yet been fully understood. Here, we studied (1) the effects of three landscape variables, i.e. sources of ALAN (mercury vapour/LED street lamps; overall light pollution), impervious surfaces (e.g.

roads, parking lots and buildings), and tree cover on species richness and abundance of two major macro-moth families (Noctuidae and Geometridae) and (2) the potential mitigating effect of trees on macro-moths attracted to ALAN.

We undertook a landscape-scale study on 22 open green areas along an urban-rural gradient within Berlin, Germany, using light traps to collect moths. Macro-moths were identified to species level and GLMMs applied with the three landscape variables at different scales (100 m, 500 m and 1000 m).

We found a significant negative effect of mercury vapour street lamps on macro-moth species richness, while impervious surfaces showed significant negative effects on abundance (total and Geometridae). We further found significant positive effects of tree cover density on species richness and abundance (total and Geometridae).

Effects of tree cover, however, were mostly driven by one site. LED lamps showed no predictive effects. A negative effect of ALAN (MV lamps and overall light) on macro-moths was most prominent in areas with low tree coverage, indicating a mitigating effect of trees on ALAN.

We conclude that mercury vapour street lamps should be replaced by ecologically more neutral ALAN, and that in lit and open areas trees could be planted to mitigate the negative effect of ALAN on nocturnal pollinators. In addition, sources of ALAN should be carefully managed, using movement detection technology and other means to ensure that light is only produced when necessary."