Moths are less attracted to light than they used to be -- Part 2
(continuing discussion of the Battles et al. journal article)
In 25 years of monitoring in Delaware starting in 1998, light-trap catch averages declined from about half as many moths as pheromone traps in the first 5 years to less than 5% as many moths by the end of the period. A similar pattern was observed over a shorter 10-year period of sampling in New Jersey. On the other hand, a 15-year period of sampling in Minnesota showed no difference in the efficacy of the two trapping methods.
The causes of this decline in light trap efficacy are uncertain. Competition from light sources in the area is one possibility, but the data on competing light sources is poor and no statistically significant results are found. The researchers speculate that the more likely cause is that rapid evolution has decreased the flight-to-light response of this species. The paper notes that the Corn Earworm seems particularly susceptible to rapid evolutionary change as it has multiple generations per year and high dispersal rates: it cannot survive winter temperatures in Canada and the northern US and migrates each spring from the southern US.
Overall, this is not good news for moth observers. Perhaps other means of trapping may need to be explored, such as bait, pheromones or suction traps. On the other hand, it remains to be seen whether this finding is applicable to other species as well.
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Are the moth population also declining?
It used to be that light pollution was more of an urban phenomenon, but increasingly rural property owners seem to feel a need to light up their properties at night. In rural Ontario monster homes are going up with an array of lights under the eves completely encircling the house. These "vanity lights" have become ubiquitous. Not to mention spotlights directed around the property. I could certainly see this driving evolutionary trends away from light attraction.
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