Trapping efficiency and sex ratio of Maladera matrida beetles in yellow and black traps

In field experiments, which started several years ago to investigate the means of chemical communication of the Maladera matrida beetle, we found that the ratio of males to females attracted to the bait (live females with food) was 3:2-5:4 (60:40-55:45). These findings suggested that an aggregation pheromone is involved in the chemical communication, but the constant small preference for attracted males raised the question whether the active compound(s) is indeed an aggregation pheromone or whether it is a sex pheromone released by the female to attract the male. Since the traps used in our field studies were made of yellow plastic, we had to consider the possibility that the yellow color could have influenced the trapping of the flying beetles and biased the findings for the behavior and mode of attraction toward the source of the chemical communication. To clarify this point, we set out, in this study, to conduct field experiments in which we compared the standard yellow traps with black traps. We found that the bright yellow color did indeed affect the results for chemical communication: The total catch in the yellow traps was double that in black traps, and the male-female ratio in the black traps increased to 4: 1(80:20). This result hints that a sex pheromone, and probably not an aggregation pheromone, as previously thought, is involved in the chemical communication of the M. maladera beetle.