Rare patterns of dorsal puncture in Pterostichus oblongopunctatus (Coleoptera: Carabidae)

BACKGROUND: The carabid beetle species Pterostichus oblongopunctatus is common in different types of forests in Poland and Europe. With respect to this species, some unclarities exist concerning the morphological feature of punctures on the elytra. P. oblongopunctatus has dorsal pits in the third interval of the elytra, the available identification keys, however, provide inconsistent information concerning the puncture in other intervals. During long-term studies at different study sites in Poland, the first author rarely but regularly discovered individuals with unusual dorsal puncture patterns, i.e., pits in the fifth and even in the seventh interval of the elytra. Since such rare patterns might be connected with special habitat characteristics, and thus have a potential as an indicator, the aim of the study was to test if they are connected with specific subpopulations (interaction groups), if they are related to the sex or size of the beetles, and if they are related to specific habitat conditions. MATERIAL AND METHODS: We counted the pits on the elytra, determined the sex, and measured the length of the right elytron of individuals of P. oblongopunctatus collected at numerous study sites located within the borders of the Regional Directory of National Forests in Piła (Western Poland) over the period 2014–2016. RESULTS: Altogether, 1,058 individuals of P. oblongopunctatus were subjected to statistical analysis. Almost 19% of the individuals had a dorsal puncture in the fifth interval of the elytra and about 0.7% had a dorsal puncture in the seventh interval of the elytra. In 2014 and 2015, significantly more females exhibited such unusual patterns of dorsal puncture than males. Even if not statistically significant, in 2016 also relatively more females showed such a pattern. Neither males nor females of the analysed individuals with usual puncture patterns showed a significant difference in the length of the right elytron from those with unusual puncture patterns, and neither for males nor for females a significant correlation of the percentage share of the individuals with unusual puncture patterns with the age of the study sites could be detected. However, both males and females with unusual patterns had more dorsal pits than those without. Moreover, males as well as females showed in all those years a trend that the individuals with unusual patterns have more pits in the third interval of the elytra. DISCUSSION: The results indicate that females are more likely to exhibit unusual patterns. Since individuals of P. oblongopunctatus with a higher number of pits on the elytra are supposed to prevail in more wet habitats, such patterns might be related to moisture conditions. The possibility of pits in the seventh interval of the elytra should be added to identification keys.