Abstract
The pine bark bug Aradus cinnamomeus is a Eurasian insect pest of Scots pine. Each generation lives for two years in most areas in Europe, but in the north and in the Aland archipelago the generation time is three years. In western Finland, the 2-year bugs reproduce mainly in odd years, while in eastern Finland (as well as in eastern Sweden) the even-year generation predominates. Odd-year bugs are very rarely found in the even-year area, and even-year bugs are very rarely found within the odd-year area. The existence of sympatric but isolated alternate-year generations offers a possibility to study the effect of ecological genetic factors in a natural test situation since all environmental variables should be otherwise identical. In the north and in the Aland archipelago, the preponderance of one generation is not so pronounced, and three generations usually coexist in almost equal numbers. The Finnish parapatric odd and even-year generations (which are in the majority) are genetically virtually identical, while the odd and even-year minority generations deviate genetically (and morphologically) from the majority ones. In the three-year area the sympatric but allochronic bug generations differ genetically from each other to about the same extent as the allopatric but synchronic populations differ from each other. The sympatric differentiation can be explained as being a result of within species competition, although several other possible explanations exist. Furthermore, the two-year bugs collected from eastern Sweden appeared to diverge genetically, although they represent the locally predominating generation.
Highlights
T h e Finnish parapatric odd and even-year generations are genetically virtually identical. while the odd and wen-year minority generations deviate genetically from the majority ones
The life cycle of this hcmimetabolous insect takes individuals can be found within the even-year gentwo years, with two obligatory hibernations in most eration of eastern Finland; respectively, very few parts of Europe including southern Finland
Samples taken in Kerava (KER2) and Jyviskyla (JYV2) are exceptional since they belong to the eastern even-year generation, but differ genetically from the other majority samples from eastern Finland
Summary
1 9 8 7 . 1 9 9 0 . 1 8 8 3... 1 9 8 5 , 1 9 8 8 . 1 Q Q l. -Bug samples taken from differminority and majority generations both in the east ent sites were subjected to routine starch gel elecand west. Before this study, it was not definitely trophoresis and enzyme assays. The genetic distances between bugs from separated majority generations really belonged to different localities were calculated, on the basis of the same species. Among majority generations evoked several ques- The distances are shown in the form of a UPGMA tions Where these dissenters evolutionary units of dendrogram. Owing possible reciprocal effects of temporally isolated to the low variation, the distances shown in the bugs on each other. 70 % of the samples belonged t o the six lowest branches of the UPGMA dendrogram, deviating from each other by a genetic distance of less than
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