Abstract. The degree of polyandry in a species is linked to other life history traits such as egg maturation, life span, and male ejaculate size and quality. The study of differences in mating strategies between closely related species can provide a better understanding of the evolution of these strategies and of sperm competition. Mating patterns of two closely related species of small ermine moths (Yponomeuta) were investigated in the laboratory. The average female age at first mating was higher in Y. cagnagellus than in Y. padellus. Both species mated more than once; however, Y. cagnagellus females were more likely to remate in a short time frame. Moreover, Y. cagnagellus had higher life time female mating frequencies than Y. padellus (viz., 3.0 versus 2.0). These differences in mating frequency were confirmed in the field by examining the presence of spermatophores (or their remains) in the bursa as well as sperm in the spermatheca of field-caught females.

According to sympatric speciation theory, adaptation to different host plants is expected to pleiotropically lead to assortative mating, an important factor in the reduction of gene flow between the diverging subpopulations. This scenario predicts mating on and oviposition preference for the respective hosts in both the diverging subpopulations and recently originated species. Here, we test both predictions in the oligophagous Yponomeuta padellus (L.) and the monophagous Yponomeuta cagnagellus (Hübner) (Lepidoptera: Yponomeutidae), two closely related small ermine moth species from the western European clade of Yponomeuta for which speciation in sympatry has been proposed. Mating location and adult host acceptance were evaluated under both semi-field (in a large outdoor cage with a choice of host and non-host plants) and field conditions. In the semi-field experiment, only Y. cagnagellus showed some preference for mating on its own host (16% of all mating pairs) over non-host plants (3% of all mating pairs). However, in both species, more than 80% of the mating pairs were not formed on a plant but instead on the cage itself. Further examination of the mating site of Y. cagnagellus in the field revealed no preference for host plants over non-host plants in the two consecutive years of observation. Yponomeuta padellus females, collected from and reared on Prunus spinosa L. (Rosaceae), showed an oviposition preference for the alternative host Crataegus monogyna Jacq. (Rosaceae) in the semi-field experiment. We thus found no evidence that host-plant fidelity (in terms of mating site) has been the driving force in the speciation process of these Yponomeuta species, nor did we find evidence of host race formation in the tested population of the oligophagous Y. padellus .

Theory predicts that in monandrous butterfly species males should not invest in a long lifespan because receptive females quickly disappear from the mating population. In polyandrous species, however, it pays for males to invest in longevity, which increases the number of mating opportunities and thus reproductive fitness. We tested an extension of this idea and compared male and female lifespan of two closely related Yponomeuta species with different degree of polyandry. Our results confirmed the theoretical prediction that male lifespan is fine-tuned to female receptive lifespan; once-mated males and females of both polyandrous species had an equal lifespan. However, the degree of polyandry was not reflected in male relative to female lifespan. The observed similar female and male lifespan could largely be attributed to a dramatic reduction of female lifespan after mating.

Nine microsatellite primers were developed for Yponomeuta padellus (Lepidoptera: Yponomeutidae) and tested for their applicability in analysing genetic population structure. Eight of the nine loci were highly polymorphic with on average 11.4 alleles. Crossspecies amplification of the nine primer pairs was tested in five other moth species. Primer pairs amplified in Y. cagnagellus , Y. malinellus , Y. evonymellus , and Y. rorellus but not in Y. sedellus and Plutella xylostella.