Madagascar periwinkle is a perennial plant that readily establishes itself in tropical and subtropical areas to which it is introduced.  Flowers are visited by a wide variety of insects, including butterflies, bees, flies, and beetles, but only butterflies or moths are likely to serve as pollinators, as the floral structure is adapted to pollination by a long-tongued insect (Albers and van der Maesen, 1994).  Unlike most species in its family, Madagascar periwinkle is self-compatible; however, self-pollination under normal conditions may be relatively uncommon.  Intraflower self-pollination usually does not occur because of the physical separation between the stigma and anthers, but three distinct genetic variants have been identified that have elongated ovaries or styles and thus do demonstrate intraflower self-pollination (Kulkarni et al. 2005). 

References

Albers, P. and L. J. G. van der Maesen. 1994. Pollination of Apocynaceae.  Wageningen Agric. Univ. Papers 94-3: 61-81.

Kulkarni, R. N., Y. Sreevalli and K. Baskaran. 2005. Allelic differences at two loci govern different mechanisms of intraflower self-pollination in self-pollinating strains of periwinkle. J. Hered. 96: 71-77.

Sreevalli, Y., K. Baskaran, R. N. Kulkarni and S. Kumar. 2000. Further evidence for the absence of automatic and intra-flower self-pollination in periwinkle.  Curr. Sci. 79: 1648-1649.