Insemination and fertilization in the seed bug Lygaeus simulans (Heteroptera : Lygaeidae)

In the laboratory, not all females of the seed bug Lygaeus simulans Deckert , 1985, produced fertilized eggs after copulation: 26.7% of the females wer e not inseminated and 5% were inseminated but did not lay fertilized eggs; only in 40% of the couples did copulation result in fertile eggs. The remai ning 28.3% of couples refrained from mating. Duration of copulation was ass ociated with insemination and fertilization: (i) fertile eggs were produced by only one couple that copulated for less than 60 min and all those that copulated for more than 360 min, (ii) probability of fertilization increase d steadily with duration of copulation between 60 and 360 min, and (iii) du ration of copulation was significantly different for couples that showed di fferent insemination status. A possible morphological explanation for this rime dependency was revealed by examining the genitalia of 69 couples freeze-fixed in copula after diffe rent periods in copulation. Because of the intricate structure of the genit alia in L. simulans, a male takes a long time to manoeuver its intromittent organ into the narrow insemination duct of the female. Only if completely inserted is the tip of the intromittent organ close enough for successful e jaculation of sperm into the spermatheca. The freeze-fixing experiment reve aled that it usually took the male more than 30 min to locate the entrance to the insemination duct and another 30 min for full penetration. This expl ains why copulations that lasted less than 60 min failed, since inseminatio n began only after intromission was complete. The experiments, therefore, indicated that there is a relationship between the complex morphology of the genitalia and the low rates of insemination a nd fertilization in L. simulans.