Observations on development of the gonad and on reproduction in Aphelenchus avenae

Nuclear changes occurring in male and female gonads of Aphelenchus avenae during postembryogenesis were studied in relation to time and feeding periods on Rhizoetonia solani. Development of the female gonad was similar to that in other nematode species, but development of the male gonad followed the growth pattern of female rather than male gonads. This deviation was explained by the assumption that males in antphimictic populations have appeared as the resnlt of recent evolntion of such populations to sexuality from originally parthenogenctic ancestors. A certain, period of feeding of larvae (16 h for L-2 and L-3, but 12 h for L-4) was required before molting. Cell divisions were confined to the periods of lethargus during the second and third molts, but started during the larval stage in fourth-stage larvae. Crosses in various combinations demonstrated that temperature-induced males do inseminate fentales of the amphimictic and some parthenogenetic populations, but their spermatozoa are nonfunctional. Similarly, males of the amphimictic population inseminated females of a parthenogenetic population, but the sperm did not penetrate the oocytes.