In both Frankliniella fusca (Hinds) and Haplothrips verbasci (Osborn) the male reproductive system consists of 2 single-follicled testes, 2 vasa deferentia each enlarged at its posterior end into a seminal vesicle, one (F. fusca) or 2 (H. verbasci) pairs of accessory glands, an unpaired ejaculatory duct, and an extrusible phallus contained within a genital chamber above the 9th sternum.

Each testis of F. fusca contains only a single cyst of germ cells, while that of H. verbasci contains many. The spermatozoa of adult F. fusca are randomly distributed in each testis, whereas those of H. verbasci adhere together in longitudinally-disposed sperm bundles.

In both species the phallus consists of a sclerotized phallobase, bearing laterally a pair of parameres and produced caudad as a sclerotized (H. verbasci) or membranous (F. fusca) phallotheca. A protrusible vesicle, the endotheca, is continuous with the posterior margin of the phallotheca and is invaginated within it when the phallus is not in use. A sclerotized aedeagus is fused to the apex of the endotheca and is the posterior terminus for the intraphallic part (= ductus conjunctus) of the ejaculatory duct.

The postembryonic development of these structures and their musculature is described and is compared between the 2 species and with that occurring in other insects.

Meiosis is aberrant in both insects, and is probably correlated with the parthenogenetic development of the male larvae from unfertilized eggs. The first maturation division seems to be mitotic, while the second is reduced to the ejection of a nucleate polar body from each of the secondary spermatocytes.

Theoretical implications of the observations are discussed and hypotheses are proposed to explain the formation of the spermatophore and the mechanism of its transfer by the male of F. fusca.