Thripinae

Mound, Laurence A., 2009, Sternal pore plates (glandular areas) of male Thripidae (Thysanoptera), Zootaxa 2129, pp. 29-46 : 43

Thripinae females with sternal pore plates

Although sternal pore plates are primarily associated with Thysanoptera males, this sex-linkage is occasionally inverted, with male-like pore plates occurring on sternite III (more rarely III and IV) in females of several unrelated genera. Unfortunately, it is not known if the internal structure of pore plates is similar in males and females, thus it is not possible to be sure of their homology. Females of at least five species in the genus Oxythrips have a pore plate, and this is true also of the single species in the closely related genus Macrurothrips (zur Strassen, 2003), as well as those in the related genus Chilothrips ( Hoddle et al., 2008) . However, this is the only good example of the presence of these structures in females of species that are related phylogenetically. Females of Chaetanaphothrips signipennis , a widespread pest of bananas, consistently have a transverse pore plate ( Fig. 27 ) on the third sternite, but this is not found in any of the other 19 species in the genus. Cyrilthrips, a related monotypic genus, also has a similar structure in females (Tree & Mound, 2009), but in the large and worldwide genus Thrips only one species, Thrips knoxi , is known to have females with a pore plate on sternite III ( Fig. 39 ). Even in this species, the pore plate is present or absent in different populations ( Mound & Masumoto, 2005). Similar inconsistency in this character state occurs in females of Frankliniella australis , one of very few species in this large genus that have females usually with a pair of pore plates on the third sternite ( Fig. 26 ). Females of Limothrips cerealium , the most abundant thrips on grasses in Western Europe, typically have no pore plates, but in some populations in the Mediterranean region females have a pore plate on sternites III and IV ( Mound & Palmer, 1974).

Pore plates in females have not been demonstrated to have any functional significance, and they possibly represent some form of genetic aberration. Such inversion of a sex-linked character state has been reported occasionally amongst other Thysanoptera . For example, in the genus Machatothrips (Phlaeothripidae) with 14 described species from the Old World tropics, females but not males bear a row of tubercles on the inner margin of the fore femora. However, in two species of this genus from Malaysia males sometimes have similar although rather weak tubercles ( Palmer & Mound, 1978).

Figures

FIGURES 17 – 27. Sternal pore plates of male Thripinae 17 – 25: (17) Frankliniella occidentalis. (18) Frankliniella insularis. (19) Taeniothrips orionis. (20) Lomatothrips pinopsidis. (21) Parabaliothrips newmani. (22) Kakothrips pisivorus. (23) Pseudanaphothrips achaetus. (24) Pezothrips kellyanus. (25) Yoshinothrips pasekamui. Pore plates on sternite III of female Thripinae 26 – 27: (26) Frankliniella australis. (27) Chaetanaphothrips signipennis.

FIGURES 28 – 39. Sternal pore plates of male Thripinae 28 – 38: (28) Dichromothrips smithi. (29) Organothrips indicus. (30) Organothrips wrighti. (31) Tusothrips sumatrensis. (32) Limothrips cerealium. (33) Stenchaetothrips biformis. (34) Thrips hawaiiensis. (35) Fulmekiola serrata. (36) Microcephalothrips abdominalis. (37) Thrips australis. (38) Thrips atratus. (39) Sternite III of female Thrips knoxi.