Reproductive Behavior of Echinothrips americanus (Thysanoptera: Thripidae).

Most Thysanoptera possess a haplo-diploid reproductive mode and reproduce via arrhenotoky. Females can mature eggs successively throughout almost their entire life, but in most terebrantian thrips spermiogenesis is complete by adult male eclosion, and testes contain only mature spermatids. In parasitoid wasps this phenomenon of preadult spermiogenesis is described as prospermatogeny. It is unclear if prospermatogeny and this predetermined sperm quantity have implications for mating strategy and fitness. In this study, we give a detailed description of mating behavior of the thripine species Echinothrips americanus, which largely corresponds with the only available data of another species of this family, Frankliniella occidentalis (Thysanoptera: Thripidae). With investigations using light microscopy, we describe for the first time the chronological sequence of internal processes during copulation. The release of male accessory gland material followed subsequently by spermatozoa indicates production of a female-determined type 1 spermatophore. Despite prospermatogeny, males are able to inseminate 10 females with an equal amount of spermatozoa. It is only the quantity of glandular material that decreases with the number of previous copulations. Based on these new findings, the reproductive strategy of this species is discussed.

Male reproductive system and spermatogenesis of Limodromus assimilis (Paykull 1790).

Based on advanced light and electron microscopy, we describe the male reproductive system and sperm development of Limodromus assimilis. The genital tract consists of pairs of uni-follicular testes, spermatic ducts with diverticula regions, seminal vesicles, accessory glands, an unpaired ejaculatory duct and an aedeagus containing an internal sac equipped with sclerotic scales. Based on their morphology, we draw conclusions about their functions. After spermatogenesis within the follicle, the spermatozoa become released from the sperm cysts. The single spermatozoa move into the diverticula of the vasa deferentia I. Here, they become attached to central rods (spermatostyles), forming secondary conjugates (spermiozeugmata). The coordinated flagella movement of the conjugates possibly improves sperm velocity. Using super-resolution microscopy, we identified highly condensed reticulate chromatin in the lancet-shaped spermatozoa heads and the mitochondrial derivates of the flagella, likely formed by genomic and mitochondrial DNA, respectively. The results show, for the first time, sperm bundle formation in a Platynini species mainly corresponding to that found in Pterostichini species.

Active aggregation among sexes in bean flower thrips (Megalurothrips sjostedti) on cowpea (Vigna unguiculata).

Male sexual aggregations are a common territorial, mating-related or resource-based, behaviour observed in diverse organisms, including insects such as thrips. The influence of factors such as plant substrate, time of day, and geographic location on aggregation of thrips is uncertain, therefore we monitored the dispersion of male and female bean flower thrips (BFT), Megalurothrips sjostedti (Trybom) (Thysanoptera: Thripidae), on cowpea, Vigna unguiculata (L.) Walp. (Fabaceae), over three cowpea growth stages and across three cowpea-growing areas of Kenya. Our results indicated that for all the crop growth stages, the density of BFTs varied over the time of day, with higher densities at 10:00, 13:00, and 16:00 hours than at 07:00 hours. Thrips densities did not differ among blocks at the budding stage, but they did at peak flowering and podding stages. Dispersion indices suggested that both male and female BFTs were aggregated. Active male aggregation occurred only on green plant parts and it varied across blocks, crop stages, and locations. Similarly, active female aggregation was observed in peak flowering and podding stages. Such active aggregation indicates a semiochemical or behaviour-mediated aggregation. Identification of such a semiochemical may offer new opportunities for refining monitoring and management strategies for BFT on cowpea, the most important grain legume in sub-Saharan Africa.

Sternal gland structures in males of bean flower thrips, Megalurothrips sjostedti, and Poinsettia thrips, Echinothrips americanus, in comparison with those of western flower thrips, Frankliniella occidentalis (Thysanoptera: Thripidae).

Sternal pores are important features for identification of male thrips, especially within the subfamily Thripinae. They vary in shape, size and distribution even between species of one genus. Their functional role is speculated to be that of sex- and/or aggregation pheromone production. Yet, sexual aggregations are not reported in Echinothrips americanus, known to have sternal pores, while we observed aggregations in Megalurothrips sjostedti, previously reported to lack them. We examined the sternal glands and pores of the thripine species E. americanus and M. sjostedti males, in comparison with those of Frankliniella occidentalis using light microscopy, as well as scanning and transmission electron microscopy. Pore plates of F. occidentalis were ellipsoid and medial on sternites III-VII, while in E. americanus they were distributed as multiple micro pore plates on sternites III-VIII. In M. sjostedti they appeared as an extremely small pore in front of the posterior margin of each of sternites IV-VII. Pore plate and pore plate area were distributed similarly on sternites III-VII in F. occidentalis. However, in E. americanus the total pore plate area increased significantly from sternites III to VIII. Ultrastructure of cells associated with sternal glands showed typical characteristics of gland cells that differ in size, shape and number. The function of sternal glands is further discussed on the basis of morphological comparisons with other thrips species.

Alkaloid metabolism in thrips-Papaveraceae interaction: recognition and mutual response.

Frankliniella occidentalis (Pergande), the Western Flower Thrips (WFT), is a polyphagous and highly adaptable insect of the order Thysanoptera. It has a broad host range but is rarely found on Papaveraceae, which might be due to deterrent effects of alkaloids present in most species of this family. In order to test the adaptive potential of WFT, we investigated its interaction with two Papaveraceae offered as sole feeding source. We found that WFT are able to live and feed on leaves of Eschscholzia californica and Chelidonium majus. Both plants respond to thrips feeding by the enhanced production of benzophenanthridine alkaloids. Furthermore, cell cultures of E. californica react to water insoluble compounds prepared from adult thrips with enhanced alkaloid production. During feeding, WFT take up benzophenanthridine alkaloids from either plant and from an artificial feeding medium and convert them to their less toxic dihydroderivatives. This was shown in detail with sanguinarine, the most cytotoxic benzophenanthridine. A similar conversion is used in plants to prevent self-intoxication by their own toxins. We conclude that WFT causes a phytoalexin-like response in Papaveraceae, but is able to adapt to such host plants by detoxification of toxic alkaloids.