Morphology of the Female Reproductive System of the Soybean Thrips, Neohydatothrips variabilis (Beach, 1896) (Thysanoptera: Thripidae)

SIMPLE SUMMARY: Soybean thrips are an important vector of Soybean vein necrosis virus disease, found in all soybean-growing regions of the United States and Canada. The disease reduces the seed oil content and fatty acid profiles in infected plants. It is important to know the morphology of the female reproductive system of soybean thrips to understand the egg-laying mechanism and develop strategies for virus vector management. For this purpose, we used fuchsin staining, paraffin-based histology, dissections, serial block-face scanning electron microscopy and confocal laser scanning microscopy techniques to understand the structure and motorization of the internal and external genitalia of soybean thrips. We also investigated the egg-laying behavior of soybean thrips. The female reproductive system is composed of two ovaries, an oviduct, an accessory gland, an appendage gland, a common oviduct and a vagina. Female soybean thrips lay eggs in the parenchymatous tissues near the veins of the leaves. The appendage gland likely secretes lubrication to facilitate the movement of eggs through the external genitalia. Seven muscles support the movement of eggs from the ovaries to the leaf surface. The anatomy and probable role of each muscle is also described. ABSTRACT: Soybean thrips (Neohydatothrips variabilis) are an important phytophagous vector of the widely recognized Soybean vein necrosis orthotospovirus (SVNV). Understanding the egg-laying behavior of these thrips could aid in developing strategies for the management of the vector and virus. In this study, we described the egg-laying behavior of N. variabilis and reconstructed the three-dimensional morphology of the female terminalia by using serial block-face scanning electron microscopy (SBFSEM) and confocal laser scanning microscopy (CLSM). The female reproductive system consists of two panoistic ovaries consisting of eight ovarioles. The appendage gland is connected to the ovaries by two muscles, and to the body wall by a single muscle. The spermatheca is connected to the eighth tergum through four branched muscles, to the basivalvulae of the ovipositor by one muscle and to the vagina by a single muscle. The external genitalia are operated by seven muscles. The movement of the eggs inside the ovipositor is achieved by the back and forth “rocking” movement of the first valvulae and valvifer. Eggs are deposited into the parenchymatous tissue alongside leaf veins. To the best of our knowledge, this is the first study describing the internal and external genitalia of N. variabilis.