Imidacloprid-mediated alterations on the salivary glands of the Neotropical brown stink bug, Euschistus heros.

The management of the Neotropical brown stinkbug Euschistus heros (Hemiptera: Pentatomidae) in soybean fields has been heavily dependent on the application of neonicotinoid insecticides. Neonicotinoids act primarily by impairing the function of the nicotinic acetylcholine receptors of the nervous system. These compounds also target specific organs (e.g., salivary glands), which may potentiate their insecticidal efficacy. Here, we evaluated whether the exposure to the neonicotinoid imidacloprid would cause cytomorphological changes in the salivary glands of E. heros. First, we determined the lethal concentrations (LCs) of imidacloprid through contact and ingestion. Subsequently, the cytomorphology of the salivary glands were evaluated in insect groups that survived exposure to the LC5 (3.75 mg a.i./L), LC50 (112.5 mg a.i./L), or LC75 (375.0 mg a.i./L, equivalent to the recommended field rate) doses. Imidacloprid induced apoptosis and necrosis in the salivary gland cells according to the insecticide concentration and salivary gland region. All concentrations increased apoptosis and injured cells (e.g., vacuolization, chromatin condensation, swelling of organelles, and plasma membrane rupture) in the principal and accessory salivary glands. Individuals that survived exposure to the highest concentrations (i.e., LC5 and LC50) were more affected, and exhibited several necrotic cells on their main principal salivary glands. Collectively, our results indicate that imidacloprid exerts toxic effects on the non-target organs, such as the salivary glands, which increases the efficacy of this compound in the management of stink bug infestations.

Anatomy, Histology, and Ultrastructure of Salivary Glands of the Burrower Bug, Scaptocoris castanea (Hemiptera: Cydnidae).

The burrower bug Scaptocoris castanea Perty, 1830 (Hemiptera: Cydnidae) is an agricultural pest feeding on roots of several crops. The histology and ultrastructure of the salivary glands of S. castanea were described. The salivary system has a pair of principal salivary glands and a pair of accessory salivary glands. The principal salivary gland is bilobed with anterior and posterior lobes joined by a hilus where an excretory duct occurs. The accessory salivary gland is tubular with a narrow lumen that opens into the hilus near the excretory duct, suggesting that its secretion is stored in the lumen of the principal gland. The cytoplasm of the secretory cells is rich in the rough endoplasmic reticulum, secretory vesicles with different electron densities and mitochondria. At the base of the accessory gland epithelium, there were scattered cells that do not reach the gland lumen, with the cytoplasm rich in the rough endoplasmic reticulum, indicating a role in protein production. Data show that principal and accessory salivary glands of S. castanea produce proteinaceous saliva. This is the first morphological description of the S. castanea salivary system that is similar to other Hemiptera Pentatomomorpha, but with occurrence of basal cells in the accessory salivary gland.

Ultrastructure of the Salivary Glands of the Stink Bug Predator Podisus distinctus.

Podisus distinctus (Hemiptera: Pentatomidae) is a zoophytophagous insect with significant potential for use as a biological control agent in agriculture and forestry because their nymphs and adults actively prey on diverse insect species. The saliva of this insect possesses active substances that cause paralysis and death of the prey. As the first step in identifying compounds of P. distinctus saliva, this study describes the ultrastructure of the salivary glands of this predator. The salivary system of P. distinctus possesses a pair of main salivary glands with a short anterior lobe, a long posterior lobe, and a pair of tubular accessory glands. The main salivary gland of P. distinctus has no associated muscles, suggesting that the saliva-release mechanism occurs with the help of certain thorax muscles. The main salivary gland epithelium has a single layer of cells (varying from cubical to columnar) with cytoplasm rich in rough endoplasmic reticulum, spherical granules of different sizes, a nucleus with a predominance of decondensed chromatin, and nucleolus. The apical cell region has a few short microvilli and the basal region has plasma membrane infoldings. The epithelium of the accessory salivary glands possesses a single-layered epithelium of cubic cells delimiting a narrow lumen. The apical cell region has a high density of microvilli and pleomorphic mitochondria, whereas the central cell region is rich in rough endoplasmic reticulum with a well-developed nucleus and decondensed chromatin. The basal cell region is characterized by the presence of several basal plasma membrane infoldings associated with mitochondria and numerous openings to the hemocoel forming large channels. The ultrastructural characteristics suggest that the main salivary glands and accessory salivary glands play a vital role in protein synthesis for saliva production and that the accessory glands are involved in transport of materials of the hemolymph.

Comportamento de predação de podisus nigrispinus (dallas, 1851) (hemiptera: pentatomidae) em função da disponibilidade de alimento

ABSTRACT Predators with extraoral digestion may consider several factors to attack a prey item based not only on the nutritional value but also on the energy expended in prey handling (capture, digestion and ingestion of liquefied content). The predatory stinkbug may require a large amount of water to produce saliva and enzymes used to digest prey tissues and, hence, exhibit behavior related to the water source. Thus, this study investigated the behavioral choice of the predator between a moisture source (water and plant) and a prey item and weight gain by the predatory stinkbug Podisus nigrispinus (Dallas) (Hemiptera: Pentatomidae). Predator adults had free choice to feed between water and the pre-pupa of Alabama argillacea (Hübner, 1823) (Lepidoptera: Noctuidae) (i), between the host plant (cotton) and larvae of A. argillacea (ii), or on each of these food sources individually (iii). Although starved for 48h, P. nigrispinus exhibited a similar choice between feeding either on water or on prey, and preferred to feed on plants compared to prey when having access to prey and cotton plants simultaneously. Under the non-choice test, predators chose to feed on the prey, and showed a similar choice to feed or not on the water and plant. Thus, the predator P. nigrispinus exhibited feeding behavior driven by the availability of the moisture source. Despite the greater time of feeding on prey, predators gained weight in all food items indicating significant ingestion of food material. Therefore, these results characterize the role of the moisture source on P. nigrispinus predatory behavior, indicating it as one factor that should be considered when studying predation rate with this and other predators with extra-oral digestion.

RESUMO Predadores com digestão extra-oral devem considerar vários fatores para atacar uma presa baseado na sua necessidade nutricional e no investimento para a sua manipulação. Este estudo investigou o comportamento de escolha entre uma fonte de umidade e uma presa pelo percevejo predador Podisus nigrispinus (Dallas) (Hemiptera: Pentatomidae) e ganho de peso dependendo de sua escolha. Predadores adultos, após 48h sem alimentação, foram submetidos a três tipos de escolha: (i) água e pré-pupa de Alabama argillacea (Hübner, 1823) (Lepidoptera: Noctuidae), (ii) planta hospedeira (algodoeiro) e lagartas de A. argillacea (iii) e cada fonte de alimento individualmente. P. nigrispinus exibiu escolha similar entre alimentar-se da presa ou de água e mostrou preferência por plantas em comparação à presa. Quando sem chance de escolha, os predadores preferiram atacar a presa e exibiram similar escolha em alimentar-se ou não de água ou planta. Observou-se que o comportamento de predação de P. nigrispinus foi influenciado pela disponibilidade de uma fonte de umidade. Os predadores, apesar de possuir maior tempo de alimentação sobre a presa, apresentaram ganho de peso em todas as fontes de alimento com ingestão significante de água e seiva de planta. Tais resultados caracterizam a importância da presença da água no comportamento de predação de P. nigrispinus e que a sua disponibilidade deve ser considerada em estudos de comportamento de predação com este e/ou outros predadores com digestão extra-oral.