Abstract
The aim of this study was to determine the effect of the insecticide pyriproxyfen (Tiger™ 100 CE), juvenile hormone analogue, when applied in a sublethal LC30 concentration (0.668 mL a. i. L-1), on the morphological and morphometric parameters of external and internal connective tissue (CT) of the Neotropical-brown stink bug Euschistus heros testicles. The insecticide was applied on nymphs from the 4th instar using a Potter tower with a working pressure of 82.73 kPa (12 lb pol-²) and 1 mL of the emulsion per replicate. A completely randomized experimental design was used, consisting of two treatments (control and pyriproxyfen-treated), five repetitions, and 10 adults of E. heros per experimental unit. The insects were maintained under controlled conditions until the emergence of adults. After 48 h of emergence of adults, the testicles were collected, fixed, and processed for morphological and morphometric analyses. A change was observed in the collagen fibers of the CT of treated insects when compared with those of controls. It was also observed that both types of CT (dense irregular and loose) over the internal tunic of the treated insect were thinner than those in control insects. The analysis showed that pyriproxyfen significantly reduced the external and internal CT width and the conformation of its fibers in all the observed regions when compared with the controls; this may affect the production of the three different types of sperm present in this species.
Highlights
The Neotropical Brown stink bug Euschistus heros (Fabricius, 1798) (Hemiptera: Pentatomidae) is considered an important insect within the pest complex that causes expensive damage in soybean crops in Brazil (Soares, Cordeiro, Santos, Omoto, & Correa, 2018).The application of chemical insecticides remains the main control strategy against stink bugs (Corrêa-Ferreira & Sosa-Goméz, 2017)
Pyriproxyfen stands out as a potential alternative to neurotoxic insecticides due to its selectivity based on its mode-of-action as an analogue to the juvenile hormone (JH), which “per se” is naturally produced and secreted by the insect’s neuroendocrine system (Nauen, Slater, Sparks, Elbert, & Mccaffery, 2019)
The external connective tissue (CT) was formed in the external CT sheath by strongly eosin-stained, dense, thick fibers, placed in a random arrangement which is very characteristic of collagen fibers (Figure 2A)
Summary
The Neotropical Brown stink bug Euschistus heros (Fabricius, 1798) (Hemiptera: Pentatomidae) is considered an important insect within the pest complex that causes expensive damage in soybean crops in Brazil (Soares, Cordeiro, Santos, Omoto, & Correa, 2018).The application of chemical insecticides remains the main control strategy against stink bugs (Corrêa-Ferreira & Sosa-Goméz, 2017). Regarding the exposure to xenobiotic agents and insecticides, pest insects may develop physiological adaptive aspects at multiple levels (Samantsidis et al, 2020), and this characteristic often has direct effects on the development of the reproductive system, as observed in some pest stink bugs (Aguiar et al, 2017; Cremonez, Pinheiro, Falleiros, & Neves, 2017). This occurs either by means of resource reallocation in the development of the insect or by the direct action of the insecticide, depending on its mode of action.
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