The insects as an assessment tool of ecotoxicology associated with metal toxic plants

The Investigation of the Impact of Toxicity of Metals on Oxygen-Evolving Complex in Spinacia oleracea

The current article reported the investigation of metal toxicity on the oxygen-evolving complex (OEC) in Spinacia oleracea related to depletion in chloride ion concentration, an essential part of the photosystem (II). The greenhouse experiment was conducted where S. oleracea was cultivated in three replicates with control plants (plants “a”) treated with tap water. Moreover, 30 ppm of Cu²⁺ ion solution and Pb²⁺ ion solution was used to irrigate the rest of the plants, labeled as plants “b” and “c”, respectively, on alternative days. Advanced technologies such as Atomic Absorption Spectrophotometry (AAS), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), and UV-visible Spectrophotometry were used to monitor the essential nutrients in leaves to validate the function of the photosystem (I and II). Reduced Cl⁻ ions contents showed that both metals (Cu²⁺ and Pb²⁺) altered the essential elements of the oxygen-evolving complex (OEC) of photosystem (II), required to maintain the coordination structure of the Mn₄CaO₅ cluster. SEM analysis revealed the modified leaf structure of the S. oleracea under Cu²⁺ and Pb²⁺ accumulation due to which distorted cellular structure, reduced surface area, and the (shattered) stomatal opening compared to the plants “a” were observed. The EDS analysis of plants “b” and “c” showed high oxygen contents followed by reduced chloride contents over plants “a”, reflecting the infirmity of OEC to push out oxygen, which leads to generating oxidative stress. The lower pigment concentration in leaves of metal-contaminated plants “b” and “c” impacts carbon assimilation, which is linked to the reduced stomatal opening and influences the gaseous exchange rates. Additionally, increased contents of K⁺ and Ca²⁺ may be due to self-defense mechanisms under low chloride contents to speed up oxygen evolution to protect plants against oxidative stress. It was concluded that Cu²⁺ and Pb²⁺ metal toxicity influences essential Cl⁻ and K⁺ contents, which modify the photosystem II system; subsequently, a reduced growth rate was observed.

Laboratory induced selection of pyriproxyfen resistance in Oxycarenus hyalinipennis Costa (Hemiptera: Lygaeidae): Cross-resistance potential, realized heritability, and fitness costs determination using age-stage, two-sex life table

Pyriproxyfen is a biorational insecticide from IGR family, used worldwide against several economic pests. To evaluate the risk of pyriproxyfen resistance in dusky cotton bug, Oxycarenus hyalinipennis Costa (Hemiptera: Lygaeidae), a major concern for cotton producers, and to formulate strategies effective to tackle resistance, a field collected population was selected with pyriproxyfen under laboratory conditions using seed-dip method. A resistant strain designated as Pyr-SEL (G₁₈) was developed after repeatedly selecting O. hyalinipennis with pyriproxyfen over eighteen generations. Thereafter, fitness costs, realized heritability (h²) and cross-resistance were investigated. As a result of selection, Pyr-SEL (G₁₈) developed a very high level of resistance (resistance ratio = 464.23-fold) compared with the susceptible strain unselected over twenty generations Un-SEL (G₂₀). The Pyr-SEL (G₁₈) conferred strong cross-resistance to bifenthrin (146.59-fold), lambda-cyhalothrin (132.96-fold) and fenoxycarb (91.06-fold), whereas showed moderate cross-resistance to diafenthiuron (28.86-fold) and fipronil (22.73-fold). The h² estimate was 0.16 in Pyr-SEL (G₁₈). The developmental duration of O. hyalinipennis pre-adult prolonged, but traits of λ, r and R₀ reduced in Pyr-SEL (G₁₈) compared with the Un-SEL (G₂₀). Also, the population projection obtained lower population size for Pyr-SEL (G₁₈) than Un-SEL (G₂₀). Fitness studies revealed that high resistance development to pyriproxyfen lowered the relative fitness of Pyr-SEL (G₁₈) (R_f = 0.38) compared with the Un-SEL (G₂₀). These findings may be practically valuable in tackling O. hyalinipennis resistance for better pest management.

Revisiting the concept of entomotoxicology

Until now, the term entomotoxicology has only been used in medico-legal sciences. However, entomotoxicology as a whole has a much wider scope and forensic entomotoxicology is just one of its branches. Based on the literature a wider definition of the term is presented. Today, we can distinguish two major branches of entomotoxicology: 1) Forensic entomotoxicology, which uses the insects as evidence of the presence of xenobiotics in decomposing tissue during an investigation and 2) Environmental entomotoxicology, which uses the insects as bioindicators of environmental pollution in non-criminal circumstances. While forensic entomotoxicology is a relatively new discipline, research in environmental entomotoxicology began as far back as the 1920s. A review of the work in entomotoxicology from the last 6 years is presented, covering several interesting new trends. This article aims to redefine entomotoxicology, which should increase awareness to bring more collaborations and multidisciplinary between related scientific fields.