Hemiptera's Resilience: Tolerating Pollution

Hemiptera, or true bugs, are an order of insects that feed on plant sap and other insects. They are known to be pests to humans, damaging crops and transmitting diseases. With over 95,000 named species, they are the largest order of hemimetabolous insects. Some Hemiptera are aquatic or semi-aquatic, and play a significant role in organic material turnover and energy flow. Despite their abundance in almost all water types, they are often ignored in water pollution biomonitoring schemes. This raises the question: are Hemiptera tolerant to pollution?

The impact of pesticides on Hemiptera

Hemiptera, or "true bugs", are insects that feed on plants, blood, or other insects. They are known to be pests to crops and transmit diseases to humans. Humans have interacted with Hemiptera for millennia and have used pesticides to control their populations.

Transgenic crops expressing toxins derived from the bacterium Bacillus thuringiensis (Bt) have been effective in protecting plants against some insect pests. However, these toxins have shown little toxicity against sap-sucking insects like Hemiptera. In some cases, the pest status of Hemiptera has increased on Bt-transgenic plants when pesticides are not applied.

The development of resistance to chemical insecticides and the limited effectiveness of Bt toxins highlight the need for alternative management strategies. One approach is to focus on transgenic resistance to Hemiptera pests. By understanding the biology and feeding mechanisms of Hemiptera, scientists can develop strategies to disrupt their feeding or reproductive processes.

Additionally, some species of Hemiptera have been found to play a role in biomonitoring water pollution. While they are often labeled as moderately sensitive or tolerant to water pollution, they can provide valuable data on the ecotoxicological effects of pollutants such as heavy metals and pesticides. This information can be used to assess water quality and the impact of pollution on aquatic ecosystems.

Hemiptera's role in organic material turnover

Hemiptera is an order of insects, commonly called "true bugs", comprising more than 80,000 species within groups such as the cicadas, aphids, planthoppers, leafhoppers, assassin bugs, bed bugs, and shield bugs. They are distinguished by their piercing-sucking mouthparts, which may consist of an elongated beak or short cone jutting out from the front of the head. This unique beak-like structure allows them to feed on plant sap, making them sap-sucking insects.

Hemipterans play a significant role in organic material turnover, especially in agricultural contexts. Most hemipterans are phytophagous, feeding on the sap of plants. They use their specialized mouthparts to pierce and suck out the plant's sap, which can cause direct damage to crops. This feeding behaviour results in a loss of nutrients and moisture for the plants, impacting their growth and health.

Additionally, hemipterans can act as vectors for the transmission of plant viruses, causing indirect damage to crops. Their ability to transmit pathogens, including viruses, bacteria, and phytoplasmas, further contributes to their role in organic material turnover. Some hemipterans, such as aphids, are capable of rapid reproduction through parthenogenesis, which exacerbates their impact on agricultural ecosystems.

However, it's important to note that not all hemipterans are pests. Some hemipterans, like assassin bugs, are predators that feed on other insects or small invertebrates. They play a regulatory role in ecosystems by controlling the populations of their prey. Additionally, certain species of hemipterans have been utilized by humans for biological control of insect pests or invasive plants.

The impact of hemipterans on organic material turnover is significant, and their interactions with plants and other organisms in the ecosystem are complex. While they can cause damage as agricultural pests, they also contribute to the natural dynamics and balance of ecosystems.

The effect of heavy metals on Hemiptera

Hemiptera is the largest order of hemimetabolous insects, containing more than 95,000 named species. They live in a wide variety of habitats, generally terrestrial, though some are adapted to life in or on the surface of freshwater. The defining feature of hemipterans is their "beak", which they use to pierce tissues and suck liquids.

Some hemipterans live in close contact with contaminated sediments and are thus more exposed to heavy metals. Heavy metals can be transferred to hemipterans through food chains and cause various chronic toxicological effects on their growth and physiology. For example, zinc and manganese were negatively associated with the diversity and richness of the hemipteran community in the Kerian River Basin, Malaysia.

In another study, cadmium exposure was found to impact the insecticidal cross-resistance and biological traits of the Brown planthopper Nilaparvata lugens (Hemiptera: Delphacidae). The findings suggest that insect bioindicators can be used to identify and track environmental contamination.

The combined effect of an entomopathogenic agent and heavy metal stress can also cause much higher overall insect mortality than either stressor alone. This area of research has great potential for optimizing biocontrol strategies against agricultural or forest pests in heavy metal-polluted areas.

In conclusion, heavy metals can have significant effects on Hemiptera, impacting their growth, physiology, and mortality. The presence of heavy metals in the environment can also influence the diversity and richness of hemipteran communities. Further research is needed to fully understand the effects of heavy metal exposure on Hemiptera and to develop effective strategies for mitigating these impacts.

Hemiptera's tolerance to different salinities

Hemiptera is the largest order of hemimetabolous insects, containing more than 95,000 named species. The majority of species are terrestrial, but some are found in freshwater habitats, including water boatmen, backswimmers, pond skaters, and giant water bugs.

Some Hemiptera are highly tolerant of pollution, with a score of 7.5 out of 10 for the "Southeast" region, according to one source. However, it is unclear what specific pollutants are being referred to in this context.

Regarding their tolerance to different salinities, one study focused on Trichocorixa verticalis (an aquatic hemipteran native to North America) and its invasion of the Iberian Peninsula. This species was found to have a higher range of mean responses across various treatments, including high temperatures and conductivity. T. verticalis was also the most resistant to high conductivity at the egg stage, while another species, Sigara selecta, showed the highest halotolerance as adults. The study suggests that the ability of T. verticalis to perform well at higher salinities and temperatures may contribute to its successful invasion of Mediterranean areas.

Another study investigated the effects of reduced salinities on the thermal tolerance of hypersaline specialist diving beetles, including Sigara lateralis (a native species) and Trichocorixa verticalis verticalis (an invasive species in South-West Spain). The results indicated that only T. v. verticalis showed a decrease in SCP (supercooling point) after exposure to both high temperature and conductivity. This suggests that while S. lateralis may have a broader thermal range, T. v. verticalis exhibits greater plasticity and adaptability to different environmental conditions.

In summary, while Hemiptera as a whole may exhibit varying levels of tolerance to different salinities, the available literature specifically mentions the tolerance of Trichocorixa verticalis and its impact on its invasive nature in certain regions. The ability to tolerate a range of salinities, along with other factors like temperature and conductivity, can contribute to the success and spread of certain Hemiptera species in new environments.

The evolution of Hemiptera's feeding mechanisms

Hemiptera is the largest order of hemimetabolous insects (insects that do not undergo complete metamorphosis), containing more than 95,000 named species. The defining feature of hemipterans is their "beak", formed by modified mandibles and maxillae, which create a stylet sheathed within a modified labium. The stylet is capable of piercing tissues and sucking liquids, while the labium supports it. The stylet contains two channels: one for the outward movement of saliva and another for the inward movement of liquid food.

The diet of hemipterans is typically plant sap, which they extract using their sucking and piercing mouthparts. This relationship between hemipterans and plants appears to be ancient, with piercing and sucking of plants evident in the Early Devonian period. Some hemipterans are monophages, meaning they are host-specific and only feed on one plant taxon. Others are oligophages, feeding on a few plant groups, while some are polyphages, feeding on many species of plants.

Some hemipterans, such as assassin bugs, are predators. Both herbivorous and predatory hemipterans inject enzymes to begin digestion extra-orally (before the food is taken into the body). Most aquatic true bugs are piercer-predators, seizing their prey with their front legs before using their specialised mouthparts to pierce and suck out their meal.

Some hemipterans are bloodsucking, or hematophagous, feeding on other insects or small invertebrates. Examples include the bed bug, a persistent parasite of humans, and kissing bugs, which can transmit Chagas disease.

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