Which of the following statement (s) is/are correct with regard to biocontrol agents?

All of the above statements are correct.

The correct answer is Option (4)- All of the above statements are correct.

(a) Ladybird beetles and dragonflies are used to get rid of aphids and mosquitoes, respectively: This statement is correct. Ladybird beetles, also known as ladybugs or ladybirds, are beneficial insects that feed on aphids, which are pests that can damage plants. Ladybird beetles are often introduced into agricultural fields or gardens as a form of biological control to naturally reduce aphid populations. Similarly, dragonflies are natural predators of mosquitoes and their larvae. Dragonflies are known for their voracious appetite for mosquitoes and are commonly used as a biocontrol agent to control mosquito populations in certain areas.

(b) Bacillus thuringiensis bacteria are used to control butterflies and caterpillars: This statement is also correct. Bacillus thuringiensis (Bt) is a bacterium that produces crystal proteins toxic to certain insects, including butterflies and caterpillars. These proteins, known as Bt toxins, are selectively toxic to specific groups of insects and are harmless to other organisms. Bt-based biopesticides, derived from Bt bacteria or their toxin genes, are used as an effective and environmentally friendly method to control butterfly and caterpillar pests in agriculture and horticulture.

(c) Trichoderma species are used to control several plant pathogens: This statement is correct as well. Trichoderma species are filamentous fungi that have been widely used as biocontrol agents against various plant pathogens. Trichoderma species have the ability to colonize plant roots and inhibit the growth of pathogenic fungi through mechanisms such as competition for resources, production of antifungal compounds, and stimulation of plant defense responses. They are used in agricultural practices and integrated pest management strategies to suppress diseases caused by fungal pathogens.

(d) All of the above statements are correct: Based on the explanations provided, it can be concluded that all of the above statements are correct. Ladybird beetles and dragonflies are used as biocontrol agents for aphids and mosquitoes, respectively. Bacillus thuringiensis is used for the control of butterflies and caterpillars, and Trichoderma species are utilized to control various plant pathogens. These biocontrol agents offer environmentally friendly alternatives to chemical pesticides, promoting sustainable and eco-friendly pest management practices.