We all are aware that all animals and plants have their own defence systems that they use against predators. Insects are also included in this category. Burnet moths have not only adapted to their host's cyanogenic glucosides but also have the ability to synthesize and sequester hydrogen cyanide. Let us find out how...
Most of the times, these compounds are toxic, but herbivores and pathogens of such plants develop a tolerance to these chemicals. This process is known as co-evolution and can lead to organisms turning dependent on the plant's compounds for their own development. Many insects are resistant to cyanide-producing plants. Some burnet moths that belong to the family Zygaenidae have even evolved an ability to synthesize the same cyanogenic compounds as their host plants. They have specialized uses for the cyanide such as using it during their mating process.
Some toxic compounds that are present constitutively are known as phytoanticipins. Cyanogenic glucosides (Cnglcs) are one class of these compounds. These are inactive compounds that have hydrogen cyanide (HCN) bound to a sugar molecule. They release HCN and when the tissue is damaged, and the compounds interact with a specialized beta glucosidase enzyme. The Cnglc and the beta glucosidase are stored in separate compartments and only meet when the tissue is disrupted, such as by an insect's chewing.
Insects that feed on a broad array of plants are likely to be deterred by the presence of HCN in a plant. Those that depend on a particular species of plant make cyanide frequently adapted to not only tolerate the HCN, but also to sequester it from the plant. By doing so, these specialized insects can utilize Cnglcs to defend themselves against predators.
Various species of insects utilize Cnglcs that they have sequestered from plants. Several types of insects can synthesize HCN including some species in the orders of beetles, true bugs, and moths and butterflies. Their predators are not adapted to the effect of cyanide, which inhibits the mitochondrial oxidation step of cellular respiration.
Burnet Moths Produce Cyanogenic Glucosides
Burnet moths are capable of synthesizing HCN. The most well studied system is that of Zygaena filipendulae, the six-spotted burnet moth. This insect makes the same cyanogenic compounds as its host-limanarin and lotaustralin and the most common type of Cnglcs in plants and insects. The larvae also prefer to feed on plants with high amounts of cyanide compared to those that produce little or no HCN.
Cyanogenic Glucosides used during mating
These Zygaena moths are highly specialized in their use of limanarin and lotaustralin. Besides from being used to defend themselves against predators, these Cnglcs are used in various aspects of mating of the six-spotted burnet moth. The females release a plume of hydrogen cyanide when they are perched and while they are waiting for a male. It is thought that this cyanide is acting as a pheromone or a chemical attractant for the male.
Females prefer to mate with males that have greater concentrations of cyanide. The males give the Cnglcs to the females as a "nuptial gift" during mating. They transfer the cyanogenic compounds to the females. This extra HCN helps the females better protect her eggs. The Cnglcs are also used as a source of stored reduced nitrogen and sugar for the insects.
Definitely, it is amazing to know how these cyanogenic compounds are produced.