Beetle
Mating

Some beetles have intricate mating behaviour. Pheromone communication is often important in locating a mate.Different species use different pheromones. Scarab beetles such as the Rutelinae use pheromones derived from fatty acid synthesis and others use pheromones from organic compounds, while other scarabs such as the Melolonthinae use amino acids and terpenoids. Another way beetles find mates is seen in the fireflies (Lampyridae) which are bioluminescent, with abdominal light-producing organs. The males and females engage in a complex dialog before mating; each species has a unique combination of flight patterns, duration, composition, and intensity of the light produced.

Before mating, males and females may stridulate, or vibrate the objects they are on. In the Meloidae, the male climbs onto the dorsum of the female and strokes his antennae on her head, palps, and antennae. In Eupompha, the male draws his antennae along his longitudinal vertex. They may not mate at all if they do not perform the precopulatory ritual. This mating behavior may be different amongst dispersed populations of the same species. For example, the mating of a Russian population of tansy beetle (Chrysolina graminis) is preceded by an elaborate ritual involving the male tapping the female's eyes, pronotum and antennae with its antennae, which is not evident in the population of this species in the United Kingdom.

In another example, the intromittent organ of male thistle tortoise beetles is a long, tube-like structure called the flagellum which is thin and curved. When not in use, the flagellum is stored inside the abdomen of the male and can extend out to be longer than the male when needed. During mating, this organ bends to the complex shape of the female reproductive organ, which includes a coiled duct that the male must penetrate with the organ. Furthermore, these physical properties of the thistle tortioise beetle have been studied because the ability of a thin, flexible structure to harden without buckling or rupturing is mechanically challenging and may have important implications for the development of microscopic catheters in modern medicine.

Competition can play a part in the mating rituals of species such as burying beetles (Nicrophorus), the insects fighting to determine which can mate. Many male beetles are territorial and fiercely defend their territories from intruding males. In such species, the male often has horns on the head or thorax, making its body length greater than that of a female. Copulation is generally quick, but in some cases lasts for several hours. During copulation, sperm cells are transferred to the female to fertilize the egg.
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