Black chafer beetles come out to mate on a 48-hour schedule

A new study published in the journal Current Biology unveils the unusual biological rhythm of the large black chafer beetle, Holotrichia parallela, an agricultural pest in Asia. Contrary to the typical 24-hour cycle that governs most life on Earth, these beetles operate on a rare 48-hour cycle, termed “circa-bi-dian.” 

Intriguing mating behavior 

The research, led by Walter Leal, professor of molecular and cellular biology at the University of California, Davis, and Jiao Yin at the Chinese Academy of Agricultural Sciences in Beijing, examines the beetle’s mating behavior which occurs every other night.

Female beetles of this species emerge from the soil bi-nightly, climbing host plants to release pheromones and attract males. The research team, intrigued by this behavior, investigated whether the male beetles’ ability to detect these pheromones was also controlled by a 48-hour clock.

Chemical sensing

The study’s focus on the beetle’s chemical sensing, particularly how insects use scent to attract mates, led to identifying the gene responsible for reacting to the female pheromone, L-isoleucine methyl ester (LIME). After cloning 14 candidate genes, the team identified HparOR14 as the sex pheromone receptor. 

The researchers found that on the nights when females would be releasing scents, there was an increase in the transcription of HparOR14 after dark, while on alternate days, the receptor activity was low.

48-hour circabidian cycle

This research confirms that the male chafer beetle’s ability to detect female pheromones operates on a 48-hour circabidian cycle, aligning with the females’ mating behavior. However, the study raises questions about the reasons behind these beetles’ unique 48-hour cycles. 

Since there are no environmental cues on a 48-hour scale, it remains a mystery how these circabidian cycles are set and synchronized.

Rare observations 

“Twenty-four hour rhythms in physiology and behavior are commonly observed in organisms from bacteria to humans, but observations of 48-hour rhythms in nature are rare,” said Professor Joanna Chiu, chair of the Department of Entomology and Nematology at UC Davis and an expert on circadian rhythms, who was not involved in the research. 

“This elegant study by Professor Leal and his collaborators has provided us with an in-depth description of how the circabidian rhythm of pheromone detection in this beetle is generated.”

This study not only provides a new understanding of the complex mechanisms of biological timekeeping but also opens new avenues for research into how such unique rhythms evolved and their ecological significance.

Black chafer beetles

Black chafer beetles belong to a group of beetles known for their dark, often black coloration and their robust, rounded bodies. They are part of the family Scarabaeidae, which includes many familiar beetles like dung beetles, June beetles, and the famous scarabs of ancient Egyptian iconography. These beetles are found in various environments across the world.

Appearance 

Adult black chafer beetles are typically characterized by their shiny black exoskeletons. They vary in size, but many are medium-sized beetles. The larvae of these beetles are often referred to as grubs and are commonly found in soil. They are C-shaped, whitish in color, with a distinct head and often feed on decomposing plant material or roots. This feeding habit can make them agricultural pests, as they can damage crops and lawns.

Life cycle

The life cycle of the black chafer beetle includes several stages: egg, larva, pupa, and adult. The females lay eggs in the soil, which hatch into larvae. These larvae undergo several molts, growing larger each time. After reaching a certain size, they pupate in the soil, eventually emerging as adults. The complete cycle can vary in length depending on the species and environmental conditions.

Behavior 

In terms of behavior, adult black chafer beetles are often seen flying to lights at night. They are typically most active during the warmer months of the year. Some species are known to feed on plant foliage, which can cause damage to gardens and crops.

Management 

In controlling black chafer beetles, especially in agricultural or horticultural contexts, various methods are employed. These can include cultural practices like crop rotation and the use of pesticides. Biological control measures, like introducing natural predators or parasitic organisms, are also explored as sustainable and eco-friendly options.

Image Credit: Holotrichia parallela observed in Hong Kong by ltong__, licensed under http://creativecommons.org/licenses/by-nc/4.0/. 

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