A genetic blueprint of the bedbug could expose chinks in the armour of the unsocial insect which is becoming an increasing menace around the world, say scientists.

The completed genome sequence of Cimex lectularius has revealed some of the multiple ways bedbugs have evolved to resist insecticides.

Their armour-like outer cuticle has barriers and detoxification genes that keep out the chemicals, the research shows.

In addition, many bedbugs have made it harder for insecticides to target their nervous systems through sodium channel "gates".

The bugs may also render ingested pesticides harmless using the same system they use to detoxify blood, the study suggests.

DNA analysis indicates high levels of interbreeding among the bugs, which would make it easier for genetic resistance to pesticides to spread across populations.

Bedbugs have plagued humans for at least 3,000 years, but widespread use of insecticides in homes curbed their numbers dramatically after the Second World War.

In the last two decades, the bedbug has staged a spectacular comeback, rising from near-eradication levels in many regions to become established in every continent except Antarctica. In Australia alone, bedbug infestation rates have risen 4,500%.

Dr Michael Scharf, from Purdue University in the US, said: "Nobody was ready for this. It's reached almost a crisis condition. All big cities in the US are experiencing problems.

"Our culture had forgotten about bedbugs, and two generations of entomologists haven't had to deal with them."

Co-author Dr Zach Adelman, from Virginia Polytechnic Institute and State University in the US, said: "Understanding how the bedbug genome is adapting to resist control methods is crucial for stopping the resurgence of the pest."

The new research is reported in the journal Nature Communications.

Adult bedbugs have flat, reddish-brown bodies up to a quarter of an inch long and piercing blood-sucking mouth parts that can penetrate human skin.

Although they do not transmit disease, their bites can result in secondary infections and cause psychological distress.