Dinosaurs became extinct from the effects of a massive asteroid hitting Earth 65 million years ago, scientists have long maintained. But, a new theory has suggested that the mightiest creatures may have succumbed to attacks by disease-carrying insects.

According to the theory profounded by Professor George Poinar of the Oregon State University and his wife Roberta, the demise of the dinosaurs and the rise and evolution of the insects, particularly the biting and disease-carriers, are linked to each other.

'We cannot say for certain that insects are the smoking gun, but we believe they were an extremely significant force in the decline of the dinosaurs. We also don't suggest that the appearance of biting insects and the spread of disease are the only things that relate to dinosaur extinction.

'Other geologic and catastrophic events certainly played a role. But by themselves, such events do not explain a process that in reality took a very, very long time, perhaps millions of years. Insects and diseases do provide that explanation,' the ScienceDaily quoted Prof Poinar as saying.

The couple have entailed their concept in a recently released book What Bugged the Dinosaurs? Insects, Disease and Death in the Cretaceous.

In the Late Cretaceous, Prof Poinar explained that the world was covered with warm-temperate to tropical areas that swarmed with blood-sucking insects carrying leishmania, malaria, intestinal parasites and other pathogens, and caused repeated epidemics that slowly wore down dinosaur populations.

'Smaller and separated populations of dinosaurs could have been repeatedly wiped out, just like when bird malaria was introduced into Hawaii, it killed off many of the honeycreepers. After many millions of years of evolution, mammals, birds and reptiles have evolved some resistance to these diseases.

'But back in the Cretaceous, these diseases were new and invasive, and vertebrates had little or no natural or acquired immunity to them. Massive outbreaks causing death and localised extinctions would have occurred,' Prof Poinar said.

In similar fashion, the researchers have suggested that the insects would have played a major role in changing the nature of plant life on Earth -- the fundamental basis for all dinosaur life, whether herbivore, omnivore or carnivore.

'As the dinosaurs were declining, their traditional food items such as seed ferns, cycads, gingkoes and other gymnosperms were largely being displaced by flowering plants, which insects helped spread by their pollination activities.

'These plants would have spread to dominate the landscape. Also, insects could have spread plant diseases that destroyed large tracts of vegetation, and the insects could have been major competitors for the available plant food supply.

'Insects have exerted a tremendous impact on the entire ecology of the Earth, certainly shaping the evolution and causing the extinction of terrestrial organisms. The largest of the land animals -- the dinosaurs -- would have been locked in a life-or-death struggle with them for survival,' say the authors.