OTTAWA - A horde of insidious insects has been poisoning crops and using the drought to cover the crime, agricultural experts say.

Potato leafhoppers, usually rare in Ontario, are ravaging alfalfa crops.

Not content to merely feed on the alfalfa's juices, the 3mm-long sap-suckers actually inject toxic saliva into the plants, which inhibits their circulation system.

"The sap becomes sort of gelatinous and it doesn't flow," provincial field crop specialist Gilles Quesnel said.

The internal damage is tough to spot at first, allowing the leafhopper population to explode undetected.

And the drought has given leafhoppers an extra edge since they swept up from the southern United States -- not only has the hot weather spurred insect intercourse, it has also made farmers more likely to the blame lack of water for stunted crops.

"It's been dry, but for the alfalfa crop, the biggest impact has been this insect," Quesnel said. "Because it's not an insect that we have as a problem every year, growers, their normal tendency is to think that it's drought that's the problem."

"It's been hard to get the word across."

In fact, alfalfa's deep-reaching roots make it less vulnerable to drought, preserving it for the destructive green bugs.

The economic impact will be severe.

Because the insect has flown under the radar for so long, Quesnel estimates about 30% of the alfalfa crop may be lost this year, a loss of about $150 to $200 per acre.

Last year, farmers harvested over 1.1 million tonnes of hay from 622,000 acres of land in Eastern Ontario alone -- about 1/5th of the province's hay production, according to Ministry of Agriculture data.

"Only once in a while do we see economic damage from (leafhoppers)," Quesnel said. "Here, basically all the alfalfa crops across the province have been hit by that insect."

Used as cattle feed, scarce alfalfa means pricy alfalfa -- and in turn big bucks for beef.

To beat the insects, Quesnel suggests cutting the alfalfa down -- farmers routinely harvest the fast-growing plants two or three times a season -- to eliminate the damaged bits and to give the insects nowhere to hide.

Pesticide, normally not used, is required to finish the job.

Wetter weather and dewier mornings will also lower their population.

The frost will finish them off and next year, with any luck, there will be less hot air for them to ride up north.