An invasive pest that has ravaged the southeast is threatening California's $2 billion citrus crop.

"It is a tiny little plant-feeding insect, kind of like an aphid. And the problem isn't this insect so much, but a bacterial disease," Lynn Kimsey, a UC Davis professor of entomology said. 

Kimsey says the bug called, the Asian citrus psyllid, transmits a tree-killing disease called citrus greening.

"A tree that's infected with this disease, basically, you have to take it out," she said. 

Farmers across the state are worried about the psyllid and disease, but Kimsey says there is hope.

"In California, so far, we have not gotten the disease here yet," she said. 

The state and federal governments are now fighting the insects with insects, unleashing wasps from Pakistan that lay their eggs under the psyllids.