onion crops are vulnerable to a virus known as Iris yellow spot virus (IYSV), which they acquire from insects called onion thrips (Thrips tabaci). IYSV causes necrosis in onion plant tissues and leads to millions of dollars of crop losses each year.

Thrips can pick up the virus from infected onion plants when they are larvae, and, once infected, they can spread the virus to other onion plants throughout their lives. Previous research discovered that infection with plant viruses in the genus Tospovirus increased lifespan and fecundity in a different species of thrips called flower thrips.

A Cornell research team, led by graduate student Ashley Leach, along with colleagues Marc Fuchs, Ph.D., Riley Harding, and advisor Brian Nault, Ph.D., compared the lifespan and fecundity of onion thrips that were infected with the virus with thrips that were not infected. To do so, they gathered onion plants from fields in which IYSV was present, maintained the plants in the lab, and exposed thrips to the onion plants so that they could pick up the virus and lay eggs.

They then allowed the resulting eggs to develop to pupation. They removed pupae and placed them on discs of cabbage leaf as a growing medium. When onion thrips emerged from pupation, the researchers monitored their survival and reproduction every 24 hours throughout their lifespan. All thrips in the experiment were female, and their eggs developed into larval thrips parthenogenically (without fertilization).

One hundred and forty-nine thrips were used in the experiment. The investigators determined whether or not individual thrips had become infected with IYSV by testing for presence of a IYSV nucleoprotein gene using a technique known as reverse-transcriptase polymerase chain reaction. Previous studies did not determine whether thrips were infected with tospoviruses; by determining infection status, Leach and colleagues created greater statistical power than was available in previous work.

Of the 149 thrips tested, 77 percent were infected with IYSV. The investigators found that thrips infected with IYSV lived 3.6 days (or 22 percent) longer on average than uninfected thrips. They found no significant difference in fecundity, however, between infected and uninfected thrips. The results of the study were published in late May in the open-access Journal of Insect Science