Co-authored and photo by Abby Seaman and Mike Hoffmann of Cornell University.
The Trichogramma are a group of minute wasps (smaller than a needle’s eye) that lay their eggs in pest moth eggs, where the wasp offspring develop, kill the pest larvae, and produce new wasps. One species, Trichogramma ostriniae (TosTtm), was imported from China in 1990 and has been shown to be effective at controlling European corn borer, a serious insect pest of sweet corn, peppers, and potatoes. It may also hold potential against other pests such as cabbage looper, diamond back moth and grape berry moth.
When released in sweet corn fields, the tiny TosT wasps rapidly disperse and parasitize and kill European corn borer eggs. This process is repeated several times during the season, resulting in ongoing, season-long pest suppression. In some cases TosT is able to parasitize 80-100% of the European corn borer eggs. It is quite remarkable that a tiny wasp like TosT is able to search the huge surface area in a corn field and find European corn borer egg masses.
The current recommended release method for TosT is a single inoculative release (30,000/acre) at an early stage of corn development. In trials of inoculative releases in commercial fields of processing sweet corn, overall parasitism was about 50% over two years of trials. A more recent study has shown that a single release of 30,000 wasps per acre results in European corn borer control roughly equivalent to an insecticide application. Single inoculative releases in sweet corn clearly reduce infestations by the European corn borer and have been demonstrated to reduce the need for insecticide treatments — the intent is to suppress the pest not necessarily provide complete control.
More recently, trials have focused on three releases of 30-60,000 wasps per acre in the hopes of further improving control. Initial trials in a variety of other crops have been very promising. An early study showed the potential for controlling diamondback moth on cabbage. In that trial, 74% of diamondback moth eggs in a greenhouse were parasitized and 92% of eggs in an outdoor microplot were parasitized. In sweet pepper research in Kentucky, Virginia and Pennsylvania, TosT reduced European corn borer damage to peppers by 26-47%. In potatoes in Maine and Virginia, stem tunneling by European corn borer was reduced by about 60%.
For commercial production, Trichogramma wasps are reared on grain moth eggs. Once the grain moth eggs are parasitized, they are glued inside release packets that protect them from the elements and from predation by lady beetles and other predators. As wasps emerge from the grain moth eggs they leave the release packets and search out pest eggs. TosT can be stored for one to two weeks at about 48°F. In addition to prolonging its useful life, this tends to extend the duration of emergence so that not all adults emerge at once in the field. Mixing TosT of different ages in the release packets also extends the emergence period, assuring that female wasps are consistently out parasitizing pest eggs.
When released into sweet corn, most TosT remain in the field, but a few may disperse into other habitats where they may parasitize non-pest species. This potential impact on “non-target” species is real, but research to date indicates that the risk is minimal. Although Trichogramma wasps can parasitize the eggs of several species of moths and butterflies, in reality their host range is limited by their inability to find non-target eggs. While TosT is able to move into non-crop habitats, it appears to prefer corn when given a choice. It searches corn much more successfully than other plants. Recent studies suggest that TosT are attracted to European corn borer sex pheromones, but not by volatile chemicals coming from corn or pepper plants. So, although they may travel to habitats surrounding agricultural fields, the impact will be limited by their inability to find host eggs in non-agricultural habitats. In addition, TosT does not appear to survive the winter in the Northeast. When release sites are searched the following season, only a single incidence of overwintering has ever been found.
TosT is a natural enemy with a bright future. It has already proved its effectiveness against an important agricultural pest, and additional studies indicate it has potential against several others. Additional information including photographs is available. A fact sheet with instructions for releasing TosT will also be available in the winter of 2006/2007.
Thank you Jeffrey, Abby, and Mike.
