Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae)

Distribution

Ostrinia nubilalis is native to Europe and was introduced into North America near Boston (Massachusetts) in 1917 (Baker et al. 1949). It gradually spread from there to other parts of the United States and Canada.

It has also been reported in Asia (China, India, Georgia and Indonesia, middle East (Syria, Israel, Lebanon, Iran, Turkey) and North Africa (Algeria, Egypt, Libya, Morocco and Tunisia) (EPPO 2014; Li et al. 2003). Two races, E and Z that are morphologically indistinguishable exist in both USA and Europe.

Host range

The European corn borer is primarily a pest of maize (Zea mays L.), but very polyphagus feeding on host plants from over 17 families but not necessarily being a pest. Economic host crops include potato, pepper, celery (Apium graveolens L.), tomato, beans, hop (Humulus lupulus L.), oat (Avena sativa L.), millet (Panicum spp.), sorghum (Sorghum bicolor L. Moench), cotton (Gossypium arboreum L.), and fruits such as apple (Malus pumilla Miller) and peach (Prunus persica (L.) Batsch L.).

Feeding also occurs in ornamental plants and weeds including hollyhock (Alcea rosea L.), mugwort (Artemisia vulgaris L.), pigweed (Amaranthus spp.), and others.

Symptoms of infestation

In potato, the most obvious sign of infestation is stem wilt. The entrance hole is in the stem and is easy to locate because of the presence of the excreta that larvae expel while feeding inside the stem. Larval presence can be confirmed by cutting the stem (CABI 2017b).

Young larvae tunnel into leaf petioles while older larvae tunnel into the main stem. Larval damage can, however, be confused with that of other stem borers.

Impacts on production losses

Potato plants present high tolerance for this insect; fairly high levels of infestation often do not seem to significantly affect tuber yields (Kennedy 1983). Varieties with weak stems are more likely to suffer reduced yields, as affected stems will break more easily during heavy wind- or rain- storms.

However, severe infestations may result in considerable crop losses. Also, larval entry holes may facilitate infection by fungal and bacterial pathogens such as Erwinia carotovora.

Methods of prevention and control
 

• Sampling.
  Monitoring of adult moth flights is suggested to determine the timing for oviposition and hence if a field is at risk. Sticky traps baited with strain-specific sex pheromones can be used for this purpose.
  
  Early infestations can also be more damaging than later ones and scouting for egg masses and observation of damage by the first instar larvae on leaf petioles. It is prudent to be vigilant and to monitor populations in areas where this insect has been known to previously cause damage.


• Cultural control.
  This can involve early planting to escape damage, intercropping with nonhost plants and proper field sanitation involving of ploughing the field at the end of the cropping season.


• Chemical control.
  European corn borer larvae are not particularly difficult to kill, but pesticide applications, to be effective, must be made before the larvae enter the stem. Pesticide application is recommended only when more than 10% of the stems show evidence of tunneling (Nault and Kennedy 1996).


• Biological control.
  Bacillus thuringiensis subsp. kurstaki (Btk) and B. thuringiensis aizawai can be successfully applied to target first instar larvae. Alternative control methods include release of commercially available parasitic wasps (Trichogramma nubilale Ertle and Davis and T. brassicae Bezdenko) (CABI 2017b).
  
  Other natural enemies that have been used to control the European corn borer include Lydella thompsoni (Herting), Diadegma terebrans (Gravenhorst) and Macrocentrus grandi Goidanich (Baker et al. 1949).