The wheat stem sawfly (Fig. 1) is thought to be native to North America and is found throughout the brown soil zone of the Great Plains. First noticed in Canada in the late 1800s, the wheat stem sawfly was considered an agricultural pest by the early 20th century. Spring wheat is the preferred host for this insect, however, recent reports from Alberta and especially Montana indicate that some varieties of winter wheat are also suitable hosts for this pest.
Many producers consider the wheat stem sawfly to be a problem only in field margins. Although crop injury by the wheat stem sawfly is usually more prevalent within the first 20 metres of the field edges, damage is not confined to the margins. In many of the recent sawfly infestations, entire fields have been affected, some with estimates of more than 70 per cent of the stems cut.
Economic loss due to the wheat stem sawfly may be a reduction in yield and/or grade as a result of larval feeding within the stem. Estimates suggest a five to 15 per cent decrease in total seed weight. The biggest loss, however, is from the stems being cut and plants falling to the ground, making pick-up for harvest extremely difficult.
The wheat stem sawfly was not a significant pest for a number of years. Dry weather cycles and tight wheat rotations are the primary factors contributing to increased sawfly populations. Warm, sunny, calm weather following spring rains will result in wider dispersal of the insect within a field or to adjacent fields. Excessively wet conditions tend to be detrimental to both sawfly and parasite populations and activity. In the absence of severe sawfly pressure, producers tended to choose wheat varieties that offered attributes such as increased yield, protein and disease resistance rather than sawfly resistance. To some degree, the adoption of conservation tillage practices that leave stubble containing sawfly larvae intact may also favour increased wheat stem sawfly populations.Click here to see more...