How damaging are wheat lemon blossom midges?

When it comes to wheat blossom midges, it’s the orange one that gets all the limelight. However, we should pay more attention to its yellow cousin, the lemon blossom midge, according to trial data analysed by Paul Gosling.

Although the lemon blossom midge (Contarinia tritici) looks like the orange blossom midge (Sitodiplosis mosellana) (Figure 1), it arrives earlier and damages crops differently.

Lemon blossom midge larvae feed on the flowers, preventing pollination and reducing yield. Whereas orange blossom midge larvae feed on developing grain, reducing yield and quality.

Figure 1. Orange wheat blossom midge (left) and lemon blossom midge (right)

Varietal resistance is another major difference. There is a well-characterised mechanism that gives wheat resistance to the orange blossom midge. Over 60% of the current (2022/23) AHDB Recommended Lists (RL) wheat varieties are believed to resist this pest (although this is not verified in RL tests). Conversely, there is no known resistance to the lemon blossom midge.

Generally, the lemon blossom midge is thought to be less of a problem. However, there have been increasing reports of this midge over the last few years.

The potential for lemon blossom midge to impact yields was captured at an RL winter wheat trial in the 2021–22 season.

The second winter wheat trial was drilled on 9 October 2021 at a site in the Yorkshire Wolds. It got off to a strong start and was in good condition in the spring. However, when the trial was inspected in the summer (21 July 2022), there was clear evidence of lemon blossom midge damage (Figure 2).

Figure 2. Lemon blossom midge damage to winter wheat ears at an RL trial site (north Yorkshire, July 2022)

Each wheat plot was scored for lemon blossom midge damage using a 1–9 scale, where one represented no damage, and nine indicated the highest level of damage.

In this trial, we charted the plot-by-plot yields (ignoring variety) against the lemon blossom midge damage score (Figure 3). This showed a weak but statistically significant relationship, which suggested that high damage (9), compared to no damage (1), equated to around a 1.7 t/ha yield loss.

Figure 3. Relationship between lemon blossom midge damage scores and plot yields (blue dots) at an RL trial site (north Yorkshire, harvest 2022)

We also charted how the variety means (as a percentage of the controls) in the lemon blossom midge damaged trial deviated from the variety means (as a percentage of controls) of the whole trials set in 2022 (Figure 4).

Fortunately, in the affected trial, most control varieties suffered low levels of damage (scored 1 or 2). However, some control plots were affected more and removed from the control mean for this trial: two plots of KWS Barrel (scored 4) and one plot of KWS Siskin (scored 6).

This analysis revealed a highly significant relationship. Some of the most damaged varieties suffered yield losses greater than 20%, compared with what was observed in the full trial set.

In this analysis, the yield loss in highly damaged (scored 9), compared to undamaged varieties (scored 1), was equivalent to 2.14 t/ha.

Figure 4. Relationship between varieties’ lemon blossom midge damage scores (north Yorkshire, harvest 2022) and the deviation of the variety trial yield means (blue dots) from the whole-trial-set mean (set at 0), excluding the affected trial

Both analyses indicated a significant relationship between lemon blossom midge damage and yield. Although the results were not the same, both estimated similar yield penalties associated with the most severe damage (around 2 t/ha). Despite being based on a single site in a single year, these similar results give some confidence in the overall analysis.

The differences in varietal performance recorded are likely to reflect variations in crop growth stage when the midge attacked. As mentioned, there is no known genetic resistance to this midge. Wheat breeders continue to investigate potential resistance sources. However, even if resistance were incorporated, elite varieties with such a trait would be several years away from the market.

While orange wheat blossom midge remains the greater threat to winter wheat, the analysis from this trial suggests that lemon blossom midge can have a significant negative impact on yield, when present.