Factors affecting grain aphid movement with reference to spread of BYDV in the autumn and winter and forecasting direct damage in the summer

Abstract

Grain Aphid Movement with Reference to Spread of BYDV in the Autumn and Winter

1. Movement of introduced aphids and spread of BYDV in barley during the winter were assessed on small plot field experiments. Results suggested that movement by the grain aphid under cold winter conditions was greater than that by the bird-cherry aphid, probably due to greater survival.

2. Laboratory studies to investigate abiotic factors which affect movement of wingless aphids showed that under conditions of constant wind, the distance moved by aphids increased with time; conditions of strongly gusting wind increased the proportion of aphids leaving a plant and the distance moved by them; aphid dispersal increased with rain intensity, droplet size and temperature.

3. Laboratory studies to investigate biotic factors which affect movement by wingless aphids showed that high aphid density was a strong stimulus for dispersal; at a plant spacing greater than 8 cm aphids were less likely to leave a plant; adult aphids were more likely to leave a plant and move further than nymphs; in glasshouse conditions a greater proportion of bird-cherry aphids moved than did grain aphids. When compared with field experiments above, the latter result suggests that environmental conditions may have a key role to play in the relative contribution to virus spread made by each species.

4. A comparison was made of the number of asexual grain aphids caught during the autumn in six types of trap at Starcross and Leeds. None of the trapping methods was an improvement on the 12.2 m or the 1.5 m suction traps.

5. Two synthetic aphid sex pheromones were assessed for their potential to monitor the sexual portion of the grain aphid population. The mixture of nepetalactol and nepetalactone was a strong attractant for male aphids.

Grain Aphid Movement with Reference to BYDV in the Spring and Direct Aphid Damage in the Summer

1. An investigation of the spread of virus by wingless aphids in spring-sown cereals showed that adults accounted for a greater proportion of virus spread than did nymphs, and that populations of wingless aphids on a crop may make a significant contribution to the spread of virus in the spring.

2. A field experiment showed that early-sown spring crops are at less risk of BYDV infection than late-sown crops and that the effectiveness of sprays aimed at controlling virus depends on the level of virus present in nearby overwintering crops, as well as the timing of aphid migration relative to crop development.

3. Overwintering aphids on winter wheat make a major contribution to the total size of aphid populations on the crop in the spring, particularly early in the season. A spray in March removes this problem. Sprays applied at the beginning of aphid immigration were not effective. A spray at or just after growth stage (GS) 73 was effective in reducing peak numbers of aphids in the crop during the two years under study. The effectiveness of this spray may vary from year to year.