Hoplocampa crataegi

3.5 to 5.5 mm.  Very variable in colour but often predominantly pale orange above and below. However, the metanotum sutures are black in both males and females.

Unless identified by a recognised expert, a photo is required. If the photo doesn't show the key ID features, then in the comments box describe the size and identifying characters you have observed.

Associated with Hawthorn.

May to June.

Females cut and lay eggs into the ovary behind hawthorn blossoms. The larva feeds inside the developing fruit. The damaged fruit will drop before maturing, at which point the larva leaves the fruit and pupates underground. Larvae may migrate to a second fruit.

Locally fairly frequent, especially in the southern half of Britain.

Status in Leicestershire and Rutland not known.

https://www.sawflies.org.uk/hoplocampa-crataegi/