Southern Europe and Northern Africa
Field bindweed (Convolvulus arvensis)
All stages of this species are difficult to see and are best viewed through a microscope. Eggs are spherical and white. While adults of many other mite species have eight legs, A. malherbae nymphs and adults have only two pairs of legs; these are located near their heads and have feather claws at their tips. Nymphs and adults are elongated with whitish-yellowish, translucent bodies. First-instar nymphs are smaller and have reduced features, while second-instar nymphs are similar to adults but lack a genital opening.
As field bindweed resumes growth in early spring, mites feed on developing leaf tissue and stem tips, leading to the formation of contorted galls along leaf midribs. Females lay eggs within gall tissue, and there are two nymphal stages prior to the adult stage. One generation can be completed in 10–14 days, depending on temperature, and there are multiple generations per year. As field bindweed vines die back in autumn, mites migrate down to field bindweed root buds where nymphs and adults overwinter. Throughout the growing season, mites primarily spread via wind, although some are also carried on the bodies of visiting insects.
Galls induced by mite feeding create a characteristic deformed appearance of discolored and folded growth along leaf midribs and around root crowns. Mite feeding and gall formation stunt the growth of attacked stems, form clusters of twisted and shriveled leaves, and reduce or eliminate flowering and corresponding seed production.
Andreas, J.E., J. Littlefield, J. Milan, and A. Mendenhall. 2024. Field Bindweed Biocontrol Agents: History and Ecology in North America. In: R.L. Winston, Ed. Biological Control of Weeds in North America. North American Invasive Species Management Association, Milwaukee, WI. NAISMA-BCW-2024-10-FIELD BINDWEED-A. https://bugwoodcloud.org/resource/files/31490.pdf