Rabdophaga rigidae

Mayetiola rigidae

Hosts: Salix discolor

Mayetiola rigidae attacks many species of willows. It has been reported from Salix discolor Miihl., S. humilis Marsh., S. rostrata Richards, S. cmdata Miihl., S. lucida Miihl., S. petiolaris Sm., and S. vimirzalis L.

The gall (Fig. 1) is monothalamous and develops by extensive hypertrophy of a willow bud. Galls are either apical or subapical depending on whether the affected bud is a terminal or lateral. First evidence of gall formation occurs when the developing bud becomes swollen; at this time several of the leaves have flushed and ring the upper part of the gall. When the gall matures, however, the leaves attending it die. Most of the leaves fall off, but occasionally one may persist for several months or over the winter. 

The mature gall is subglobular to fusiform and varies considerably in size and shape depending upon the host species and whether larvae are parasitized. Parasitized galls are small. Galls on S. discolor are larger than those on most other species. The size of galls observed in this study is indicated in Table I. 

Each mature gall terminates in a slender hollow beak with an open tip which leads to an interior chamber or cell where the insect develops. The gall is hard and woody. It is green during development but turns partly to completely red in the fall. A vacated subapical gall will continue to enlarge yearly as long as its supporting branch makes diameter growth. Occasionally, a gall on a short slender twig breaks off during the winter. Sometimes a small branch above a subapical gall dies and breaks off. 

Adults emerge from the galls soon after the first few warm days in April. Nearly all adults emerge in the morning between 0700 and 1200 hours on sunny days; the peak occurs between 0900 and 1000 hours. Males appeared first each year; females appeared 1-3 days later. The sex ratio in 1963 as determined from 85 reared adults was nearly 1 : 1. 

Eclosion starts within a few minutes after the pupa wriggles up the chamber and protrudes from the tip of the beak. About 3 minutes elapse between the time the pupal skin splits and the adult is dry. About 10 minutes after eclosion the meconium is ejected from the tip of the abdomen; it is usually released in several short bursts of fine droplets. Considerable walking up and down the stem follows. 

In mid-May, at the onset of the second instar, the gall is just discernible as a swollen leafy bud. By the time the insect reaches the third instar in early July the gall has attained over 85% of its growth but is still shrouded with green leaves. The gall rounds up, hardens, turns red, and drops most of the attending leaves during the first few weeks of the third larval stadium. 

Range: East Lansing, MI

Life history and habits of the willow beaked gall midge, Mayetiola rigidae (Diptera: Cecidomyiidae), in Michigan