A little about Gall Wasps
Disholcaspia prehensa Clasping Twig Gall, Cynipid wasp
Plant galls are produced in response to mechanical and/or chemical stimuli of the invading organisms. In many of these cases the gall is a nursing site for the offspring of mites, psyllids, aphids, wasps and other insects. Galls are nutrient sinks, that is, food for plant growth is redirected into gall growth. There is no known benefit, such as the wasps feeding on aphids and other small insects that are likely to be found feeding on the host tree. Adult gall wasps only live for a week or two after emergence and do not feed during that period of their life.
Antagonistic insects (bees, yellow jackets and ants) are drawn to some galls because of the gall’s production of honeydew. Cynipid wasps, such as the Clasping Twig Gall Wasp (see photo above), Acorn Gall Wasp and the Round Honeydew Gall Wasp all stimulate the production and release of sweet phloem exudates. This honeydew attracts bees, ants and yellow jackets that attack other species of insects attracted by the sweet substance. This makes it almost impossible for parasitic wasps and others to invade the galls. This honeydew is an important food source for the yellow jackets and ants in late summer and fall.
Live Oak Petiole Gall Wasp and Eumayria eldoradensis, both cynipid wasps, attack immature acorns of live oak species. Adult wasps puncture the acorn to lay eggs. A bacterium, Erwinia quercina, enters the acorn through these holes. After a bit an ooze develops and begins dripping. Without the bacteria the gall wasp activity would not be noticed. The effect of the bacterium on the gall wasp eggs is unknown.
INTERESTING ADDITIONAL FACTS
• Some cynipid wasps remain in diapause (prepupil sleep) for a year or more before completing metamorphosis into adults.
• Many species of cynipid wasps have two alternating generations that cause different galls on different plant parts at different times of the year. This is known as Heterogeny. Typically there are two modes of reproduction. The spring generation is made up of males and females and reproduces sexually. The summer-fall generation is typically female only (Parthenogenesis) that results in next year’s spring galls bearing males and females. There are many gall insects where there are no known males in the population.
• Galls may occur on leaves, stems and branches and may be caused by rust fungi, mistletoe, flies, moths, beetles and wasps. World wide there about 13,000 species of gall-inducing arthropods. In the U.S. there are over 2,000 known species and of that about 1,000 of them are cynipid wasps.
Disholcaspis plumbella Beaked twig gall wasp
Observed on Quercus durata, trail 15 near the intersection with trail 16.
Oval/round and peaked at one end. Monothalmous. Rusty red with yellow spots. I cut one open to reveal the central larval chamber. One larva observed. Collected three on twigs with hope to observe adult wasp. Search of web sites disclosed no photos of this particular wasp adult.
See also: Plant Galls of the California Region by Russo.
Observed and photographed (photo 1) another gall on Q. durata, Disholcaspia prehensa; The Clasping Twig Gall. There was evidence of phloem sap being attended to by a few reddish ants.
Cynipid wasps are the most common gall wasps in California. The larva secretes enzymes that convert plant starch into soluble sugar which the larva feed on. Cynipids have a dead-end intestine and, therefore release no fecal matter until diapause.
Photos by author
Bob Dodge
March, 2007
Comments
Very interesting. I had wondered what sorts of insects were responsible for galls. So its mostly cynipid wasps but several other insects also do this? Do you know what may have formed this gall?
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