CYNIPID-INDUCED GALLS and CALIFORNIA OAKS by K.N
Total Page：16
File Type：pdf, Size：1020Kb
$10.00 (Free to Members) Vol. 30, Nos. 3-4 July/October 2002 FREMONTIA A JOURNAL OF THE CALIFORNIA NATIVE PLANT SOCIETY IN THIS ISSUE: INTRODUCTION by G.W. Frankie / 3 • LEPIDOPTERAN CATERPILLARS FEEDING ON CALIFORNIA NATIVE PLANTS by J.A. Powell / 5 • CYNIPID-INDUCED GALLS AND CALIFORNIA OAKS by K.N. Schick / 15 • BARK BEETLES INFESTING CALIFORNIA’S CONIFERS by D.L. Wood and A.J. Storer / 19 • BUMBLE BEES: BOISTEROUS POLLINATORS OF NATIVE CALIFORNIA FLOWERS by R.W. Thorp, P.C. Schroeder, and C.S. Ferguson / 26 • A PINNACLE OF BEES by O. Messinger and T. Griswold / 32 • NATIVE BEES, NATIVE PLANTS, AND CROP POLLINATION IN CALIFORNIA by C. Kremen, R.L. Bugg, N. Nicola, S.A. Smith, R.W. Thorp, and N.M. Williams / 41 • BEES IN BERKELEY? by G.W. Frankie, R.W. Thorp, M.H. Schindler, B. Ertter, and M. Przybylski / 50 • FARMSCAPE ECOLOGY OF A VOLUMENATIVE 30:3–4, STINK BUG JULY/OCTOBER IN THE SACRAMENTO 2002 VALLEY by L.E. Ehler, C.G. Pease, FREMONTIA and R.F. Long /1 59 • ENDANGERED PLANTS AS GUIDES FOR SAVING ENDEMIC INSECTS IN CALIFORNIA by D. Rubinoff / 62 • NOTES AND COMMENTS / 67 • BOOKS RECEIVED / 70 • BOOK REVIEW / 70 Oak apple gall (Andricus quercuscalifornicus) on valley oak (Quercus lobata). Photograph by G. Frankie. CYNIPID-INDUCED GALLS AND CALIFORNIA OAKS by Kathy Schick atching a tiny female Suddenly, a gust of wind sweeps ing plant growths called galls, filled WAndricus fullawayi wasp the tiny wasp into the branches of a with nutritive tissues. The galls through a magnifying nearby valley oak (Quercus lobata) provide food and shelter for the glass, I am amazed at the amount of and she is lost to sight. I wonder developing larvae of the wasps. time she spends carefully grooming where this tiny creature is going, Oak gall wasps are members of her wings and antennae with the and whether her offspring will de- the insect order Hymenoptera, fam- special combs on her front legs. As velop within a gall on the stem, leaf, ily Cynipidae, and tribe Cynipini. I wait anxiously to see where she flower, or root of an oak tree. Unlike bees, ants, and stinging will fly to lay her eggs, she crawls Like many other cynipid wasps, wasps, in which the ovipositor has awkwardly, brushing her antennae this tiny, ungainly female is smaller evolved into a stinger, cynipid wasps against the twig to test its odors. than this typeset number “1,” yet have retained ovipositors with which She takes her time. More than 20 she and other gall wasps have man- they can carefully position their eggs minutes elapse after I release her aged to colonize every native oak inside plant tissues without harm- from the rearing container before tree species in California. They trick ing any plant cells. she finally becomes airborne. their host trees into forming strik- The most primitive living VOLUME 30:3–4, JULY/OCTOBER 2002 FREMONTIA 15 relatives of modern cynipid wasps Figitidae, which parasitize the lar- tain more than one larva such as use their long ovipositors to lay eggs vae of flies; lacewings and other the large “oak apple” gall induced into the larvae of wood-boring wasps; and Cynipidae. on Quercus lobata by the wasp wasps and beetles, much as their Apparently early in their evolu- Andricus quercuscalifornicus (see pho- earliest ancestors probably did. tionary history, ancestors of cynipid tographs, page 15). This stem gall From such primitive ancestors two wasps began to skip the insect host gets as big as a baseball and may modern families of wasps evolved: and consume plant tissue directly contain as many as 16 developing through gall induction. The oldest larvae. The galls generally start Wasp of Andricus quercuscalifornicus known fossil cynipid galls, approxi- forming in early spring and grow (top) on gall. Photograph by K. Schick. • mately 115 million years old, are into round green spheres that re- Spindle gall (bottom), unisexual gen- found in Cretaceous deposits. semble juicy green apples, even to eration of Heteroecus pacificus, on Quercus vaccinifolia (huckleberry oak). Photo- Regular readers of Fremontia will the point of developing a reddish graphs by K. Schick. be familiar with some of the exotic blush when they mature. The color and bizarre shapes of modern quickly fades and the drying galls cynipid galls on blue oak (Quercus turn beige during the summer. The douglasii) from the excellent photo- wasps within finish pupation and graphs in an article over a decade emerge as adults in autumn, leav- ago by Russo (1990). Each species ing the gall behind on the tree. of cynipid wasp induces its oak host After the first year, old galls turn to form a unique shape of gall. black, covered in sooty mold. While many other gall-inducing insects, such as tenthridinid wasps, inject chemicals into plant tissue ALTERNATION OF along with their eggs so that gall GENERATIONS formation begins before larvae emerge, gall induction in Cynipidae Distinctly different galls—often begins in response to chemicals se- on different parts of the host tree— creted by growing wasp larvae. are produced not only by different Cynipid galls are more com- wasp species, but also by different plex than galls of many other in- generations of the same cynipid spe- sects. They contain several tissue cies. Most cynipid species in the layers and a separate central cham- oak-galling tribe Cynipini have two ber for the developing larva. alternate generations each year: a Cynipid larvae complete their de- bisexual generation with both males velopment by becoming pupae and and females developing in spring then adults, before they emerge galls, and a unisexual generation of from their galls to lay eggs for the only females in autumn galls. This next generation. phenomenon of alternating genera- Galls may contain a single larva, tions is called heterogony and results as do those of the jumping gall in females so different from those Neuroteras saltatorius, a tiny spheri- of their alternate generations that cal structure about the size of this many were originally described as “o” which forms on the underside separate species, sometimes even in of oak leaves. These tan-colored separate genera. galls hop up and down under Quercus The unisexual generation of the lobata oaks from June through Au- wasp Antron douglasii produces strik- gust in the Central Valley of Cali- ing pink star-like spiny turbans in fornia. The dropping galls jump summer on the leaves of Quercus around for a while after they fall lobata, Q. dumosa (Nutall’s scrub from the leaves, eventually maneu- oak), and Q. douglasii. The bisexual vering themselves into crevices in generation of this wasp produces the ground where they will endure twig galls that look like large white the winter, and from which the adult semi-translucent mistletoe berries females will emerge in early spring. in early spring, later fading and Other cynipid galls may con- hardening to woody knobs. Wasps 16 FREMONTIA VOLUME 30:3–4, JULY/OCTOBER 2002 for the remaining cynipid species lay their eggs. When inquiline lar- in California will require a lifetime vae emerge they may consume all of study. the nutritive cells, starving the gall- inducer. Some species may even deliberately kill the gall-inducing A COMMUNITY OF larva in order to consume its food WASPS IN AN OAK resource. GALL A very few cynipid inquilines actually induce changes in the shape At first glance, an oak gall might of the gall, indicating that they have seem an ideal refuge from preda- not entirely lost the ability to se- tors and other dangers to young crete appropriate chemicals. One larval insects. Oak galls are espe- such inquiline species in the genus cially rich in tannins, much more so Synergus causes unisexual galls of Jumping gall, the unisexual generation of Neuroterus saltatorius, under Quercus than normal plant organs, so the Heteroecus pacificus forming on ei- lobata leaf. Photograph by G. Frankie. gall tissue should not be especially ther Quercus chrysolepis (canyon oak) attractive to plant-eaters. However, or Q. vaccinifolia (huckleberry oak) emerging from these spring galls these galls cannot move so they are to change from a narrow spindle were first placed in the genus predictable food resources, attract- shape to a rounded globular shape. Dryophanta because they looked so ing herbivores as well as insect-eat- I have dissected these galls and strikingly different from their al- ers. Also abundant in oak galls are found as many as five larval cham- ternate generation. two other groups of wasps: herbivo- bers for the smaller inquiline wasps Surprisingly, even though their rous inquiline (“guest”) cynipid around a single central chamber for homes are so distinctive and thus wasps and very specialized parasi- the larger gall-inducer, all of which the insects should be easy to locate, toids in the superfamily Chalci- scientific knowledge of the gall wasp doidea. fauna in California is far from com- The inquiline wasps all belong plete. Many oak galling species have to the tribe Synergini within the yet to be described, and alternate family Cynipidae and appear to have generations are currently known for lost the ability to secrete gall-in- fewer than a fourth of the 122 de- ducing chemicals. Instead, they lo- scribed California species. cate developing galls into which they In the British cynipid fauna, which is well known, some cynipids Oak apple gall (Andricus quercuscali- species are known to have alternate fornicus) (right), on valley oak (Quercus generations on separate oak tree lobata). • Three galls on leaf of Quercus lobata (below): clockwise from tip, Antron species, as well as strikingly differ- douglasii, Besbicus conspicuous, and ent morphologies and colors with Xanthoteres clavuloides.