‘Concord’ grape cluster showing extent of GSC infestation. Arrows point to

adult chalcid exit holes that can be seen Seed chalcids destroyed between

70% and 100%of grapes on the backyard plant in each of the past three

years. The uneven ripening is due to the early veraison growth stage, and is

independent of the seed chalcid infestation.

Grape seed chalcid damage appears as a round exit hole about 1.5 mm in

diameter. The wasp chews its way out of the seed and through the skin.

Damaged grapes shrivel and fall from the cluster. Damaged berries that do

not drop are susceptible to rots.. Damage appears, and adult emergence oc-

curs during August in western Colorado.

Acknowledgements John Carls allowed access to his yard and garden in Montrose

CO. He sacrificed a few gallons of homemade wine to allow

our observations. Horst Caspari contacted TRA Extension with

the original damaged grape sample and has provided viticul-

tural advice and assistance from his position at the Western

Colorado Research Center. Bryan Braddy found and collected

grape seed chalcids from the research vineyard at Rogers

Mesa CO. Boris Kondratieff assisted with identification of the

specimens. Melissa Franklin assisted in all phases of collec-

tion, literature search, and producing this poster.

According to the limited literature on grape seed chalcid, egg laying occurs

while the grapes are still quite hard, pre-veraison. Crosby 1909a says the

eggs are inserted in the chalaza of the hard seed. Larvae hatch, chew their

way into the seed, then feed on the endosperm. More than one seed per

berry can be infested. This shows the exit hole in the seed and grape skin

made by the emerging adults.

This newly emerged adult chalcid was found within a normal appearing,

but internally damaged seed. The larval entry hole into the seed is not

readily noticeable. Apparently, damage from the two species of chalcids

that feed on seeds of Vitaceae is similar.

Adult wasps were reared from infested grapes. They are approximately 4

mm long. Female wasps have larger abdomen and shorter petiole than

males. The distinctive antennae was a useful characteristic to separate P.

cooki from other chalcid species on yellow sticky traps.

♂

♀

Observations from the field:

Grape seed chalcid was found damaging ‘Concord’ grapes, Vitis labrusca and Virginia

creeper, Parthenocissus quinquefolia in a back yard home garden setting in Montrose, Colo-

rado (Montrose County) in 2011. A second grape seed chalcid infestation was identified in

September 2013 in ’Aromella’ grape near Hotchkiss, Colorado (Delta County).

Damage appears as a small round exit hole in the skin of grapes that had colored but were not

yet mature. Cut fruits show insect feeding damage within one or more seeds in each infested

berry. Damaged seeds have an exit hole in the pericarp and feeding within the endosperm.

At the Montrose site, there were three ‘Concord’ grape vines, of which the same one was in-

fested each year. More than 70% of berries on that vine were infested while berries on nearby

vines were not. Distribution on Virginia creeper followed the same pattern as on grape. Individ-

ual vines were either heavily infested or not at all infested.

Yellow sticky traps were placed in the canopy area of both grape and Virginia creeper at the

Montrose site in 2012 and 2013. They were checked and replaced at approximately 2 week in-

tervals. Other species of chalcids were captured on all traps, but P. cooki was only captured in

August 2012 traps. This coincided with emergence of adult wasps in the lab from field col-

lected grapes, and the appearance of exit holes in grape berries in the garden.

Summary: Grape seed chalcid has been a minor pest of grapes in North America for almost 150 years

and there is no reason to suspect it will ever be anything other than that. It does have potential

to impact isolated small plantings of susceptible grapes.

Grape seed chalcids are probably more common than one would suspect. Individuals involved

with garden grapes or commercial vineyard management should become familiar with this in-

sect and its damage symptoms.

There are two species of grape seed chalcid. Prodecatoma cooki is widespread but rare within

its geographic range, with reports from Canada to Venezuela. There is no mention of Evoxy-

soma vitis in the scientific literature since 1924. It has disappeared.

There is limited literature on the biology, behavior and host preferences of either species. The

bulk of the current knowledge base is from late 19th and early 20th century publications. Re-

cent publications document the occurrence of P. cooki in Mexico and Venezuela.

Our observations show, and the literature agrees that P. cooki has definite host preferences,

feeding only on certain genetic types of grapes and Virginia creeper. The common factor of ac-

ceptable host varieties is unknown.

Prodecatoma cooki (Howard)

in Western Colorado Bob Hammon, Colorado State University, Tri River Area Extension

Literature Review: A search of literature published on grape seed chalcid reveals two species of seed chalcids that

attack grapes. Evoxysoma vitis (Saunders) was originally described in Saunders 1869, with life

history observations in Crosby 1909a & b. Crosby 1909a describes a second species of seed in-

festing chalcid, Prodecatoma phytophaga, from Virginia creeper. Gahan (1924) recorded the

first account of P. phytophaga feeding on grapes. He recognized that there were actually two

distinct species of chalcid that fed on vitaceae seeds. His mention of E. vitis is the last mention

of this insect in non-taxonomic scientific publications. He recognized synonymy of P. phyto-

phaga and Decatomidea cooki (Howard) in his 1951 publication and renamed the species to

Prodecatoma cooki (Howard). Adlert documents P. cooki in Florida grapes in two 1973 publi-

cations. It has been reported from Canada, several US states, Venezuela (Cermeli 1973) and

Mexico (Cortez-Madrigal et al. 2012).

Saunders, W. 1869. The grape-seed insect. Canadian Entomologist 2:25-27

Bethune, C.J.S., W. Saunders, & ; E. B. Reid. 1871. First Annual Report on the Noxious Insects of Ontario. Entomol Soc Canada. Hunter, Rose &

Co, Toronto Canada. 138p.

Howard, 1896. Decatomidea cooki How. U.S. Dept Agr. Div. Ent. (Tech. Ser.) Bul. 2, p. 25

Crosby, C.R. 1909a. On certain seed-infesting chalcis flies. N.Y. (Cornell) Agric. Exp. Stn. Bull. 265:382-5

Crosby, C. R. 1909b. Two new seed infesting chalcis-flies. Can. Entomol. 41: 50-55.

Gahan, A. B. 1924. Another Seed-Chalcid attacking the Cultivated Grape. Proceedings of the Entomological Society of Washington; 26 (2), Wash-

ington, D.C., p48.

Gahan, A.B. 1951. Some synonymy and new combinations in Chalcidoidea (Hymenoptera) Can Entomol. 83:170-176

Alderz, W.C., & J.A. Mortensen. 1972. Seed chalcid damage, distribution, and control on central Florida bunch grapes . Florida Agricultural Experi-

ment Stations Journal Series No. 5138. p335-8

Adlerz,.W.C., 1972. Prodecatoma cooki, a seed chalcid on Florida grapes. J. Econ. Entomol. 63(5):1530

Cermeli, L.M. 1973. Prodecatoma cooki (Howard), (Hymenoptera:Eurytomidae), avispita de la uva (Vitis vinifera) neuva plaga de este cultivito en

Venezuela. Agronomia Tropical 23: 413-417

Cortez-Madrigal, H., J.R. Lorneli-Flores, J. Valdez-Carrazco, & I. Garcia-Ruiz. 2012. Chalcids (Hymenoptera Eurytomidae) in Vitaceae seeds of

Mexico. Southwestern Entomologist 37:361-8