Andricus dimorphus

Distinguished from other oak gall wasps by the clustered arrangement of galls specifically along the leaf midrib on the abaxial surface. The globular shape with pointed base and red-brown coloration, combined with formation in late summer on white oak species, separates this species from other Andricus species. Andricus pattoni, found on post oak (Quercus stellata), forms galls scattered across the leaf surface rather than clustered on the midrib. Disholcaspis species typically form twig galls rather than leaf galls.

Found in deciduous forests and woodlands where host white oak species occur. Galls develop on living oak leaves in late summer. The wasp requires mature oak trees with adequate leaf tissue for gall formation.

Central and eastern North America, throughout the range of its host oak species. Documented from Missouri and surrounding states where Quercus macrocarpa, Q. alba, Q. prinoides, and Q. bicolor occur.

Gall formation begins in late summer. Adults emerge from galls the following year; specific emergence timing not precisely documented but occurs after winter dormancy period.

Larvae feed on specialized gall tissue induced on oak leaves. Adults likely feed on nectar or honeydew, though specific adult diet not documented.

• Quercus macrocarpa - hostbur oak, confirmed host
• Quercus alba - hostwhite oak, confirmed host
• Quercus prinoides - hostdwarf chinkapin oak, confirmed host
• Quercus bicolor - hostswamp white oak, confirmed host
• Quercus muhlenbergii - hostchinquapin oak, observed host

Adult female lays egg in developing leaf tissue using ovipositor. Larva hatches and secretes plant growth hormones inducing gall formation. Larva develops inside gall, feeding on specialized tissue. Pupation occurs within gall. Adult emerges by chewing exit hole. Gall clusters readily detach from leaf when mature. Inquilines and parasitoids may inhabit galls.

Females use ovipositor to inject eggs into leaf tissue; ovipositor functions like hypodermic needle but cannot sting humans. Gall induction involves chemical manipulation of plant hormones to redirect plant growth. Galls detach readily when mature, potentially aiding in pupal development or adult emergence.

Galls provide microhabitat for inquilines and parasitoids. The wasp functions as a gall inducer that manipulates oak leaf development, creating specialized feeding structures. Role in broader ecosystem food webs not extensively documented.

No direct economic importance. Galls may cause minor aesthetic damage to ornamental oaks but are not considered significant pests. Subject of ecological and evolutionary study due to specialized plant-insect interaction.

• Andricus pattoniAlso forms leaf galls on oaks, but galls are scattered across leaf surface rather than clustered on midrib; occurs on post oak (Quercus stellata) rather than white oak species.
• Disholcaspis quercusglobulusForms round, detachable galls on oak twigs rather than leaves; single or small clusters rather than large midrib clusters.

• cynipidae
• gall-wasp
• oak-gall
• leaf-gall
• white-oak
• hymenoptera
• parasitoid-host
• inquiline-habitat

• BugGuide
• Wikipedia
• iNaturalist taxon
• Cynipidae | Beetles In The Bush
• Ted C. MacRae | Beetles In The Bush | Page 8
• Arthropoda | Beetles In The Bush | Page 7
• Gall darn it! Gall insects on hickory, oak, and elm, Phylloxera caryaecaulis, Andricus palustris, Colopha ulmicola — Bug of the Week
• Sex Attraction Pheromone Improves Detection of a Threatened Beetle
• The Insects Behind the Weird Growths on Plants