Disholcaspis quercusvirens
Bullet galls were initiated by the sexual generation of D. quercusvirens during early shoot expansion in the spring. Slight stem swellings were visible by June, and small red-colored bullet galls with soft and spongy tissue (Fig. 1A) emerged through the bark by August. A sweet and sticky exudate occurred on the bullet galls from August to mid-October, when only larvae were present inside the galls. This exudate attracted red imported fire ants (Solenopsis invicta Buren), velvet ants (Hymenoptera: Mutillidae) (Fig. 1B), and paper wasps (Hymenoptera: Vespidae), and supported sooty mold growth (Fig. 1C). D. quercusvirens bullet galls were mature and woody (Fig. 1D) in the fall, reaching their maximum diameter by November (Fig. 2).
Mean maximum bullet gall diameter was 7.7 ± 0.1 mm in 2007 and 4.8 ± 0.1 mm in 2008 on the trees at the nursery (Fig. 2). Compound galls were 30.4 ± 1.6 mm in length with 9.3 ± 0.6 bullet galls per compound gall (range: 1–44 bullet galls) in 2007 and 25.5 ± 1.4 mm in length with 11.0 ± 0.9 bullet galls per compound gall (range: 1–52 bullet galls) in 2008.
Asexual females (Fig. 3A) emerged during cold weather periods from late-November through January and oviposited into dormant buds (1.3 ± 0.07 mm in length, 1.2 ± 0.09 mm in width at base). Females (n = 20) carried 64.0 ± 3.0 eggs (range: 43–88 eggs). All eggs within female abdomens appeared to be of similar size, but dimensions were not measured.
In total, 1,650 bullet galls were collected from 1 August to 18 December 2007, and 91.3% were parasitized (Table 1). The natural enemy complex included species of Synergus (Cynipidae), Eupelmus (Eupelmidae), Eurytoma and Sycophila (Eurytomidae), Ormyrus (Ormyridae), and Acaenacis (Pteromalidae) (Fig. 4).
Bullet gall height, diameter, and number of bullet galls per compound stem gall were influenced by the gall inhabitant. Bullet galls containing D. quercusvirens and parasitoids in 2007 were significantly wider than those containing inquilines. Bullet galls with live D. quercusvirens were significantly taller than those containing parasitoids or inquilines. Furthermore, compound galls with more than five bullet galls in a cluster produced more D. quercusvirens than compound galls having five or fewer bullet galls.
Bullet galls from which gall makers successfully emerged did not produce any parasitoids or inquilines. However, two or more parasitoids and/or inquilines emerged from many D. quercusvirens bullet galls and presumably killed or out-competed the gall maker. Although inquilines are phytophagous, their development may cause gall maker death because of overcrowding or competition.
