Factors affecting success of galls of <i>Aditrochus coihuensis</i> (Hymenoptera: Pteromalidae)

Abstract:
Galls of Aditrochus coihuensis (Hymenoptera:
Pteromalidae) were collected from their host tree, the southern beech
Nothofagus dombeyi, near San Carlos de Bariloche, Argentina, during the
spring of 2007. Galls were carefully examined and classified as successful
or unsuccessful based on insect remains and emergence-hole diameter.
Gall properties (diameter, wall thickness, chamber diameter, wall
toughness) were measured and compared between successful galls and
unsuccessful (parasitized) galls. Gall diameter and wall thickness were
strongly correlated and thick walls seem to function as a protection against
parasitoids. Parasitoids (Torymidae) that were found within some galls had
an ovipositor length shorter than wall thickness of fully developed galls.
Most likely, parasitoids attack galls only during a limited time when the wall
338 Rev. Soc. Entomol. Argent. 70 (3-4): 337-34, 2011
is thin enough. Wall toughness did not seem to influence gall success. In
total 67% of the galls suffered from parasitoids. Inquilines (Curculionidae)
were found within some gall walls, with preference for larger galls and for
those with thicker walls. Traces of potential bird or wasp predation were
also found in a few specimens. Our present findings contribute original
descriptive information on these galls. Overall, our results lend further
support on the potential importance of natural enemies on gall evolution.

Abstract in Spanish

Agallas provocadas por Aditrochus coihuensis

(Hymenoptera: Pteromalidae) sobre su hospedero, Nothofagus dombeyi,

fueron colectadas en la vecindad de San Carlos de Bariloche, Argentina,

durante la primavera de 2007. Las mismas fueron examinadas y clasifi cadas

como exitosas o no, sobre la base de restos de insectos dentro de ellas y

el diámetro del agujero de emergencia. Distintas propiedades de las

agallas (diámetro, grosor y dureza de la pared y diámetro de la cámara)

fueron medidas y comparadas como exitosas y no exitosas (parasitadas).

El diámetro de las agallas tuvo una fuerte correlación con el grosor de la

pared, variable que se asocia con la protección contra los parasitoides.

Los parasitoides (Torymidae), que fueron hallados dentro de las agallas,

poseen un ovipositor más corto que el grosor de las paredes en aquellas

plenamente desarrolladas. Sin embargo, es posible que los parasitoides

ataquen las agallas por una ventana temporal, cuando las paredes son aún

delgadas. La dureza de las mismas, por su parte, no infl uyó sobre el éxito de

las agallas. También, se hallaron inquilinos (Curculionidae) dentro de ellas,

en mayor frecuencia en las de mayor tamaño y con paredes más gruesas.

Finalmente, se observaron evidencias de depredación, posiblemente por

aves o avispas.