Note on gynandromorphism in the eucalyptus defoliator Thyrinteina arnobia ( Stoll , 1782 ) ( Lepidoptera : Geometridae )

The brown moth Thyrinteina arnobia (Stoll, 1872) (Lepidoptera: Geometridae) is an important pest in Brazilian eucalyptus plantations. A gynandromorph individual of T. arnobia was found in a population of this pest in a laboratory rearing and it is described.

The occurrence of gynandromorphism in Lepidoptera is rare.Its frequency in some species is about 0.000125%, i.e., there is a gynandromorphy for every 8000 normal individuals (Josephrajkumar et al. 1998).The gynandromorphs may arise during the development of a male zygote (XX) with loss of an X chromosome or due to the fertilization of an egg with two female nuclei (Robinson 1971).Other organisms may induce gynandromorphs by infection of Wolbacchia bacteria causing female pattern in individuals genetically males (Pereira et al. 2003).
Lepidoptera gynandromorphs are more easily recognized when males and females are sexually dimorphic.The gynandromorphism is usually expressed bilaterally -an abnormal adult has half of the body typical of male and the other half typical of female (Josephrajkumar et al. 1998).On the other hand, this distinction may not be obvious in individuals with mosaic gynandromorphism, because male tissues are mixed with those of females, and in this case abnormalities are often determined only by analyses of the internal organs of these organisms.
The brown moth Thyrinteina arnobia (Stoll, 1782) (Lepidoptera: Geometridae) is an important pest causing signifi cant losses in the eucalyptus crops in Brazil.This has led to a number of studies with T. arnobia including its biological control (Zanuncio et al. 1994).A gynandromorph of this species reared in laboratory conditions is herein reported and described for the fi rst time.
Individuals of T. arnobia were maintained in the laboratory of Biological Control of Insects, of the " Instituto de Biotecnologia Aplicada a Agropecuária (BIO-AGRO)" at the Federal University of Viçosa, city of Viçosa, State of Minas Gerais, Brazil for two generations.Caterpillars were reared in Eucalyptus plants or in plastic vials (500 ml) containing fresh leaves of the host plant.The eucalyptus leaves were changed daily.Newly emerged adults were put in cages to obtain egg masses to maintain a stabilized population of T. arnobia in laboratory conditions as well to support experiments of biological control.
Thyrinteina arnobia is sexually dimorphic: females have longer wingspan, fi liform antennae and light coloration (Figure 1) while males have smaller wingspan, pectinated antennae and brown to black color (Figure 2).The gynandromorphy of T. arnobia was found during normal procedures of removing adults from the plastic vials to the reproduction cage.This individual is a bilateral gynandromorph with male characters such as brown wings, large eyes, pectinated antennae and short wingspan on the left side, and longer wingspan, light wings, fi liform antennae and smaller eyes on the other side (Figure 3), typical of female phenotype.
The reproductive system of the gynandromorph of

Fig. 1 -
Fig. 1 -The normal Thyrinteina arnobia female.Note wing coloration and fi liform antennae.Scale bar = 0.5 cm.Fig. 2 -The normal Thyrinteina arnobia male.Note wing coloration and pectinated antennae.Scale bar = 0.5 cm.Fig. 3 -The Thyrinteina arnobia gynandromorph.Note the male characters (brown wings, larger eyes and pectinated antenna) on the left side and female characters (clear wings, fi liform antenna and smaller eyes) on the right side.Scale bar = 0.1 cm.