RAPID SURVEY OF DAMAGE DUE TO GALL WASP INFESTATION IN A COPPICED EUCALYPTUS CAMALDULENSIS PLANTATION IN MARAGAMUWA, NAULA IN THE MATALE DISTRICT OF SRI LANKA

According to several sources, Eucalyptus plantations in Sri Lanka are currently under threat due to an attack by a gall wasp. Our observations made at a coppiced Eucalyptus camaldulensis plantation at Maragamuwa, Naula in the Matale District revealed a heavy infestation of galls in coppiced shoots. Close examination of 40 trees in a block revealed low damage in 62.5% of the coppiced trees and heavy damage in 10% of the trees. The wasps that emerged from field collected galls were identified as Leptocybe invasa Fisher & La Salle (Hymenoptera: Eulophidae). Only female wasps emerged from the field collected galls and no parasitoids were recorded. This preliminary study highlights the severity of damage caused by L. invasa and the need to identify appropriate measures to manage this invasive gall wasp of Eucalyptus plantations in the country


INTRODUCTION
Eucalyptus was introduced to Sri Lanka as a plantation crop in the latter part of the 18 th century from Australia. Currently it is contributing to 20% of the major reforestation plantings that provide timber and fuel wood (Bandaratillake, 1993). Furthermore, Eucalyptus plantations play a dominant role in soil conservation, watershed management and provide wood and wood fiber products. Currently there are plantations of about 10 species of Eucalyptus distributed in three agroclimatic regions of the country; in the Dry and Intermediate zones and in the Up country and Low country Wet zone. Among them, Eucalyptus camaldulensis is the most widespread species planted in an area of >15,500 ha (Bandaratillake, 1993). It is one of the best known Eucalyptus species outside Australia. Economically it is the most important hardwood species of the dry lowland areas in the entire Mediterranean and Middle East regions (FAO, 1979).
Eucalyptus plantations and nurseries throughout the tropical and subtropical countries of the world are currently under threat by the gall forming invasive wasp, Leptocybe invasa (Hymenoptera: Eulophidae), commonly referred to as the blue gum chalcid (Mendel, et al, 2004;FAO, 2007). In 2000, this gall wasp was recorded from the Mediterranean region where it caused severe injury to young foliage of red river gum, Eucalyptus camaldulensis, by inducing galls mainly on rapidly growing shoots. Seedlings in nurseries, saplings in plantations and coppiced shoots in plantations are known to be more susceptible to L. invasa attack (Mendel, et al., 2004). The wasp lays eggs in the petiole and midrib of leaves and stems of young shoots that leads to gall formation. Gall formation by L. invasa damages growing shoot tips and leaves of Eucalypts, resulting in quicker abscission of leaves and drying up of shoots. Heavy galling prevents further growth of the infested shoots. Its rapid population growth and spread in countries into which Eucalyptus has been introduced is attributed to the thelotokous parthenogenetic reproduction and multivoltine development of L invasa and the absence of natural enemies (Mendel et al., 2004). L invasa is not considered a pest in Australia suggesting that the natural enemies in its native country __________________________________________ *Corresponding author's email: inokap@pdn.ac.lk keep the population level of the pest below observable level. Studies conducted in India recorded few species of naturally occurring parasitoids (natural enemies) of L. invasa. Of them, Megastigmus sp. (Torymidae) was recorded as the most abundant parasitoid of L. invasa in India .
In the plantation in Maragamuwa and Handuwa in the Naula area of the Matale District, where the study was conducted, 320 ha of land had been planted with E. camaldulensis in the late 1970's and had been coppiced in 2006/2007 to allow for natural forest recovery (Reed et al., 2009). A rapid preliminary survey was carried out in a section of this plantation to assess the severity of damage and to identify the gall forming insect.

Survey site
The rapid survey was conducted in a 4 ha block of the harvested E. camaldulensis plantation with coppiced shoots in Maragamuwa, Matale District. The site was visited on 29 th October, 2010. The surveyed block had a thick undergrowth of herbs and shrubs and the terrain was sloppy, therefore, access was not easy (Plate 1).

Assessment of the severity of damage
The 4 ha block had nearly 3500 coppiced trees of E. camaldulensis. Within a selected area in the block, 40 accessible coppiced trees were selected for the survey. The trees were located along a sloppy terrain ranging in elevation from 250-270 m. Access to each coppiced tree was made by clearing the undergrowth. The severity of damage in the coppiced growth of the selected trees due to gall formation was assessed modifying the criteria given by Thu et al, (2009)

Collection of gall forming insects from infested shoots of E. camaldulensis
Randomly selected ca. 15 small branches with mature galls were excised and brought to the Entomology Laboratory at the University of Peradeniya. The cut ends of branches were dipped in water and the branches were covered with ventilated polythene bags. Insects that emerged over a period of 25 days (by which time the braches had dried up) were collected and preserved in 70% alcohol. Wasps were identified using the descriptions given by Mendel et al. (2004) and Protasov et al. (2008).

RESULTS AND DISCUSSION
Of the coppiced E. camaldulensis trees examined, majority (62.5%) had a low infestation, with only 10% of the trees having a heavy infestation (Table 1). Galls of different stages (Plate 2) were present in 90% of the examined E. camaldulensis coppiced trees.  (Plates 3 and 4), over a period of 25 days. These were identified as Leptocybe invasa Fisher & La Salle, 2004 (Plate 5). On close examination, all the wasps that emerged were found to be females. According to studies conducted in Israel (Mendel et al., 2004) males were not found among thousands of L. invasa wasps that emerged from galls in E. camaldulensis and few other Eucalyptus species. However, Protasov et al. (2008) and Kavitha  had encountered males of L. invasa in India.
No other insect species emerged from galls of the coppiced shoots held in the laboratory, indicating the absence of natural enemies of L. invasa in the field collected sample. This may be due to the small number of shoots held in the laboratory or the low prevalence or absence of natural enemies at the site. In India, Gupta and Poorani (2009)  (Mymaridae) and Telenomus sp. (Scelionidae). Of these, Megastigmus sp. was the most abundant. Native Megastigmus species are known to parasitize L. invasa in Italy, Turkey and Israel (Viggiani et al., 2000;Protasov et al., 2008).
According to personal information of Dr. N.D. R. Weerawardane (Forest Research Centre, Kumbalpola, Sri Lanka), damage due to gall formation in Eucalyptus has been seen over several years. Recent observation by scientists at the Tea Research Institute, Sri Lanka has indicated gall wasp infestations in E. grandis, E. robusta and E. microcorys as well. In the world, 13 species of Eucalyptus (E. botryoides, E. bridgesiana, E. camaldulensis, E. deanei, E. globulus, E. gunii, E. grandis, E. saligna, E. maidenii, E. nitens, E. robusta, E. tereticornis and E. viminalis) have been identified as susceptible to L. invasa (Thu et al, 2009;Mendel. et al., 2004;FAO-Health and Biosecurity working papers, Kenya, 2007). Of them, only five Eucalyptus species are present in Sri Lanka. Based on the extent and distribution of Eucalyptus plantations in the country, 97% of the plantations could be under threat by L. invasa. Eucalyptu camaldulensis represents 55% of the Eucalyptus plantations in the country that are largely confined to the Dry and Intermediate zones. According to Mendel et al. (2004), the gall wasp prefers warmer climates. In Israel, oviposition by adult wasps and all development stages of the wasp were observed during warmer climates. Their development was slow and suppressed during winter seasons. In Sri Lanka, warmer climates prevailing throughout the year in Dry and Intermediate zones may provide optimum conditions for the gall wasp development in its most preferred host, E. camaldulensis. Eucalyptus camaldulensis is known to be one of the most susceptible hosts of L. invasa (Krishnakumar and Jacob, 2010;Thu, et al., 2009;Branco et al., 2005 andMendel et al., 2004).
This study highlights the threat to Eucalyptus plantations in general due to L. invasa and particularly to E. camaldulensis. Research in wider spatial and temporal scales to determine the impact of the gall wasp on Eucalyptus plantations in Sri Lanka and management strategies including biological control need to be addressed urgently.