Bull. Eur. Ass. Fish Pathol., 29(2) 2009, 66 Massive fish losses in rainbow trout cultures of Louros River (N.W. Greece) after strong summer rainfall. Implication of the sycamore lace bug Corythucha ciliatα (Hemiptera: Tingidae)

G. Savvidis*1, Z. Zartaloudis2 and G. Vafeas1

1 National Agricultural Research Foundation, Veterinary Research Institute of Thessaloniki, P.O.B. 60272, P.C. 57001 Thermi-Thessaloniki, Greece; 2 National Agricultural Research Foundation, Plant Protection Institute of Thessaloniki, P.O.B. 60324, P.C. 57001 Thermi-Thessaloniki, Greece.

Abstract This study aims to investigate cases of sudden fish death in rainbow trout farms located along the Louros River (region of Ioannina Prefecture, N.W. Greece) during the summer months. All of the cases have been preceded by a downpour and appeared with common and identical characteristics concerning the symptomatology (swimming behaviour, dark coloured large spots on the fish body surface) and final result (sudden death regardless of size, age and weight). The same cases were repeated many times in units located along the riversides of Louros. After conducting in situ experiments, it has been demonstrated that the phenomena are strongly correlated with the presence of the insect Corythucha ciliatα (Hemiptera: Tingidae) (Say, 1832) (common name, sycamore lace bug), which massively affects the platanus trees (common name, plane trees) along the river during the spring and summer period. The rainwater washes the leaves of the trees, and thus, an enormous number of insects (nymphs and adults) and their secretions fall down into the running river water, which is the supplier of the rainbow trout farms located in this area.

Introduction During especially hot summers (from late July to September), massive fish death cases were observed in trout farms located in a row along the Louros River in the Prefecture of Ioannina (N.W. Greece) (Figure 1). The latest massive incident took place on the 10th of August 2006, whereas the most recent case was on the 30th of August 2008. All the cases were observed after a driving rain, and they were characterised by the same symptoms (leisurely swimming, dark-coloured irregular regions on the surface of the fish body). In addition, they Figure 1. Geographical area of occurred incidents had the same final result (sudden massive fish (arrow, 39o41’ N 20o49’ E).

* Corresponding author`s E-mail: [email protected] Bull. Eur. Ass. Fish Pathol., 29(2) 2009, 67

Figure 2. Platanus trees along the riversides. Figure 3. Corythucha ciliata nymph(a) and adult(b). death regardless of size, age and weight), and and was related to an isolated trout farm that they were related to the same trout farms in had another source of water. Several separate that specific region. cases, which were on a lower scale of losses compared to the farms on the Louros River, The same cases were observed for the first time occurred during the next few years until on 13/9/1992 at six farms along the Louros August of 2006. The common characteristic River at the Mousiotitsa village area in the of all the cases was the presence in the area southern part of the Ioannina Prefecture. A of the insect C.ciliata, which commonly affects 30 min strong rainfall occurred prior to the platanus trees. sudden fish death, and the performance of the phenomenon needed about 5 min for its In this region, the sycamore lace bug expansion to the whole fish population. More (Corythucha ciliatα Say, Hemiptera: Tingidae) mass appearance related to the same farms and attacks thousands of platanus trees along the under the same conditions occurred the next riversides during the spring and summer year in the afternoon hours of 17/8/1993. The months (Figure 2). The sycamore lace bug fish showed strange behaviour, lethargy and occurs very commonly on plane trees in disorientation, and they were concentrated Europe (as a result of accidental importation at the lower areas of the basin water. A same from N. America). This insect hibernates as incident was noted after 3 days (20/8/1993) an adult under the loose bark of its host and in the area of Delvinaki (100 km northern) becomes active in early spring as the leaves Bull. Eur. Ass. Fish Pathol., 29(2) 2009, 68

Figure. 4. Platanus tree leaves infected by the insect Corythucha ciliata, a: discoloured upper surface, b: black spots on the lower surface. begin to develop. Soon afterwards the female Our basic hypothesis of the massive fish death lays eggs on the undersides of the leaves. cases is that these massive losses have a causal The females use piercing mouthparts to suck nexus with the presence of the insect C. ciliatα, plant sap from the leaves and then insert black which attack thousands of plane trees along eggs into the leaf surface (up to 200 eggs per the riversides during the spring and summer female). The eggs hatch within a few days, months. During a driving rain, the insects and the spiny, wingless black nymphs begin (nymphs and adults) and their secretions are feeding (Figure 3a). Within 4 to 6 weeks, the washed from the leaves and drop into the nymphs pupate, and the next generation river, which is the water source of the farms. of adults emerge (this is the first generation after the winter). The adults are 3 to 6 mm Materials and methods long with lacy wings (Figure 3b). Sycamore To investigate these cases, three consecutive in lace bug adults and nymphs live on the lower situ (at farm facilities in the region) experiments surfaces of the leaves and feed on leaf sap, were conducted. During the first experiment, causing yellow and white stippling on the which was performed on the 14th of August upper leaf surface (Figure 4a). As populations 2006, two metallic containers (2m x 0.5m of adults and nymphs build up, the combined x 0.25 m, 150 L) were used as experimental effect of their feeding is white spots on the tanks. In each container, there were ten trout upper surface of the leaves (and eventually (weight, approx. 100g) from the farm’s basin. yellowing or bronzing of the whole leaf). As In the first container, platanus leaves infected the insects feed, they deposit brown varnish- with C. ciliatα were washed for 1 min. The like excrement, referred to as tar spots, on the insects and their secretions, as well as the underside of the leaves (Figure 4b). Halbert leaves’ trichome (bloom of the leaves), were and Meeker (1998) stated that, in cases of released into the water in this way. The second severe infestations, the trees may be defoliated container was used as a control (water and by late summer. fish only). It should be noted that the water temperature, Ο2 and pH were measured Bull. Eur. Ass. Fish Pathol., 29(2) 2009, 69 during the experimental time. Results and discussion In the first experiment, after approximately 20 A second experiment, conducted on the min, a slight differentiation in fish activity and 27th of August 2006 at the same trout farm, reflections was noticed. The situation seemed investigated the role of the platanus leaves’ to be generalised after about 35 min. The fish trichome in this incident. In the second in the control container were reacting at once experiment, three metallic containers, like and had normal group behaviour; meanwhile, those of the first experiment, were used. in the treated container, the fish did not In each one, ten trout of the same size and react at all and seemed to have swimming weight (approx.100g) were placed in 150 L of balance problems. After 70 min., the first fish river water. In the first container, leaves from appeared with its abdomen facing up (Figure healthy platanus trees, i.e., without insects, 5a), and after 1 min, it reacted and amazingly from Central Macedonia (far away from the recovered. Afterwards, the same fish appeared region) were washed. This dip released just the nervous, with irregular movements between leaves’ trichome. In the second container, the oblique positions or vertical assaults with leaves were not dipped; instead, the material an upward direction. Dark-coloured spots collected from the leaves after careful shaking appeared on the dorsal area (Figure 5b) of two (insects and a small quantity of the bloom) of fish after 80 min., and the whole phenomenon, several infected platanus trees in the region as far as the clinical and external macroscopic was added. The third container was used as appearance, generalized after a total of 1h and the control (fish and water only). 30min. After the last occurrence, two of the fish were transported into the control container. A third experiment was performed on the 31th These fish did not recover. The opposite was of August 2006 in another nearby farm. Two also performed (transferring healthy fish metallic containers (2m x 0.65m x 0.10m) were into the problematic aquatic environment), used, into which eight fish of the same size and and those transferred healthy fish repeated weight (approx.100g) and 100 L of river water the same reaction as the fish originally in the were placed. In the first container, infected contaminated environment. After a total of 2h, platanus leaves were dipped (for 1 min), while the whole population of fish in the container the second was used as the control (fish and that had leaves of the platanus trees with water only). insects died; in addition, the fish in the control container were fine. Toxicity to the fish was considered as indicated by signs ranging from an alteration of natatory During the second experiment, in the container movements to death. with only insects, fish with unregulated movements were observed after 5 min. After As noted above, temperature, oxygen and 1h and 30min, the first fish were observed pH were regularly measured during the with the appearance of the well-known, dark- experiments. coloured areas on the surface of the body. The fish, swimming indolently without escaping Bull. Eur. Ass. Fish Pathol., 29(2) 2009, 70

1h, the first fish died. After 1h and 30 min, all the fish had died with the same external appearance (dark patches on the body surface). In addition, the recovery of the fish in the polluted container was not possible, as evidenced by their death even after transportation into the control container.

The first conclusion from the three in situ Figure 5a. Natatory problems in experimentally affected fish. experiments, in combination with the conditions, the fish appearances and the movement characteristics of the real incidents, confirms that the deaths of the fish are directly linked with the presence of the insect C. ciliata. The fact that no fish deaths occurred in the container where healthy platanus tree leaves were dipped, assures us that they are not connected to the causal agent of the phenomenon. At the locations where the cases originally appeared, strong rainfalls were b noted all year, but the fish death incidents were not observed over any periods of time except July, August and September, after the Figure 5b. Dark coloured irregular spots (arrow) on the dorsal area of the fish. platanus trees of the area developed their rich leaves and were heavily infested with from their confinement, crashed into the the insects. The insect has two generations, vertical walls of the container. After a total and the individuals of the second generation of 3h from the beginning of the experiment, follow the first adult generation at the all the fish died, except those of the control beginning of August. The maximal density container and those in the container in which of C. ciliata of the second generation is higher healthy platanus tree leaves from Central than that of the first generation (Oszi et.al., Macedonia were used. 2005). In early spring, the wintered population develops slowly because the environmental Thirty minutes into the third experiment, in circumstances are not favourable, even for the container with the leaves with insects, the the first generation. Thus, the insect mortality population had not reacted physiologically by is quite high. The mortality of the second performing indolent movements; meanwhile, generation is minimal, and since the imagoes in the control container, all the fish were can fly, there is a migration to be also taken into normal. After 45-50 min, three fish appeared account (Oszi et.al., 2005). This is supported with indolent oblique swimming, while after by the fact that, on warm September days, the Bull. Eur. Ass. Fish Pathol., 29(2) 2009, 71 air around the trees is full of flying C. ciliata patches could be scientifically interrelated. It adults. Their expansion on the tree is due to is the autonomous nervous system of fish that the mobile imagoes that tend to occupy the controls and affects the melanin diffusion in leaves uniformly. the fish skin’s chromatic cells. Because of the above mentioned reasons, the progressive As was already underlined, the insect restriction of the gills’ ability to receive oxygen appearance in the Greek territory was could be strongly hypothesised. The effort noticed for the first time in 1988. The sudden to find similar incidents in the international fish death cases were never observed in the literature had negative results, which indicates country before that year. The obvious reason how rare this phenomenon is. The existing that similar cases didn’t occurred when the references are only related to the synthesis insect was present in the country between and the study of complex chemical substances the years 1988 and 1992, is either that the (Oliver & Lusby 1988) that come from the insect had not yet arrived in this specific insect C. ciliata (excretion drops from cilia region or its population was not yet enough on the surface of the insect larvae abdomen). to cause problems. The cases have not been There are studies (Lusby & Oliver 1987, Oliver thoroughly studied previously because of the & Lusby 1988) of the repelling and paralysing standard precautionary measures of the local action of these excretions and of abilities that trout farmers, which resulted in the absence of are related to the natural procedure of the such incidents until 2006. In the case of heavy insect’s egg laying. Despite the fact that there rain, it is common practice in the region for are difficulties in its practical application, the the farmers to immediately interrupt the river direct precautionary eradication of the insect water supply during the rain and temporarily population in the platanus trees of the area is replace it with water from bores (Savvidis an environmentally dangerous solution to the et al. 2007). Drawing from the manner and problem, and it is important to point out that speed with which the incidents happened, there is a need for more detailed research on the observed clinical symptomatology, the this phenomenon. negative results of microbiological and parasitological examinations (no infectious Acknowledgements agent is able to cause relevant incidents in We would like to thank the trout farmers such a short time) and the measured normal Konstantinos Tsialios (Vouliasta, Ioannina) and physicochemical parameters of the aquatic Charilaos Manthos (Mousiotitsa, Ioannina) for environment during the experiments, it was their help by providing their farm facilities in concluded that there was the presence and which our experiments took place, and we excretion of a substance or substances with thank Dr S. Diamantis, researcher of the Forest action that were in the beginning repellent, Research Institute of Thessaloniki, for his great later paralysing and at the end murderous. The help in the first identification of the insect. damage to the nervous system of the fish was clinically obvious, and, via this observation, the quick appearance of the dark-coloured skin Bull. Eur. Ass. Fish Pathol., 29(2) 2009, 72

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Lusby WR, Oliver JE, Neal JW & Heath RR, (1987). Isolation and identification of the major component of setal exudates from Corythucha ciliatα. Journal of Natural Products 50(6), 1126- 1130.

Oliver JE & Lusby WR, (1988). Synthesis of 2-acyl-3, 6-dihydroxy-2-cyclohexen-1-ones, Tetrahedron 44(6), 1591-1596.

Oszi B, Ladanyi M & Hufnagel L, (2005). Population dynamics of the sycamore lace bug, Corythucha ciliatα (Say) (Heteroptera: Tingidae) in Hungary. Applied Ecology and Environmental Research 4(1),135-150.

Savvidis G, Zartaloudis Z & Vafeas G. Preliminary investigation of massive fish death cases in rainbow trout cultures after strong summer rainfall. Connection with the presents of Platanus tree insect Corythucha ciliata (Say,1832). Proceedings of 13th Panellenic Congress of Ichthyologists, 367-370, 27-30 September 2007, Mytilene, Greece.