Integrated Protection of Olive Crops IOBC/wprs Bulletin Vol. 59, 21 pp. 171-176 Current status of Saissetia oleae biological control in Sardinia (Italy) Gavino Delrio, Cipriano Foxi Dipartimento di Protezione delle Piante, Università di Sassari, Via E. De Nicola, 71 Sassari E-mail: gdelrio@uniss.it Abstract: During 1993 and 28 the parasitoid complex of black scale, Saissetia oleae (Oliv.), was studied in olive groves of Sardinia after the encyrtids Metaphycus helvolus (Comp.) and M. lounsburyi (How.) were introduced in the period 1981-1982. The parasitism rate on nymphs was 6.7% in 1981, before the introduction of the two encyrtids, and 8.% and 5.3% in 1993 and 28, whereas the parasitism rate on females was 21.%, 23.7% and 7.7%, respectively. The pteromalids S. caerulea (Fonsc.) and Moranila californica (How.) were the dominant parasitoid species in 1981, whereas the introduced M. helvolus and M. lounsburyi were the most abundant species in 1993. M. helvolus and M. lounsburyi, introduced for the first time 3 years ago, are well established and provide biological control of black scale in combination with other natural enemies. Key words: Saissetia oleae, parasitoids, biological control, Sardinia Introduction The black scale, Saissetia oleae (Oliv.), is the most widespread and frequent scale insect on Mediterranean olive trees. Its abundant honeydew favours the development of sooty mould fungi, that can reduce photosynthesis and respiration in the leaves which drop prematurely. Under heavy infestations, olive production may even be annihilated for a number of years (Katsoyannos, 1992) Saissetia populations often exhibit considerable abundance fluctuation within the same year and between different years because of biotic and abiotic factors, such as the action of natural enemies, the use of pesticides, and harsh environmental conditions such as extreme temperatures. Until the 198s, the complex of entomophagous species active on S. oleae in Sardinia was comprised mostly of predators, the coccinellids Exochomus quadripustulatus (L.), Chilocorus bipustulatus (L.) and Lindorus lophantae (Blaisd.) and the lacewing Chrysoperla carnea (Steph.) and some parasitoids, such as the aphelinid Coccophagus lycimnia (Walk.) on 2 nd and 3 rd instar scales and the pteromalid Scutellista caerulea (Fonsc.) on ovipositing black scales (Delrio, 1983). The most important additions to the parasite complex of S. oleae were the encyrtid Metaphycus hageni Daane & Caltagirone (previously reported as M. lounsburyi (How.), Guerrieri & Noyes, 2) that attacks mainly 3 rd instar and young females and the pteromalid Moranila californica (How.) that develops as an egg-predator. These parasitoids spread to many sites in Sardinia (mostly along the coastal zones) (Delrio, 1983) after their accidental introduction in the Mediterranean basin around the 197s (Viggiani, 1978). In 1979-1982 two other parasitoids, the encyrtids Metaphycus helvolus (Comp.) and M. lounsburyi (How.) (= M. bartletti Ann. et Mynh.) were introduced on purpose in Sardinia to increase the biological control of the black scale. M. helvolus is a solitary endoparasitoid of 171
172 several soft scale species that attacks 2 nd and early 3 rd instar black scale nymphs. This parasitoid, that originated in South Africa, has been mass reared since 1937 in California and was introduced in Greece in 1962 (Argyriou & DeBach, 1968). M. lounsburyi, introduced in Israel from South Africa during 1976-1978 (Argov & Rossler, 1993), is a gregarious endoparasitoid that develops on 3 rd instar nymphs, non-ovipositing and ovipositing females. The purpose of this report is to present an account on the current status of the black scale biological control in Sardinia after the introduction of the two latter parasitoid species. Material and methods M. helvolus and M. lounsburyi were imported to Sardinia from the Institute of Subtropical Plants and Olive Tree of Chania (Greece) and the Station de Zoologie et de Lutte Biologique of Antibes (France). Parasitoid colonies were maintained in the laboratory of the University of Sassari, on black scale reared on 2- to 3-yr old oleander bushes. From 1981 to 1982, about 25 M. helvolus adults and about 23 M. lounsburyi adults were released in infested olive groves in northwestern Sardinia (Sorso, Sassari province). Releases were performed mostly when the proper black scale host stages were most frequent. Black scale phenology, parasitoid incidence and flight period of parasitoids were studied in the same olive groves where the releases were made. To determine the age structure of black scale, one hundred 2cm long twigs were collected each week during 1981 from 5 olive trees. The total number of olive scales were counted in laboratory using a stereomicroscope and categorized as one of the three immature stages or as pre-ovipositing or ovipositing female. The incidence of parasitoid complex on black scale was studied during 1981, before M. helvolus and M. lounsburyi introduction, and after their releases in 1993 and 28 sampling infested twigs with leaves at irregular time intervals. Leaves and twig pieces with black scale nymphs or females were placed in different ventilated transparent plastic cages in laboratory at 25 degrees for one month and the emerging adult parasitoids were counted and identified. The flight period of parasitoids was determined from April to October 1993 counting under a stereomicroscope the number of adult parasitoids captured by 1 yellow sticky traps that were hung at a height of 2 m on the canopy of olive trees and replaced weekly. Results and discussion On olive trees in northwestern Sardinia the black scale has one generation per year and a partial second generation. Overwintering is ensured mainly by 2 nd and 3 rd instar nymphs whereas the egg laying period is concentrated in May-June and the crawler emergence peaks in July. A partial second generation occurs in autumn, but apparently it is not important to the overall population density (Figure 1). During our study in 1981, before the releases of M. helvolus and M. lounsburyi, 612 parasitoid adults were obtained from 6,318 sampled scales (Table 1). The rate of parasitism on 2 nd and 3 rd instars was 6.7% mainly due to C. lycimnia while M. flavus was rare. The ovipositing black scale females were parasitized by S. caerulea and M. californica at a total percentage of 21.%.
173 1 5 Ovipositing females 1 5 Immature females Developmental stages of S. oleae Percentage 1 5 1 2nd instar 3rd instar 5 1 5 1st instar J F M N D Figure 1. Relative abundance of Saissetia oleae developmental stages on olive trees in North Sardinia (Sorso, Sassari province, 1981). During 1993, 1 years after the introduction of the two parasitoid species, a total of 1,713 parasitoid adults emerged from 5,89 scales (Table 1). The percentage of parasitism observed was 8.% on 2 nd and 3 rd instar nymphs and 23.78% on females. The main parasitoids on nymphs were the introduced encyrtids M. helvolus and M. lounsburyi, whereas the activity of the native C. lycimnia and M. flavus was very low. From immature and ovipositing black scale females we mostly obtained M. lounsburyi and M. hageni that predominated on S. caerulea. No adults of M. californica emerged from ovipositing black scale females in 1993, in spite of their abundance in 1981. In 28, 267 parasitoid adults were recorded from 2,956 black scales sampled. The estimated rate of parasitism was 5.3% and 7.7% on nymphs and females, respectively. The parasitoid species recovered were the same detected in 1993. The most abundant parasitoid was S. caerulea followed by M. lounsburyi and M. hageni.
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175 The adult parasitoids captured at the yellow traps confirmed the seasonal trend observed in the emergence cages (Figure 2). C. lycimnia was captured in the olive grove from April to October with a peak in May, when the maximum density of 3 rd instar black scale was recorded. M. helvolus showed three peaks in May, July and September. Adults of M. lounsburyi, that develop mainly on young females, were captured from May to September with a peak in August. The oophagous pteromalid S. caerulea was present from July to October and the captures of adults showed 3 peaks, probably corresponding to 3 generations on ovipositing black scale females. 2 Coccophagus lycimnia 15 1 5 8 Metaphycus lounsburyi 6 4 2 5 4 Metaphycus helvolus 3 2 1 8 Scutellista caerulea 6 4 2 Figure 2. Seasonal abundance of the main parasitoids of Saissetia oleae captured by yellow traps in North Sardinia (Sorso, Sassari province, 1993). M. helvolus and M. lounsburyi, introduced for the first time 3 years ago, are well established and provide biological control of black scale in combination with other natural enemies. M. lounsburyi may be considered the most important and widespread black scale parasitoid in Sardinia. Despite the establishment of a fair complex of parasitoids, the black scale remains an occasional pest on olive groves in northwestern Sardinia. The different parasitoid activity observed over the years could be related to the influence of climatic factors that affect parasitoid survival or effectiveness, to the side effects of insecticidal treatments against the olive fruit fly or to an inadequate host synchronization in some years. References Argov, Y., Rossler, Y. 1993: Biological control of the Mediterranean black scale, Saissetia oleae (Hom.: Coccidae) in Israel.- Entomophaga 38(81): 89-1. Argyriou, L. C., DeBach, P. 1968: The establishment of Metaphycus helvolus (Compere) (Hym. Encyrtidae) on Saissetia oleae (Bern.) (Hom. Coccidae) in olive groves in Greece. Entomophaga 13(3): 223-228.
176 Delrio, G. 1983: The entomophagous insects of Saissetia oleae (Oliv.) in Sardinia. In: Proceedings of the E. C. Experts Meeting Entomophages and biological methods in integrated control in olive orchards, Chania, Greece, 11-12 March 1982: 15-23. Guerrieri, E., Noyes, J. S. 2: Revision of European species of genus Metaphycus Mercet (Hymenoptera: Chalcidoidea: Encyrtidae), parasitoids of scale insects (Homoptera: Coccoidea). Systematic Entomology 25: 147-222. Katsoyannos, P. 1992: Olive Pests and their Control in the Near East. FAO Plant Production and Protection, Paper 115. Mazzone, P. & Viggiani, G. 1983: Stato attuale dei parassitoidi di Saissetia oleae (Oliv.) in Italia, con notizie biologiche preliminari sui Prococcophagus varius Silv. e P. saissetiae Ann. e Myn. (Aphelinidae) di recente introduzione. Atti XIII Congr. Naz. It. Ent., Sestriere-Torino: 191-196. Viggiani, G. 1978: Acclimatato in Italia Metaphycus helvolus (Compere), parassita di Saissetia oleae (Oliv.) e di altre dannose cocciniglie. Boll. Lab. Ent. Agr. Portici 35: 25-29. Viggiani G., Mazzone, P. 198: Metaphycus bartletti Annecke & Mynhardt (1972), (Hym. Encyrtidae) parassiti di Saissetia oleae (Oliv.). Boll. Lab. Ent. Agr. Portici 34: 217-222.