Key words: Bemisia tabaci, Aphis gossypii, Liriomyza spp., Tetranychus cinnabarinus, Thrips, natural control

The studies were made in cucumber glasshouses in Menderes and Bornova of İzmir province in 1996. The population growth of Bemisia tabaci Gern, Aphis gossypii Glover, Liriomyza huidobrensis (Blanchard)), Tetranychus cinnabarinus (Boisd), Thrips tabaci (Lindeman) and Frankniella occidentalis (Pergande) were followed. The leaf miner population began to develop at the beginning of the vegetation. It was found that the %50-98 parasitism ratio was suppressed the leaf miners population density. Thrips population increased in the seedling stage and then population density decreased. It is considered that the thrips were controled by the predators. Whitefly population was increased in June-July. Aphid appeared in May-June and increased at the beginning of July. The aphid density reached the treatment threshold and damaged the plants. Although there were beneficial species they could not supressed the population density of the aphid. Spider mite was appeared at the beginning of the season, and increased in the middle of July. Spidermite also reached the treatment threshold and gave harm to the plants. The plants were faded because of the aphid and spidermite damages. Asymmetrasca decedens Paoli and Henosepilacna elaterii (Rossi) were recorded at a very low level.

The area of protected vegetable crops cultivated in Turkey is 17,865 ha. Vegetables are grown in 95 % of the glasshouses. Of this, tomato is grown in 57 %, cucumber in 27 %, pepper 8 % and others in 8 %. In the Aegean region, vegetable glasshouses occupy 19,78 ha, the production is 233,599 t.

The project was carried out to determine the population trends of the pests and their beneficials in cucumber glasshouses. The results of this project may give some clues about control methods against the major pests.

The project was conducted in cucumber glasshouses of the İzmir province in 1996. The studies were carried out in 300-100m² greenhouses of both the institute inBornova and growers plastic high tunnels in Menderes and Çamönü. The population development of whitefly (Bemisia tabaci Gern.), aphids (Aphis gossypii Glower), leafminers (Liriomyza huidobrensis (Blanchard)), spidermites (Tetranychus cinnabarinus (Boisd.)), thrips (Thrips tabaci (Lindeman) and Frankniella occidentalis (Pergande)) were followed. Twenty plants were selected randomly in the plastic tunnels. At each plant a top, middle and bottom leaf was taken and checked for the numbers of pests with a binocular in the laboratory. The larvae of the whitefly, adult and nymph of the thrips, aphid and spidermites were counted in 5 cm² and recorded. Counts were the mean of larvae or individual (adult+nimph) per cm² except leafminers which were the mean of larva per leaf. The adult populations of whitefly and leafminers were followed using yellow sticky traps (20x25 cm) positioned at a height of 15-20 cm above the plant. The adults were counted and recorded then taken from trap surface. The predator densities were counted on 50 leaves randomly chosen in the glasshouses. The larvae and adult Chrysoperla sp., the larvae of Shyrphidae, the adult and larvae of Coccinellidae, the larvae of Aphidoletes sp., the adult of Orius niger (W.), the adult and nymph of Amblyseius messor+ A. barkeri, the adult and nymph of Macrolophus caliginosus Wgn. were counted and evaluated per individual leaf. The parasitism ratios of leafminers, whitefly and aphid were found.

The whitefly species was determined to be Bemicia tabaci Gern. Whitefly was recorded at the beginning of the crop. The number of adult and larva was a maximum on June 2^nd and 8^th, respectively. When whitefly larva began to appear M. caliginosus appeared also and were found at levels of 0,6-0,8 larva/leaf in Bornova, and 0,1-0,4 individual/leaf in Çamönü throughout the season. There were no M. caliginosus in Menderes. The parasitoid (Encarsia formosa Gahan) was found only in Çamönü at 2-27 %.

The leafminer species was determined as Liriomyza huidobrensis (Blanchard). The incidence of leafminer was too low to evaluate in Bornova (1-2 adults/trap/week and 0,01-0,02 larva/leaf). The larva and adult populations were high at the beginning of the crop (in May). The adult population increased and reached maxima (4 adult/trap/week) on June 24^th in Menderes; 8260 adults/trap/week on June 17^th in Çamönü. The larva population decreased to 0,1 larvae/leaf in Menderes on June 24^th and 0,7 larvae/leaf in Çamönü on July 1^st and then the larva disappeared, the adult population decreased gradually. The parasitism ratios were between 95-98 % in Menderes and 53-96 % in Çamönü.

The thrips species were identified as Thrips tabaci (Lindeman) and Frankniella occidentalis (Pergande). Thrips were counted at 0,74 individuals/cm² in Menderes, 0,34 individuals/cm² in Çamönü, and 0,06 individuals/cm² in Bornova. Thrips density reached the maximum on June 8^th at a level of 2,4 individuals/cm² in Bornova, on June 24^th in Menderes at a level of 0,82 individuals/cm²and on July 8^th in Çamönü at a level 3,46 individuals/cm². Orius sp occured between 0,1-0,2 individuals/leaf in Menderes, 0,02-0,7 individuals/leaf in Çamönü and 0,1-0,3 individuals/leaf in Bornova. The totals of Amblyseius messor and A. barkeri were recorded at 0,1-0,5 individuals/leaf in Çamönü, 0,05-0,09 individuals/leaf in Menderes. O. niger was found in all plastic tunnels and was more abundant than Amblyseius spp.

Spidermite was present from the beginning of the crop in Bornova (0,42-26,4 individuals/cm²) and Çamönü (0,02-3,92 individuals/cm²) and appeared between June 17^th-July 1^st in Menderes. (0,02-0,08 individuals/cm²). The number of spidermites reached the maximum on June 18^th in Bornova, on June 24^th in Menderes and on July 15^th in Çamönü. The number of Chrysoperla sp. was 0.32-0.92 individuals/leaf in Menderes, 0,06-0,26 individuals/leaf in Çamönü and 1-4,3 individuals/leaf in Bornova.

Aphids appeared at the beginning of the season and reached the maximum in three greenhouses on July 15^th at 25 individuals/cm² in Menderes; 65,8 individuals/leaf in Çamönü, and 66,4 individuals/cm² in Bornova. The cucumbers withered because of the feeding of aphids, the honeydew secretion and the fumagine formation. The predators of aphid Chrysoperla sp., Aphidoletes sp and Coccinellidae (Synharmonia conglobata (L.), Adonia variegate (Gueze), Coccinella septempunctata (L.))appeared towards the end of the crop. Coccinellidae was recorded at 0.2-3.1 individuals/leaf in Menderes; 0,3-3,7 individuals/leaf in Çamönü, and 0,9-9 individuals/leaf in Bornova. Chrysoperla sp. was counted at 0,32-0,92 individuals/leaf in Menderes; 0,06-0,26 individuals/leaf in Çamönü and 1-2 individuals/leaf in Bornova. Aphidoletes sp. was found at 0,01-0,9 individuals/leaf in Menderes, 0,5-1,3 individuals/leaf in Çamönü, and 2,9-12 individuals/leaf in Bornova. Shyrphidae was found only in Bornova at a level of 0,1-0,3 individuals/leaf. The parasitised individuals also appeared late and the parasitism ratio was very low at 0,7-63 % in Menderes , 0,1-1 % in Çamönü and 0,3-10 % in Bornova.

Asymmetrasca decedens paoli was present at a low infestation level of 0,6-0,5 individuals/leaf in Menderes and 0,5-0,1 individuals/leaf in Çamönü. Henosepilacna elaterii (Rossi) was found at 0,02-0,09 individuals/leaf in May-June in Bornova.

Whitefly was established late in the spring. The larval population increased towards the end of the crop in Menderes and Çamönü, but decreased in Bornova. It is concluded that M. caliginosus was found with the increasing of whitefly larval population. It can be said that M. caliginosus can suppress whitefly population if it is established before a high larval population. The population of the whitefly larva was increasing toward the end of the crop although the population of adults was constant. In this period, the whitefly had been established recently and if the plants did not fade away because of aphid damage, the whitefly population may increase further. It was also observed that all instars of whitefly were covered with honeydew and the activity of whitefly was limited. The whitefly incidence was inhibited by the existence of aphids.

Differences could be observed in the infestation level and the population development of leafminers in the three glasshouses. The lower infestation level at the beginning of the season in Bornova may be due to the environment. Because the plastic tunnels in Bornova belong to the Institute and there are no other plastic tunnels around it. Thus, leafminers have not become established. But in Menderes and Çamönü, the population density was too low if you consider the infestation level in those localities and the infested cucumber seedlings. The trap captures indicated that adults migrated continuously from the outside. While the adult population was increasing the larval population decreased at the beginning of the crop and then disappeared. An average the parasitism ratio was 53-98 %. In this manner it could be said that the high parasitism ratio suppressed the larval population density.

Thrips population considerably in a high level of population incidences where it was infested from seedlings such as Menderes and Çamönü. In Bornova, the population level was low compared to the other plastic tunnels, because it wasn’t infested by the seedlings and there were no sources of thrips around it. The thrips population reached the highest level in the beginning of summer and then declined rapidly when O. niger appeared. In Menderes, when total population of O. nigera and Amblyseius spp. population increased the thrips population began to decrease. It was observed that thrips were also negatively affected by the honeydew of aphids. Frankniella occidentalis (Pergande) species were found on cucumber from the beginning of the season.

The infestation level of spidermites was very low at the beginning of the crop and began to increase in mid June. The infestation level of spidermite was very high in Bornova at the beginning of the crop in which the infestation level was very high in previous years. Then it decreased gradually after Coccinellidae and Chyrysopidae species were recorded in Bornova. In Çamönü and Menderes the infestation level increased gradually towards the end of the crop. It can be said that if the beneficials appeared after the spidermite population was at a high level of incidence the natural control remained weak with low incidence level of predators; severe damage occurred and the plants faded away in a short time. It was suppressed where the initial infestation level was low and the predators were established before the spidermite infestation reached a high level in Menderes. Spidermite incidence was high on the leaves which were not infested by aphids. It was observed that spidermite individuals were also affected negatively from the honeydew of aphids.

Aphids appeared at the beginning of the season and exceeded the treatment threshold (20 individuals/leaf) in June-July. In addition to this, the number of predators was too low to be effective on the aphid population. Coccinellidae was the highest in number and most common predator found over long periods among the predators. The numbers of Chrysoperla sp and Aphidoletes sp were relatively low in comparison with Coccinellidae. Shyrphidae species was the least in number and found only in Bornova. The number of predators was higher in Bornova than elsewhere. This was because sprays were not frequent in Bornova and beneficials were preserved. The parasitised individuals late appeared and the parasitism ratio was very low. In Menderes, where the parasitism ratio seems high in the first week, the aphid incidence was low in that period. Afterwards, the parasitism was decreased, while the aphid population became excessively high.

Aphid and spidermites were found to be the main pests in cucumber glasshouses. Both occured from early July, augmented rapidly and caused severe damage in spite of natural enemies. The Coccinellidae species was the main predator among Chrysopidae, Syrphidae and Aphidoletes sp. The predators couldn’t be established before aphid and spidermite were over the treatment threshold. The parasitism ratio was too low to be effective on the aphid population. Whitefly, thrips and leafminers were naturally controlled by the beneficials; M. caliginosus, O. niger and parasitoid of leafminers, respectively, in the only case that the natural balance was preserved. They will be potential pests when the frequent treatment of broad spectrum pesticides occurred. The major pest (aphid and spidermite) populations were high in the plastic tunnels which had been infested in previous years and subjected to continuous infestations from the neighbours. Thus, cultural measures should be taken for preventing the augmentation of pest populations from one season to another. The main beneficial for each pest should be studied for biological agents to support them at the high pest incidence. The natural enemies should be protected and supported in particular at the beginning of the crop. The chemicals should be selected which have the least side effects. The chemicals should be sprayed at the optimum biological stage of pests and the main natural enemies in the glasshouses.