HORTSCIENCE 41(3):711–716. 2006. UV-absorbing films are effective in reduc- ing insect transmitted viral diseases (Antignus et al., 1996). A significant reduction in virus Impact of Ultraviolet-blocking Plastic spread has been observed in Bemisia-transmit- ted viruses such as tomato yellow leaf curl virus Films on Insect Vectors of Virus (TYLCV) and cucurbit yellow stunting disor- der virus (CYSDV) in tomato and cucumber Diseases Infesting Crisp Lettuce crops, respectively (Antignus, 2000). This significant decrease in the spread Beatriz M. Díaz of these viruses has been attributed to the Departamento de Protección Vegetal, Instituto de Ciencias Agrarias, Centro de impairment of whiteflies to fly and disperse Ciencias Medioambientales-CSIC, C/Serrano 115 dpdo., Madrid 28006, Spain in the absence of UV-light (Antignus, 2000; Antignus et al., 2001). Ricardo Biurrún Most of the information related to the effects Instituto Técnico de Gestión Agrícola, S.A. Ctra. El Sadar s/n, Edifi cio El of UV-light absorbing plastic films on insect populations and virus spread has concentrated Sario, Pamplona 31006, Spain in tomato and cucurbits. To our knowledge, Aránzazu Moreno, Miguel Nebreda, and Alberto Fereres1 there is no information on the impact of UV- absorbing plastics on insect pests and virus Departamento de Protección Vegetal, Instituto de Ciencias Agrarias, Centro de diseases commonly found in lettuce crops Ciencias Medioambientales-CSIC, C/Serrano 115 dpdo., Madrid 28006, Spain grown under greenhouse environments. Additional index words. Lactuca sativa, UV-blocking film, photoselective barrier, aphids, The aim of this work was to study the population dynamics of insect pests and the thrips, whiteflies, virus spread of insect-transmitted viruses in a let- Abstract. Ultraviolet (UV)-absorbing plastic films are being used as a photoselective barrier tuce crop grown in a greenhouse covered by to control insect vectors and associated virus diseases in different horticultural crops. A a UV-light absorbing film. Also, the impact of 2-year experiment was carried out in northeastern Spain (Navarra) to evaluate the im- UV-absorbing films on the growth and yield of pact of a UV-blocking film (AD-IR AV) on the population density of insect pests and the lettuce as well as the mean temperature inside spread of insect-transmitted virus diseases associated with head lettuce [Lactuca sativa the greenhouse was compared to that obtained (L.)]. Results showed that the UV-absorbing plastic film did not loose its ability to filter UV when using standard polyethylene films. radiation after three lettuce crop cycles (14 months). The UV-absorbing plastic film was effective in reducing the abundance and in delaying the colonization of lettuce by aphids Materials and Methods [Macrosiphum euphorbiae(Thomas) and Acyrthosiphum lactucae(Passerini)]. A significant increase in the percentage of marketable plants was achieved under UV-absorbing films Experimental design. The experiments were due to a reduction in the number of plants infested by aphids and by insect-transmitted conducted on a crisphead lettuce crop grown virus diseases (mainly potyviruses). Also the UV-absorbing plastic films were effective in under greenhouse conditions at Sartaguda reducing the population density of Frankliniella occidentalis (Pergande) and the spread (latitude 42º21'N, longitude 1º38'W, altitude of tomato spotted wilt virus (TSWV) as well as the population density of the lepidopteran 310 m), Navarra (Spain), and were replicated pest, Autographa gamma (L.), a common pest of lettuce in Spain. However, no effective three times: Fall 2002, Spring 2003, and Fall control of the greenhouse whitefly Trialeurodes vaporariorum (Westwood) was achieved. 2003. Two commercial greenhouses, walk-in The results showed that UV-absorbing plastic films are a very promising tool to protect tunnel type, measuring 40 m long × 9 m wide greenhouse lettuce from the main pests and insect-transmitted virus diseases occurring × 2 m high were used to compare the two types in northeastern Spain. of plastic film covers. Both greenhouses were separated with 50 m between each other, had the Lettuce [Lactuca sativa (L.)] grown under biopesticides (Costa et al., 2001) and natural same orientation and were identical except for protected environments is very susceptible to enemies (Chyzik et al., 2003). the type of plastic film cover to be tested. heavy infestations of insect pests and conse- The UV-blocking films act as a photose- Each greenhouse had unscreened small quently to the spread of insect-transmitted virus lective barrier that modifies the greenhouse openings at each side of the tunnel and on the diseases. This threat has adverse ecological environment and disrupts the normal insect roof to facilitate ventilation. These openings consequences because of the large amount behavior so as to discourage pest activity. As a allowed unfiltered light to enter the greenhouse of pesticides that are currently being used to consequence few insects invade these structures structure. Doors were occasionally covered protect lettuce from insect pests. Also, pesticide and the opportunity for virus transmission is with nets to avoid wind damage to lettuce residues are a major concern to consumers be- reduced (Raviv and Antignus, 2004). Although plants. A black plastic mulch covering the soil cause lettuce is consumed as a fresh vegetable most of the plastic films contain UV-absorbing was used for weed control and to increase soil without any kind of processing. properties to extend the life of the material, temperature. Air temperature was recorded Among insect control methods, physical only a few plastics are available on the market continuously during the whole crop growth barriers continue to play a significant support- to block over 95% of UV light transmission in cycle by a thermograph (model Standard MX ing role today and are likely to have a significant the range between 200 to 380 nm while allow- 173; Robert E. White Instruments, Boston, role in the integrated pest management (IPM) ing 80% transmission of photosynthetic active Mass.) placed in the middle of each of the programs of the future (Boiteau, 2002). The use radiation (PAR) (Antignus et al., 1996). two tunnels. of UV-blocking cladding materials can play a The blockage of UV radiation interferes Plastic fi lms tested. Two types of plastic part in IPM programs for crop protection in with insect vision, navigation, orientation and films were used for comparison: a UV-absorb- greenhouses (Antignus and Ben-Yakir, 2004) feeding behavior causing a significant reduc- ing film (AD-IR AV clear manufactured by because they are compatible with the use of tion in population density and dispersion of Ginegar Plastic Products Co., Ginegar, Israel) insect pests such as aphids, thrips and whiteflies and a non-UV absorbing film (control) standard Received for publication 30 Jan. 2005. Accepted for publication 9 Mar. 2006. We thank the Spanish (Antignus et al., 1996, 1998, 2001; Costa and polyethylene plastic film commonly used at the Ministry of Science and Technology (Research Grant, Robb, 1999; Costa et al., 2002; Mutwiwa et experimental site and called Astrolux (Hyplast no.: AGL:2000-2006 and AGL-2003-07532-C03-01 al., 2005). Chyzik et al. (2003) observed that Ltd., Hogstraten, Belgium). Both types of for funding this work. UV-absorbing films also acted as an inhibitor plastic films had similar physical properties 1To whom reprint requests should be addressed. of Myzus persicae (Schulzer) propagation and (thickness, anti-drip, anti-dust, thermicity, e-mail [email protected]. dispersal by reducing its flight activity. visible light transmission and diffusion) ex- HORTSCIENCE VOL. 41(3) JUNE 2006 711 JuneBook 711 4/4/06 11:00:38 AM cept for their ability for UV-blockage. The (e.g., Autographa gamma L.) which reached to monitor landing rates of insects potentially light transmitted for both plastic types was economically damaging levels. Insecticidal acting as virus vectors (aphids, thrips, whiteflies measured experimentally at the beginning baits [clorpirifos 1% (GB) p/p] and two Bacil- and leafhoppers). Insects were collected from and at the end of the three lettuce growing lus thuringiensis 24% (WP) p/p sprays were the traps at intervals of 15 d starting just after seasons. The amount of UV (250 to 400 nm) applied in both greenhouses to selectively plant transplant. and visible light (400 to 700 nm) transmitted control these lepidopteran pests and to avoid At the same time, 15 plants per sector were by both plastic types was measured using a any detrimental effects on insect vectors of randomly selected following a zig-zag pattern spectroradiometer (models UVM and BQM, virus diseases. No pesticides were needed in and visually inspected every 2 weeks as well respectively, Spectrum Technologies, Apogee the experiment conducted in Spring 2003. as at harvest time to determine the presence Instruments, Logan, Utah). Measurements Insect sampling methods. Each greenhouse or absence of insect pests colonizing lettuce were taken inside and outside the plastic tun- was divided for statistical purposes into four- plants. For aphids, a density scale was used to nels by placing the sensor perpendicularly to sectors or quadrants (replications) of equal size indicate the level of aphid infestation on the open sunlight in a sunny day at 12:00 HR with during the experiment of 2002 and six sectors inspected plants, as follows: 0 = no aphids, <5 an outside air temperature of 15 °C. (replications) of equal size during the two = plants infested with 1 to 4 aphids and >5= Cropping practices. The impact of the experiments of 2003 for sampling purposes. plants infested with 5 or more aphids. This UV-blocking film (AD-IR AV) on insect pests Insect population dynamics were monitored in scale was used because 5 aphids/plant is the and diseases was evaluated on three lettuce- three different ways: sticky traps, horizontal threshold value established for acceptance or growing cycles in two different seasons, Fall water traps and visual counting.