Field Trials Measuring the Effects of Ultraviolet-Absorbing Greenhouse Plastic Films on Insect Populations

Abstract

Field studies were conducted to compare insect population levels in greenhouse crops covered with plastics that block the transmission of UV light in two wavelength ranges. Crops grown in greenhouses under a plastic that blocked UV light at wavelengths of 380 nm and below had lower numbers of aphids and thrips compared with a plastic that blocked UV light at wavelengths of 360 nm and below. This is consistent with the results found for thrips in previous studies using small, completely enclosed tunnels with no plant material. The effects were not as dramatic in the commercial greenhouses, perhaps due to unfiltered light entering through the open sides of those greenhouses. There was no reduction in greenhouse whitefly, Trialeurodes vaporariorum Westwood, populations under the <380 UV-absorbing plastic compared to <360 nm UV-absorbing plastic in these field trials. This is inconsistent with results found in small, completely enclosed tunnels, where sticky traps caught a significantly higher proportion (95 +/- 2%) of released greenhouse whiteflies inside tunnels covered with <360 nm absorbing plastic compared with the <380 nm absorbing plastic. The results of these studies suggest that the type of greenhouse plastic used in a structure can affect population levels of some insect species, and may be useful tools in developing integrated pest management programs for insect management. The design of the greenhouse and amount of unfiltered light that enters the system appear to be important factors in determining the level of effect.

Bumblebee search time without ultraviolet light

“…This is probably because when UV-coverings are used the UV+ vents make a higher colour contrast and the bees may exhibit positive phototaxic behavior towards the UV+ (Morandin et al, 2002). There is some evidence to suggest that in UV+ environments bees are more active (Costa and Robb, 1999;Morandin et al, 2001b;Costa et al, 2002), although this was not found in the Morandin et al (2002) study. The possibility that bees might not forage as efficiently in UVenvironments (Morandin et al, 2001b) is likely to be because bees are attracted to any UV+ conditions, so in large greenhouses with UV-coverings bees seek out any UV+ illumination sources (such as vents).…”

“…For example, Morandin et al (2001b) found that in commercial greenhouses fitted with ultraviolet-transmitting plastic the mean activity of individual bumblebees Bombus impatiens was 4.82±0.37 trips per day, whilst in commercial greenhouses that excluded ultraviolet radiation the activity averaged 2.37±0.37 trips per day. Increased activity in greenhouse environments that transmit more ultraviolet radiation has also been reported for several other species of insects (Antignus et al, 1996;Costa and Robb, 1999;Costa et al, 2002). However, in a study using miniature greenhouses in a tightly controlled environment Morandin et al (2002) did not find that bumblebees were more active under high UV-transmitting coverings.…”

“…Several studies have observed that insects appear to be less active when greenhouses are covered with a material that reduces the transmission of ultraviolet radiation relative to other wavebands of visible light (Antignus et al, 1996;Morandin et al, 2001b;Costa and Robb, 1999;Costa et al, 2002). Fig.·2 shows that bumblebees perceive a change in colour when the ultraviolet content of the illumination source is altered.…”

Insect reactions to light and its applications to pest management

“…For insects given access to a space with UV radiation and a space from which near-UV radiation was eliminated, many species avoid the latter. Studies have shown reduced incidence of insects such as aphids, whiteflies, and thrips in facilities covered with UVabsorbing film (Costa et al 2002;Nguyen et al 2009;Nonaka and Nagai 1985;Ohta and Kitamura 2006). In addition to vinyl chloride films, products made of highly durable polyolefin films have recently been developed to block near-UV radiation, to prevent infestation inside greenhouses.…”

Seasonal climatic variations influence the efficacy of predatory mites used for control of western flower thrips in greenhouse ornamental crops

“…It is presumed that pest infestation levels may be associated with exposure to different UV wavelengths, and WFT have been shown to be attracted to UV light (Costa et al, 2002). Lower numbers of aphids and thrips were recovered on crops in greenhouses that blocked UV light at 380nm than those that blocked UV of 360nm and below (Costa et al, 2002). …”