Window traps and direct observations record similar arthropod flower visitor assemblages in two mass flowering crops

Abstract

Understanding the role of unmanaged arthropod flower visitors as crop pollinators is critical if robust and reliable long‐term alternatives are to be found for honey bee pollination. However, data on pollinator assemblages can be scant. Field observation of crop flower visitors is a common data collection technique but it can be inadequate for species identification and is labour‐intensive if used across many sites. Trapping may reduce this problem, but trap performance and sampling consistency over long distances (sites separated by >100 km) are rarely examined. Window traps were designed to collect flower‐visiting arthropods from peak‐flowering onion (Allium cepa) and pak choi (Brassica rapa var. chinensis) fields across several regions throughout New Zealand. Trap efficacy was evaluated by comparing trapped samples with observations of flower visiting arthropods during the same trapping period, from dawn (6:00 to 7:00 hours) through to dusk (20:00–21:00 hours) at the same locations. Similar types of larger arthropods (length ≥3 mm) were observed and trapped within both crops, with the hymenopteran genera Apidae, Colletidae and Halictidae and the dipteran families Syrphidae, Calliphoridae, Anthomyiidae, Stratiomyidae, Sarcophagidae, Bibionidae, Tachinidae and Muscidae the most commonly recorded. The total counts of these taxa across fields were strongly correlated between the two methods; however, the ratio of trapped to observed individuals could vary greatly between taxa. Trapping allowed more arthropods to be identified to the species level and also helped record more small arthropods (body length <3 mm) when compared with observation. Window traps can be effective for assessing the relative diversity of flower visitor assemblages and the abundance of specific taxa in specific cropping systems at the regional scale, but variation in trap efficiency between arthropod taxa must be assessed for a true measure of assemblage composition.

Insect visitation to flowering hybrid carrot seed crops

“…Crops at site B were commercial seed crops whereas trial plots were utilized at sites A and C. Three sampling methods*sticky traps, water traps and direct observation*were used to identify the insect populations moving around and within the carrots, and those insects that landed directly on the umbels. Howlett et al (2009) similarly used two methods, window traps and direct observations, to study flower visitor assemblages in mass flowering crops. Although direct observations of flower visitors better signifies potential pollinators than those caught on static traps, the use of static traps overcomes the shortfalls of not being able to continuously observe flowers, labour costs and the difficulty of identifying small insects by observation.…”

A review of New Zealand's deliberately introduced bee fauna: current status and potential impacts

“…While acknowledging the potential for fl oral resource competition, Donovan (1980) concluded that anthropogenic factors, such as land disturbance through agriculture and the removal of native vegetation, are more likely to infl uence native bee abundance than competition with honey bees. Several native bees species have also been observed exploiting pollen and nectar resources alongside honey bees on introduced plants such as onion and Brassica rapa (Howlett et al 2005;2009a). Competition for nesting sites does not occur as native species are ground nesting (Leoiproctus and Lasioglossum spp.)…”

Economics of beekeeping as pollination management practices adopted by farmers in Chitwan district of Nepal

“…Promoting use of beekeeping for pollination of agricultural crops will be of benefit to both the beekeeper and the farmer. A large number of pollinators visit Brassica flowers [36][37][38] and these visits play a central role in the resulting quality and yield of seed [39].…”