General

Biodiversity and biological control

Agricultural intensity on the local field or farm scale and on the regional landscape scale affects the organisms utilizing the arable landscape, and may affect ecosystem services and functions. This thesis examines how plants, birds, community composition of ground beetles, and biological control of cereal aphids are affected by local agricultural intensity, organic farming and the surrounding landscape in Sweden and across Europe. The contribution of naturally occurring predator groups to the control of cereal aphid populations in complex and simple arable landscapes is also examined.

Drastic historic shifts in bumble-bee community composition

The species richness of flower-visiting insects has declined in past decades, raising concerns that the ecosystem service they provide by pollinating crops and wild plants is threatened. The relative commonness of different species with shared ecological traits can play a pervasive role in determining ecosystem functioning, but information on changes in abundances of pollinators over time is lacking. We gathered data on relative abundances of bumble-bee species in Swedish red clover fields during three periods in the last 70 years (1940s, 1960s and present), and on clover seed yields since 1921.

Decreased Functional Diversity and Biological Pest Control in Conventional Compared to Organic Crop Fields

We assessed 30 triticale fields (15 organic vs. 15 conventional) and recorded vascular plants, pollinators, aphids and their predators. Organic fields had five times higher plant species richness and about twenty times higher pollinator species richness compared to conventional fields. Abundance of pollinators was even more than one-hundred times higher on organic fields. In contrast, the abundance of cereal aphids was five times lower in organic fields, while predator abundances were three times higher and predator-prey ratios twenty times higher in organic fields, indicating a significantly higher potential for biological pest control in organic fields.

Reconstruction of historical pollination rates reveals linked declines of pollinators and plants

Widespread reports of low pollination rates suggest a recent anthropogenic decline in pollination that could threaten natural and agricultural ecosystems. Nevertheless, unequivocal evidence for a decline in pollination over time has remained elusive because it was not possible to determine historical pollination rates. Here we demonstrate a widely applicable method for reconstructing historical pollination rates, thus allowing comparison with contemporary rates from the same sites. We focused on the relationship between the oil-collecting bee Rediviva peringueyi (Melittidae) and the guild of oil-secreting orchid species (Coryciinae) that depends on it for pollination. The guild is distributed across the highly transformed and fragmented lowlands of the Cape Region of South Africa.

A decline in pollinator dependent vegetable crop productivity in India indicates pollination limitation

Approximately 70% of the tropical crop species depend on pollinators for optimum yields. The economic value of such pollinated crops to India is $726 million and India is the world’s second largest vegetable producer. This status has been underpinned by large-scale changes in land-use and pesticide dependency. A method that partitions crops into categories depending on their relative pollinator dependence (Index of pollinator dependence, DI) was applied to analysis of vegetable yields for India over 45 years (1963-2008) using FAO data. This has revealed that since 1993, relative yields of crop production has either flattened or declined, while pollinator non dependent crops show no similar decline.

90 percent of the 250,000 flowering species now in existence rely on pollinators

Pollinators are an essential part of a garden; so essential in fact, that 90 percent of the 250,000 flowering species now in existence rely on them according to the University of Georgia. Bees and butterflies make up the largest group of pollinators; however, the interior design of certain types of flowers makes it impossible for bees or butterflies to pollinate. These plants must rely on other types of insects to seek out the nectar they produce and pollinate them in the process.

Lower pollinator numbers herald crisis

New Delhi: Red Pierrot, Common Lime, Plain Tiger, Blue Pansy or the Common Castor may be unfamiliar names to most Indians, although it is likely that most would have seen one or more of the five—the most common butterflies found in India. While it is unlikely that most people would notice their absence, it is almost certain that plants will—butterflies, such as these, help them reproduce. The subcontinent has approximately 1,300 of more than 20,000 butterfly species known, said Kishen Das, a US-based lepidopterist. That’s about 6.5% of the global butterfly diversity. However, the problem is that around 100 of the butterfly species found in India are nearing extinction, according to Surya Prakash, a professor at the department of life sciences at Jawaharlal Nehru University. “Few are aware of the crucial pollination role the butterfly plays, which is second only to the honeybee,” he adds.

Achteruitgang van hommelsoorten heeft een negatieve werking op de zaadopbrengst van de rode klaver

De rode klaver (Trifolium pratense) is een overblijvende plant uit de vlinderbloemenfamilie (Leguminosae ofwel Fabaceae). De rode klaver werd vroeger veel gebruikt als voedergewas en komt nu weer meer in de belangstelling voor de ecologische landbouw. Rode klaver wordt nu nog wel geteeld als stoppelgewas, dat wil zeggen dat de rode klaver in maart en april onder graan wordt gezaaid en na de oogst van het graan verder groeit. De bloemen hebben erg nauwe kelkbuizen. Daarom kan de rode klaver niet door bijen bestoven worden. Zij kunnen niet in de nauwe opening. De rode klaver kan wel bestoven worden door een hommel. Een hommel heeft een uitrolbare tong en kan daarmee gemakkelijk in de nauwe kelkbuis komen. Zweedse wetenschappers hebben onlangs aangetoond dat de achteruitgang van hommelsoorten sinds de jaren 1940 een negatieve invloed op de zaadopbrengst van de rode klaver heeft.

De Knautiabij en de Beemdkroon gaan beide achteruit

Beemdkroon (Knautia arvensis) is een wilde plant die stuifmeel en nectar levert aan een breed scala aan insecten. Eén bezoeker, de Knautiabij, Andrena hattorfiana, voedt haar jongen exclusief met stuifmeel van deze plant. Zowel de bij als de plant zijn recentelijk achteruit gegaan, in zowel Nederland als Engeland. Beemdkroon is nog steeds redelijk algemeen, maar al veel minder dan enkele decennia geleden. De afwezigheid van de bij zou een rol kunnen spelen in de achteruitgang van de plant. Een Zweedse studie toonde aan dat de Knautiabij een effectievere bestuiver van de Beemdkroon is dan andere bijen en zweefvliegen.

Gespecialiseerde bijen van wilde klavers hebben het zwaar

De analyse in een studie gepubliceerd in Science laat zien dat wilde bijen die gespecialiseerd zijn op wilde vlinderbloemigen achteruitgaan. Als voorbeeld kunnen de Langhoornbijen dienen (Eucera nigrescens en Eucera longicornis). Deze soorten zijn sterk achteruitgegaan. De Zuidelijke langhoornbij Eucera nigrescens is in Engeland zelfs uitgestorven en wordt in Nederland sterk bedreigd. Dit kan een gevolg zijn van een afname in sommige voedselplanten (Wikke, Lathyrus, Klaver).

Link naar het Science artikel: www.sciencemag.org/cgi/content/short/313/5785/351