International Symposium

The Suffolk Argus

Butterfly Conservation’s International Symposium

‘The 2010 Target and Beyond for Lepidoptera’ was the theme for the 6th International Symposium held at Reading University, during the 26th-28th March 2010.

Welcomed by an inspiring speech from Sir David Attenborough, 250 delegates from Britain, continental Europe, America, Africa and Japan attended lectures on subjects that ranged across topics such as ‘British Butterfly Distribution and the 2010 Target’ , ‘How are Butterflies Doing in Europe?’ , ‘Countryside Moth Conservation’ and ‘Butterfly Response to Climate Change’ .

Rob Parker shares some of his gleanings from the Symposium

Larval Habitat Needs Various speakers drew attention to very precise needs for successful completion of the larval stage. Egg-laying criteria were very precise, and larval survival depended on a variety of factors. Optimal habitat was needed particularly at the margins of range. Some factors: niche microclimate, aspect, shelter, soil type, drainage, sun or shade, sward height, temperature (optima differ for species), quantity of larval host plant(s), quality of larval host plant’s growth & situation (sprawling over rocks, climbing up other vegetation), predation by host-specific parasites, casual grazing, management.

Site Quality Site size was considered less important than site diversity. Sites with optimum habitat often have the carrying capacity to support populations a hundred times as great as “suitable sites” , and the difference is often not readily apparent to the human eye. Adonis Blue often prefers to lay in short sward in preference to “perfect looking” adjacent patches loaded with nectar and larval host plants. Sites with general diversity and high species counts also have high numbers (butterflies/acre).

Abandonment leads to scrub encroachment and progressive loss of diversity. This can be measured at suitable sites (an Estonian island was assessed) and floral & faunal degradation was quite rapid. Declines in butterfly populations were noticeable before floral decline was detected. Abandonment is occurring across Eastern Europe as smalltime farmers give up and move to towns. In some ways, planting of trees in former grassland in UK as “conservation areas” can amount to abandonment of grassland habitat.

The decline of nectar sources is a general phenomenon driven by eutrophication and has a direct impact on bee and butterfly abundance. Actually, the rate of nitrogen deposition has been reduced over the past decade, but the effects are presumably cumulative.

Extinction Debt Progressive degradation has inertia, and

loss of diversity is not easily checked – thus extinctions may become inevitable and conservation effort will be doomed to failure if left too late. The converse is that there is a time lag before conservation effort leads to results. The invertebrate fauna of a site is more closely related to the historic flora than to the present situation.

Field Margins At least 4 speakers covered the topic of agrienvironmental schemes and assessing the benefits to insects. A long running scheme in the lowlands of Switzerland is proving very effective, and seems (to me) much better than ours. Its key features are that farmers are encouraged to plant strips sown with a locally standardised mix of 24 wildflowers with zero grass. (OK, it must be more expensive than ours too!). Often these strips are left without further management until the rules demand that they are ploughed after 7 years. These strips supported 25 of the 38 species found locally (plus the Mallow Skipper, not normally considered local, appeared because mallow was one of the plant species). Old meadows nearby were treated as controls, and the species found there were somewhat different, due to LHP availability, presumably.

Finnish studies found that nectar & pollen mixes outperformed standard mixes, as did a grass mix composed of less competitive varieties. Strips alongside wooded margins invariably outperformed open field strips, particularly for moths, although generally, butterflies colonised before moths. Mid-field strips attracted many butterflies when in flower, whereas field margin strips retained their butterfly populations throughout the season. Mowing appeared to improve butterfly diversity.

An interesting study by Robin Blake, at Reading University ’s Centre for AgriEnvironmental Research, used an application of a selective graminicide on existing grass buffer strips. The graminicide (fluazipop-P-butyl) kills competitive grasses, but leaves finer grasses like

fescues unharmed and creates a germination niche for wildflowers. Trials with and without scarification, with and without wildflower sowing are showing great promise as a means of enhancing the biodiversity of the 29,000 ha of existing grass buffer strips in UK. Buffer strips have been a popular option in UK because they are cheap, but the lack of nectar limits their biodiversity value.

It was observed that sowing yellow rattle would also be an enduring way of suppressing competitive grasses, perhaps after an initial graminicide treatment.

Mowing the Meadow Browns away In Belgium farmers are required to leave a shelter zone of 5% of each hay field when mowing the crop. A study of the impact on butterflies of the sudden reduction in nectar availability involved filming knapweed plants before and after mowing, and tracking the movements of associated Meadow Browns. I was interested to discover that females used the shelter zone for nectar sources, but also make excursions well into the mown area to lay eggs there.

Purple Emperor Preferences Matthew Oates’ detailed study of egglaying preference in the Purple Emperor