Spatial distribution of bibionid larvae in agricultural grassland

Abstract

The distribution of bibionid larvae in agricultural grassland was investigated. They tend to occur sporadically and at low population density. More detailed sampling within a field showed that numbers were highest adjacent to a hedgerow with most being found 6–11 m from the hedge. Log variance/log mean relationships were established for counts of Bibio johannis and Dilophus febrilis larvae collected from soil cores in grassland. Both species were highly aggregated. An area of grassland (160 cm × 80 cm) was divided into 128 soil blocks and B. johannis larvae extracted. Almost all larvae were associated with aggregations. The two‐phase mozaic method of Pielou (1974) was applied to larval counts from different sized concentrically collected soil cores. Larval patches were not randomly distributed. Time‐lapse video studies of bibionid larvae were made and showed both aggregation and processional behaviour. This was associated with chemical stimulation which is probably used to maintain larval groupings in the field. There was evidence for two levels of aggregation. The first is due to groups of larvae arising from eggs laid by a single female and the second, larger scale, aggregation is due to factors that influence the distribution of adult flies.

A review of the ecology and conservation of hedgerow invertebrates in Britain

“…This included mainly mobile field-associated taxa, such as thrips and staphylinid beetles, which may have aggregated near hedges through passive dispersal. Other studies have shown the importance of hedgerow proximity for soildwelling species in fields (Alvarez et al, 1997;Blackshaw and DarcyBurt, 1997), which may also be related to shelter effects. In summer, shelter from wind also produces localised warmer and more humid conditions, compared to open fields, which are favoured by many invertebrate species (Forman and Baudry, 1984).…”

Uso da geoestatística para caracterização da distribuição espacial de larvas de Diloboderus abderus

“…Diversas técnicas têm sido utilizadas para determinar variações espaciais de pragas (BLACKSHAW & ARCY- BURT, 1997;FERNANDES et al, 2002;CAMPBELL & MULLEN, 2004;PARK & TOLLEFSON, 2005;PARK & TOLLEFSON, 2006). Dentre essas, a geoestatística (ELLSBURY et al, 1998;FARIAS et al, 2004;BLACKSHAW & VERNON, 2006;FARIAS et al, 2008), que se fundamenta no princípio de que a diferença no valor de uma dada variável, em dois pontos, é dependente da distância entre esses, estando associada às técnicas usadas para analisar e inferir valores de uma variável distribuída no espaço e/ ou no tempo (GARCÍA, 2006).…”

Patch edges and insect populations

“…Kareiva 1983Kareiva , 1985Marino and Landis 1996;Blackshaw and Arcy-Burt 1997;Svensson et al 2000;Magura 2002), it may be useful to consider the interaction of these factors on the distribution of populations among patches within a landscape. The theory of patch size has concentrated on determining the critical size below which a population will not be able to sustain itself (Slobodkin 1961;Okubo 1984).…”