Agriculture Reference
In-Depth Information
The superfamily Staphylinoidea comprises several families of importance to the litter and
soil: Staphylinidae, Pselaphidae, Ptiliidae and Silphidae. Adults and larvae of Staphylinidae
are mostly predators which digest their prey by extra-oral digestion, although populations
from the two sub-families Osoriinae and Oxytelinae are fungal feeders. Staphylinidae may
complete their life cycle in a relatively short period of a few weeks to months, and have
several generations per year. Adults may live for several months to years (Newton, 1990).
Dung beetles (Scarabaeinae) may play a critical role in the burial of dung, especially
in relatively dry environments. They dig subvertical galleries 10-15 mm wide, down to
50-70 cm depth, with a variable number of chambers which are further filled with large
pellets of dung; one egg is laid in each pellet and the larva will complete its develop-
mental cycle feeding on the pellet. Excavations are deposited at the soil surface and form
small mounds a few centimetres high (Hurpin, 1962). The shape, depth and number
of chambers of a nest are a species specific characteristic which allows evolutionary
lineages to be discriminated (Halffter and Edmunds, 1981). Elateridae are another
typical family of soil and litter dwelling Coleoptera which are constantly present in
soils and may occasionally become serious pests of field crops (d'Aguilar, 1962).
Arachnida
Finally, a range of predators live largely within litters and, to a lesser extent, in soils.
Arachnida (Opilionidae, Araneidae and some smaller groups) form an extremely diverse
group, which mainly live in the litter with exception of a few burrowing species.
They are predators of Collembola, Enchytraeidae, Acari and many other small litter
and soil invertebrates.
4.3.4.2
Population Densities and Biomasses
Coleoptera generally represent the third or fourth rank of macro-invertebrate biomass in
soils, after earthworms, termites or ants. In dry savannas of South Africa at Nilsvley, they
are the most important group in terms of biomass with values of 7.15 to 8.15 g f wt
depending on the type of savanna (Scholes and Walker, 1993); in humid tropical pastures
of Mexico, mean annual biomass of Coleoptera was 19 g f wt with a peak value
of 60 g at the end of the rainy season; Scarabaeidae Melolonthinae comprised 90 %
of this biomass (Villalobos and Lavelle, 1990). Most biomass values are in the range
50-200 mg dry wt (Petersen and Luxton, 1982). Maximum densities have been record-
ed in an abandoned field in Sweden (1404 ind. ± 189 with a biomass of 2.86 ±4.2 g
dry wt equivalent to 10 g f wt, Persson and Lohm, 1977) and savannas at Lamto (Ivory
Coast) (Athias
et al
., 1975).
Isopoda. Where present, Isopoda generally have low densities of a few tens to a few
hundreds of ind. Maximum values of 1000 to 7900 ind. have been reported for
some British grasslands and forests (Sutton, 1972; Petersen and Luxton, 1982; Molfetas,
1982; Mocquard
et al
., 1987). Species diversity is generally limited to 4-5 species
(Mocquard
et al
., 1987). Densities are particularly low in acid soils with mor-type humus
or where frost or drought occur.
Diplopoda frequently have high population densities of 200 to 500 ind.
in
