The ecology of Sminthurus viridis (L.) (Collembola). I. Processes influencing numbers in pastures in Western Australia

Abstract

The changes in numbers of Sminthurus viridis (Collembola: Sminthuridae) in pastures in Western Australia were studied for 9 years on one site and for shorter periods on other sites. Five factors affecting numbers are described: (1) weather, (2) soil type (3) botanical composition of the pasture, (4) predation by Bdellodes lapidaria (Acarina: Bdellidae), and (5) eating of dead bodies by newly hatched nymphs. Weather is generally favourable for the active stages during autumn, winter, and spring. In the summer, the species is maintained by aestivating eggs. Dry periods during the winter months sometimes cause high mortalities. Soils containing a high silt-plus-clay content support higher numbers due mainly to increased oviposition. Flea densities increase more rapidly where there is a high proportion of broad-leaved plants, such as clover and capeweed in the pasture. Grassy areas are not favoured. Predation by B. lapidaria effectively reduces numbers. The presence of more than 20 B. lapidaria per square metre early in the winter prevents any outbreak of fleas later in the season. Bdellodes lapidaria numbers increase in response to an increase in flea numbers. An irregular predator-prey cycle is set up in this way. Density-induced mortality, resulting from the newly hatched nymphs eating the bodies of recently dead fleas, plays a dominant role at high densities. This process operates continuously though at decreased intensity at lower densities. When newly hatched nymphs feed upon dead nymphs and adults they ingest materials which cause early death. Sometimes this may lead to a dramatic collapse of the population. Fleas from high-density populations usually contain large quantities of uric acid in their "fat-bodies". It is suggested that death of the mature fleas at high densities is hastened through the storage of excessive amounts of waste material. Death of the young nymphs feeding upon the dead bodies may be brought about by the ingestion of these waste materials, although this has yet to be proven.

A RE‐EXAMINATION OF THE DISTRIBUTION OF THE PASTURE SNOUT MITE, BDELLODES LAPIDARIA (KRAMER) (ACARI: BDELLIDAE) AND THE LUCERNE FLEA, SMINTHURUS VIRIDIS (L.) (COLLEMBOLA: SMINTHURIDAE) IN TASMANIA

“…Because B. lapidaria is considered to play an important role in determining S. viridis population size (Wallace 1967), another more detailed Tasmanian survey was begun after population studies on the north-west coast during 1976 suggested that B. lapidaria might be limited in its ability to control populations of S. viridis in this area (Ireson unpub. data).…”

Population Dynamics and Diapause Response of the Springtail Pest Sminthurus viridis (Collembola: Sminthuridae) in Southeastern Australia

“…viridis Emergence. Although the timing of S. viridis emergence from diapause eggs is variable, it also may be potentially predictable, with previous studies highlighting temperature and rainfall as important factors in promoting emergence (Davidson 1934, Wallace 1967. We examined the relationship of these climatic factors with S. viridis emergence observed in this study and compared this relationship with historical data sets.…”

“…Previous studies have consistently found two peak abundance periods that result from autumn emergence of the Þrst generation and then from favorable spring conditions (Davidson 1934, Wallace 1967, Bishop et al 2001a). However, considerable variation has been observed for the number of generations that occur, with between three and Þve relatively distinct generations reported (Davidson 1934, Wallace 1967, Bishop et al 2001a).…”

“…Importantly, the diapause response of S. viridis also may be a potential target for control strategies. However, this requires a strong understanding of the S. viridis life cycle in Australia and despite previous investigations (Davidson 1934, Wallace 1967, Bishop et al 2001a, there is still ambiguity around the life cycle and a lack of current research. Furthermore, in the last decade S. viridis has signiÞcantly increased in prominence and has expanded its distribution in Australia (Bishop et al 1991).…”

“…However, considerable variation has been observed for the number of generations that occur, with between three and Þve relatively distinct generations reported (Davidson 1934, Wallace 1967, Bishop et al 2001a). In addition, the timing of emergence and cessation of the active stage can vary greatly between seasons and locations (Wallace 1967), whereas Bishop et al (2001a) observed hatching of nymphs throughout summer in irrigated lucerne, Medicago sativa L. This apparent plasticity in the S. viridis life cycle also may inßuence its diapause response. Since Þrst being demonstrated by Holdaway (1927), one study by Wallace (1968) has examined diapause in S. viridis in detail.…”