Asia Center go to the web site of The Academy of Natural Sciences

Asia Center of The Academy of Natural Sciences

Terrestrial Insects

Yadamsuren Oyunchuluun

Introduction

Tipulids (Diptera) are a highly diverse group of soil insects that feed on soil organic material, such as leaves of trees. They include several endemic species in the Hövsgöl basin. There appears to be a high positive correlation between soil moisture and tipulid species richness. Crane flies act primarily as detritivores in the terrestrial steppe environment and are dependent on leaf litter for development, which can be affected by amount of grazing pressure, climate and other factors (possibly plant composition). Because of their soft larval bodies, they require moist and non-compacted soils. Adult crane flies feed little, but may be dependent on vegetative structure for protection against predators.

In contrast, the diversity and abundance of grasshoppers appears to be greater in dry habitats, presumably associated with high survival of eggs. At the same time, grasshoppers can have a significant impact on pasture vegetation because they are herbivorous and are in direct competition with grazing livestock.

Objectives

  • Monitoring of insect biodiversity of two important terrestrial steppe insect groups (Orthoptera and Tipulidae identified to species, where possible).
  • Distribution and abundance of insect groups and their association with soil moisture and distribution of vegetation types.
  • Define physical habitats of the species (soil moisture and vegetation) and how widespread larvae of taxa are in a range of habitats.
  • Definition of livestock impacts on the insect taxa.
  • Insect diet study.
  • Observation of grasshopper impacts on the pasture.

Research methods

Petluk box

In order to define insect density in unit area, we used a one-quarter meter square Petluk box. The box is placed at randomly selected points in the steppe where steppe vegetation is also sampled. All collected insects are counted and then multiplied times four to equal number per 1 m2. Grasshopper samples were collected from the 28 plots in the four strata of each of the six valleys.

Aerial sweeping

This method is used to provide measurement of a site’s species diversity, relative abundance, and habitat use by adults. Using a timed-effort approach, the data can be semi-quantitative and compared between sites, but it is difficult to determine the exact unit-area sampled.

Malaise trapping

This method is used to provide measurement of the sites’ species diversity, relative abundance, and habitat use by adults. The data can be semi-quantitative and compared between sites but it is difficult to determine the exact unit-area sampled. Two malaise traps were set in the each valley in the upper steppe and in the riparian zone. Samples are collected in 80% ethyl alcohol and removed at intervals of at least two weeks during May to September. Adult insects in the samples are sorted to the following categories: mayflies, stoneflies, caddisflies, crane flies, chironomids, other aquatic insect groups, orthoptera, and miscellaneous groups (all remaining insects). The aquatic groups (except chironomids), Orthoptera and crane flies are identified and counted. The miscellaneous groups are placed in a bottle, labelled and archived for future identification and analysis.

Larval crane fly sampling

Sampling of the diversity and abundance of terrestrial crane fly larvae in the vegetative zones should be carried out at least 3 times per season in each of the stream valleys (May/June, July/August, and September/October) or following the sampling schedule set by the entire research crew (plant ecology, soil chemistry and other specialists). After sampling the adults and plant biodiversity/biomass and litter layer in a selected plot, the soil is dug to a depth of 3 cm. The soil is broken up by hand and sieved. All insects encountered are preserved in ethanol, and tipulid larvae are counted, identified if possible, and length and width measurements are made for the larvae. All samples are labeled following SOP protocols and the remainder of the sample archived for later analysis or identification.

Findings

Research activities

  • For the field survey the samples are collected along the riparian zone of the upper, middle and lower site of each stream and from different biotopes for crane fly by sweep net. Grasshopper samples are collected from transects in each of the six valleys from 28 plots in four strata. We estimate species abundance (1 hour collection) and collect grasshopper samples per square meter and crane fly samples as a timed collection. Two malaise traps were set up in two different habitats (river bank and forest edge) in each valley. Malaise trap samples were gathered every week from each valley. This method is used to provide measurement of the sites’ species diversity, relative abundance, and habitat use by adults.
  • Grasshopper’s egg and immature crane fly studies may be sensitive to soil compaction, temperature and moisture contents. Grasshopper egg and crane fly larval survey is used to determine the insect’s physical habitat and relationship to soil conditions.
  • Terrestrial insect study considers the spatial and temporal dynamics of quantitative (species composition, dominant and indicator species, relative abundance and taxa richness, similarity index) and qualitative (ecological group, e.g.) parameters of target insect community associated with vegetation and soil moisture.
  • Perform graphical and statistical analysis of all data and relate to other studies (plant biomass, and meteorology).
  • Collaborators:
    • Dr.J.Gelhaus, Entomologist, Academy of Natural Sciences, Philadelphia (USA)
    • Dr. C. H. Chuluunjav, Mongolia
    • Dr. Sagitas Podenas and Dr. Virginia Podeniae, Lithuania
    • Dr. Clyde Goulden, Hovsgol GEF project International Consultant
    • Dr. Peter Petraitis, University of Pennsylvania.

Initial results

  • Fifty species including nineteen subgenera were recorded by the GEF project research in 2002-2003. Nineteen of these species are new for Hövsgöl. (Making a total of 102 for the Hövsgöl basin), and eight new for Mongolia (a total of 142 species).
  • Taxa richness of crane flies is significantly different among the six valleys.
  • The abundance of Orthoptera was significantly different among the study valleys (p<0.01). In the heavily grazed area, the abundance of Orthoptera was significantly higher than the ungrazed and lightly grazed area.
  • Distribution of Tipulids and Orthoptera is directly (Tipulids) or indirectly (grasshoppers) related to soil moisture conditions.
  • There is inverse distribution of grasshoppers and crane flies associated with soil moisture by valleys. As a result of the heavy grazing there is decrease in plant cover and soil moisture. Most crane flies are associated with moist environments, therefore, the heavy grazed area is not optimal condition for them, but it is a good habitat for grasshoppers. Grasshoppers are xerophytes insects.
  • Therefore, it can be concluded that the Tipulids are good indicators of undisturbed soil with high soil moisture but the grasshoppers appear to be good indicators of dry soils and therefore do well in grazed areas.

top of page

Asia Center at The Academy of Natural Sciences
1900 Benjamin Franklin Parkway, Philadelphia, PA 19103 | cgoulden@ansp.org