Abstract:
A study was undertaken to assess (a) temporal patterns of insect activity and diversity, (b)
evaluate the measures of biological diversity and, (c) identify possible indicator groups of
total insect diversity in an agroecosystem at GKVK Campus, University of Agricultural
Sciences, Bengaluru. The study used light traps to collect insects from 8th May, 2015 to
6th December, 2016 at 21 day intervals. A total of 209,098 individuals belonging to 764
morpho-species or Operational Taxonomic Units (OTUs), representing 101 families from
12 orders were collected. The Simpson’s index of diversity was 0.9732, the Shannon-
Wiener index was 4.4443 and Avalanche index was 1.1693. Five orders, viz., Coleoptera,
Hemiptera, Lepidoptera, Diptera and Hymenoptera dominated the collections. The
relative proportions of these five orders at GKVK agroecosystem were different from
those of the global and Indian insect communities; Coleoptera was over represented at
GKVK while Lepidoptera, Diptera and Hymenoptera were under represented. Order
Coleoptera was found to be a good indicator of the total insect diversity and this perhaps
is because it was the most predominant component of the collections. The study
recommends that light traps may be used for addressing broad ecological questions and to
estimate the total insect diversity. While Simpson and Shannon-Weiner indices were
strongly correlated with the species richness, Avalanche Index (AI) was not; probably
because the biological heterogeneity that AI captures was not strongly reflected in species
richness.Insect diversity and abundance was higher during summer and post monsoon
and less during winter and rainy seasons. Rainfall and relative humidity over three days
negatively affected the insect diversity and activity. Temperature cumulated over three
week period negatively impacted the species richness though the abundance was not
affected. Width of body increased with length at higher rate in Coleoptera and Hemiptera
than Hymenoptera and Diptera suggesting that the former tend to become broader than
the later. Coleoptera also had higher rate of increase in body weight with length probably
due to the elytra. We have argued that insects adopt varying degrees of the two
competing strategies for their protection: Thickening of forewing and adoption of flight
agility. While Coleoptera and Hemiptera adopt the former, the Lepidoptera, Diptera and
Hymenoptera adopt the later strategy.
