Parasitoid Density Higher in Farmers’ Ecological Engineering Fields; No Difference in Species Biodiversity in Cai Be, Tien Giang, Vietnam

In Cai Be District we initiate ecological engineering fields through farmer participation.  Thirty-five (35) farmers in a village were encouraged to cultivate several species of nectar rich flowers along the bunds to increase parasitoid biodiversity.

Another area of about 20 ha was left as the control field. We monitored the parasitoids by various sampling techniques described in the ecological engineering sampling protocol.

Here we discuss the analysis of the net sweep sampling collected during the tillering, flowering, and ripening stages of the rice crop.  The samples from a total of 120 net sweep samples (each of 25 sweeps) were pooled and the arthropods sorted into functional groups.

The parasitoid data was analyzed by using biodiversity indices computed by ECOSIM (Gotelli and Entsminger 2005) and EstimateS (Colwell 2006). To avoid sample size sensitivity, the rarefaction technique was applied to compute species richness.

We used the indices that have less sample size sensitivity and with more discriminating abilities for comparison (Magurran 1988).

Table 1 shows the biodiversity indices of the control and ecological engineering fields and the rarefaction curve is also presented.

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Biodiversity monitoring of parasitoids using new sweeps

Table 1: Comparison of parasitoid biodiversity from net sweeps in ecological engineering and control fields of farmers in Cai Be, Tien Giang, Vietnam. 2009.

Biodiversity indicesControl fieldsEcol engineering fields
Species richness, S or Esn (rarefaction)6562.5
Log series index alpha24.923.3
Reciprocal Simpson’s (1/D)0.0550.057
Exp Shannon or Hill N131.830.2
Total number of individuals315447

The biodiversity indices had only slight differences between the ecological engineering and control fields.

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: Rarefaction curves of parasitoids of net sweeps collected in ecological engineering and control fields of farmers in Cai Be, Vietnam

There were  higher numbers of parasitoids caught in ecological engineering fields than in the control fields.  Egg parasitoids of hoppers were most dominant.

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Higher parasitoid densities in ecological engineering fields

The brown planthopper counts were significantly lower in the ecological engineering fields.

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Lower BPH densities in ecological engineering fields

The ecological initiative was launched on September 10, 2010 by Vice Minister Dr Bui Ba Bong to enhance the adoption of ecological engineering concepts and techniques to reduce the vulnerability of rice fields to planthopper outbreaks (Read: Vice Minister launch).

Earlier Nalinee et al wrote about doubling of parasitoid biodiversity from 16 to 30 in ecological engineering plots in Chainat, Thailand (Read: Parasitoid biodiversity increases).  It is possible that the yellow pan trap may be more or less sensitive to parasitoid captures.

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