In search of efficient and effective sampling methods for field evaluation of non-target organisms in Bt corn variety trials: a comparative study

Data gathered from previous studies that involved regulated field trials for Bt corn hybrids MON89034 and MON89034/NK603 in Isabela, Pangasinan and South Cotabato [Philippines] provinces were reviewed and analyzed. The field trials were intended to evaluate the effects of the two new Bt-corn hybrids on non-target organisms (NTOs). Specifically, review of data focused on the sampling methods used, namely, sweep net sampling, visual counting, vacuum sampling, pitfall trapping, sugar baiting and tuna baiting. The methods were compared in terms of their efficiency and effectiveness. The concept of efficiency of a method as the number of individuals captured is adopted from previous studies. However, the concept of a method's effectiveness for arthropod community studies such as those focusing on NTOs is further refined. Taxon effectiveness is proposed to refer to the number of taxa (species, genera, families, orders) detected whereas guild effectiveness would be the number of functional guilds attracted. The methods varied in efficiency and in taxon as well as guild effectiveness. In terms of number of individuals collected (efficiency), the sampling methods ranked, in decreasing order, as follows: tuna baiting visual counting vacuum sampling sweep net sampling pitfall trapping sugar baiting. On the other hand, in terms of number of morpho-species collected (taxon effectiveness), they generally ranked, also in decreasing order, as follows: vacuum sampling visual counting sweep net sampling pitfall trapping tuna baiting = sugar baiting. A more or less similar trend was observed for guild effectiveness. Overall, the number of samples can be reduced to save cost because using the different methods and sampling procedures practically gave the same results. With these significant findings, researchers will be able to lessen the time and duration of sampling, limit collection and sampling to indicator species/group, save cost and have more time to examine and identify specimens up to species level.