Reliability of volumetric and gravimetric methods for estimating the number of Carpophilus spp. (Coleoptera: Nitidulidae) in traps
2009
Hossain, Mofakhar S. | Hossain, Mamun A.B M. | Chandra, Subhash | Williams, David G.
Reliable estimation of insect population size is a pre-requisite to understand population dynamics and to develop management strategies for pest infestations. We report the results of three sampling studies to identify reliable methods of estimating the number of carpophilus beetles in traps. Study 1 compared reliability of volumetric and gravimetric methods. Fresh beetles and beetles dried for 24, 48 and 72 h were used. The reliability in terms of consistency and precision was quantified. A reliable method must first be consistent, quantified by a linear trend of zero slope. Volumetric methods using fresh and 24 h dried beetles were consistent and had good precision. Study 2 investigated the influence of sample size on reliability of volumetric estimation of number of fresh beetles using a 5 mL cylinder. Study 3 examined the influence of cylinder size on reliable volumetric estimation of 1000 fresh beetles. All three sample and cylinder sizes investigated were consistent and had good precision. These results suggest that volumetric methods are generally consistent and possess good precision, a 5 mL cylinder may be used for reliable volumetric estimation of up to 500 beetles, and a 50 mL cylinder may be used for reliable volumetric estimation of larger numbers of beetles. A model is developed to predict the number of fresh beetles from their measured volume. Advantages of volumetric methods compared with gravimetric methods are discussed.
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