Abstract
BackgroundCorrect species identification of blow flies is a crucial step for understanding their biology, which can be used not only for designing fly control programs, but also to determine the minimum time since death. Identification techniques are usually based on morphological and molecular characters. However, the use of classical morphology requires experienced entomologists for correct identification; while molecular techniques rely on a sound laboratory expertise and remain ambiguous for certain taxa. Landmark-based geometric morphometric analysis of insect wings has been extensively applied in species identification. However, few wing morphometric analyses of blow fly species have been published.MethodsWe applied a landmark-based geometric morphometric analysis of wings for species identification of 12 medically and forensically important blow fly species of Thailand. Nineteen landmarks of each right wing of 372 specimens were digitised. Variation in wing size and wing shape was analysed and evaluated for allometric effects. The latter confirmed the influence of size on the shape differences between species and sexes. Wing shape variation among genera and species were analysed using canonical variates analysis followed by a cross-validation test.ResultsWing size was not suitable for species discrimination, whereas wing shape can be a useful tool to separate taxa on both, genus and species level depending on the analysed taxa. It appeared to be highly reliable, especially for classifying Chrysomya species, but less robust for a species discrimination in the genera Lucilia and Hemipyrellia. Allometry did not affect species separation but had an impact on sexual shape dimorphism.ConclusionsA landmark-based geometric morphometric analysis of wings is a useful additional method for species discrimination. It is a simple, reliable and inexpensive method, but it can be time-consuming locating the landmarks for a large scale study and requires non-damaged wings for analysis.
Highlights
Correct species identification of blow flies is a crucial step for understanding their biology, which can be used for designing fly control programs, and to determine the minimum time since death
Wing size is known to be affected by environmental factors [27, 34] and our results clearly show that size cannot be used to separate blow fly species
While the percentage of correctly classified specimens from the cross-validation test was very high within Chrysomya (>90.6%), wing shape largely overlapped within Lucilia and Hemipyrellia spp., leading to a much lower percentage of correct assignment (33.3–87.5%)
Summary
Correct species identification of blow flies is a crucial step for understanding their biology, which can be used for designing fly control programs, and to determine the minimum time since death. The use of classical morphology such as bristles on the body or male genitalia are very difficult to apply for non-experts and DNA identification can still remain ambiguous as, for example, some forensically important fly species are not, or insufficiently, represented in the reference libraries [16], many of the existing sequences in those online libraries just represent “dark taxa”, i.e. they are not identified to species level [17], and DNA barcodes failed to distinguish among certain closely related species [14, 18,19,20,21]. This problem is even more serious in regions, where the accurate knowledge of relevant species is a challenge
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