Variation in the trophic morphology of Astigmatid mites common in UK beehives

Abstract

The chelal moveable digit in Carpoglyphus lactis (Linnaeus), Glycyphagus domesticus (DeGeer), and Tyrophagus putrescentiae (Schrank) from UK beehives is described using quantitative measures within a 2D mechanical model. The location of maximum jerk on the profile of the chelal moveable digit indicates the end of the mastication surface, which in these mites is confirmed to be just before the theoretical cut-off point for a functioning chewing `machine`. All three species should be able to grasp yeasts, spores and mycelial hyphae in the hive. The moveable digit of C. lactis may be designed to enable pollenophagy. The mastication surface is 21.3 μm in C. lactis, 18.8 μm in G. domesticus, and 17.2 μm in T. putrescentiae. The wild-collected C. lactis shows the smallest chelal moveable digit tip velocity ratios (i.e., the lowest relative length of input to output moment arms). Glycyphagus domesticus has the most primitive geometry of its chela. The depth of the moveable digit matches the inferred resistive forces applied by the mite to food at that point. Condylar and moveable digit strengthening by sclerotisation is associated with eating tougher food. Effective chelal gape is 28.7 μm in C. lactis, 25.9 μm in G. domesticus and 24.8 μm in T. putrescentiae. Maximum food fragment size grabbed by the chela is estimated as 7786 μm3 in C. lactis, 5348 μm3 in G. domesticus and 4703 μm3 in T. putrescentiae. Morsel size pre-ingestion is estimated as 4031 μm3 in C. lactis, 5228 μm3 in G. domesticus and 4246 μm3 in T. putrescentiae. Under reasonable assumptions one of these mites might be able to excavate its own body volume equivalent in about one hour.