Antennal and palpal sensilla of three predatory Lispe species (Diptera: Muscidae): an ultrastructural investigation

Abstract

Antennae and maxillary palps are the most important chemical reception organs of flies. So far, the morphology of antennae and maxillary palps of flies of most feeding habits have been well described, except for that of relatively rare aquatic predatory species. This study describes sensilla on antennae and maxillary palps of three aquatic predatory Lispe species: Lispe longicollis, L. orientalis and L. pygmaea. Types, distribution, and density of sensilla are characterised via light and scanning electron microscopy. One type of mechanoreceptors is found on antennal scape. Mechanoreceptors (two subtypes) and one single pedicellar button (in L. pygmaea) are located on antennal pedicel. Four types of sensilla are discovered on antennal postpedicel: trichoid sensilla, basiconic sensilla (three subtypes), coeloconic sensilla and clavate sensilla. A unique character of these Lispe species is that the coeloconic sensilla are distributed sparsely on antennal postpedicel. Mechanoreceptors and basiconic sensilla are observed on the surface of maxillary palps in all three species. We demonstrated clear sexual dimorphism of the maxillary palps in some of the Lispe species, unlike most other Muscidae species, are larger in males than females. This, along with their courtship dance behaviour, suggest their function as both chemical signal receiver and visual signal conveyer, which is among the few records of a chemical reception organ act as a signal conveyer in insects.

Figure 1

Features on heads and antennae of adult Lispe longicollis, L. orientalis and L. pygmaea. Frontolateral view of (a) male L. longicollis, (c) L. orientalis, and (e) L. pygmaea heads by stereoscopic microscope. SEM micrograph of (b) male L. longicollis, (d) L. orientalis, and (f) L. pygmaea antenna, showing the posterior surface. Ar arista, Mp maxillary palp, Pd pedicel, Ppd postpedicel, Sc scape. Scale bars: (a,c,e) = 500 μm; (b,d,f) = 150 μm.

Figure 2

SEM micrographs of features on the antennal scape and pedicel of adult Lispe longicollis, L. orientalis and L. pygmaea. (a) Anterior surface of antennal scape and pedicel of male L. longicollis, arrows showing mechanoreceptors. (b) Anterior surface of antennal scape and pedicel of male L. orientalis, arrows showing mechanoreceptors. (c) Mechanoreceptors on antennal scape of male L. pygmaea. (d) Pedicellar button of male L. pygmaea. Mr mechanoreceptors, Mr I subtype I mechanoreceptor, Mr II subtype II mechanoreceptor, Mt microtrichia, PB pedicellar button. Scale bars: (a,b) 50 μm; (c) 10 μm; (d) 5 μm.

Figure 3

SEM micrographs of features on antennal postpedicel of male Lispe longicollis. (a) Posterior surface of antennal postpedicel. (b) Distribution of different types of sensilla on antennal postpedicel. (c) Trichoid sensilla, box showing micropores on the surface. (d) Subtype I basiconic sensilla, box showing micropores on the surface. (e) Subtype II basiconic sensilla, box showing micropores on the surface. (f) Subtype III basiconic sensilla, box showing micropores on the surface. (g) Coeloconic sensilla. (h) Clavate sensilla, box showing micropores on the surface. Ba I subtype I basiconic sensilla, Ba II subtype II basiconic sensilla, Ba III subtype III basiconic sensilla, Co coeloconic sensilla, Cl clavate sensilla, Mt microtrichia, Tr trichoid sensilla. Scale bars: (a) 150 μm; (b) 10 μm; (c–f) 2.5 μm, 0.5 μm in box; (g) 2.5 μm.

Figure 4

SEM micrographs of features on antennal postpedicel of male Lispe orientalis. (a) Posterior surface of antennal postpedicel. (b) Distribution of different types of sensilla on antennal postpedicel. (c) Trichoid sensilla, box showing micropores on the surface. (d) Subtype I basiconic sensilla, box showing micropores on the surface. (e) Subtype II basiconic sensilla, box showing micropores on the surface. (f) Coeloconic sensilla. (g) Clavate sensilla, box showing micropores on the surface. Ba I subtype I basiconic sensilla, Ba II subtype II basiconic sensilla, Co coeloconic sensilla, Cl clavate sensilla, Mt microtrichia, Tr trichoid sensilla. Scale bars: (a) 150 μm; (b) 10 μm; (c–e,g) 2.5 μm, 0.5 μm in box; (f) 2.5 μm.

Figure 5

SEM micrographs of features on antennal postpedicel of male Lispe pygmaea. (a) Posterior surface of antennal postpedicel. (b) Distribution of different types of sensilla on antennal postpedicel. (c) Trichoid sensilla, box showing micropores on the surface. (d) Subtype I basiconic sensilla, box showing micropores on the surface. (e) Subtype II basiconic sensilla, box showing micropores on the surface. (f) Subtype III basiconic sensilla, box showing micropores on the surface. (g) Coeloconic sensilla. (h) Clavate sensilla, box showing micropores on the surface. Ba I subtype I basiconic sensilla, Ba II subtype II basiconic sensilla, Ba III subtype III basiconic sensilla, Co coeloconic sensilla, Cl clavate sensilla, Mt microtrichia, Tr trichoid sensilla. Scale bars: (a) 150 μm; (b) 10 μm; (c–f,h) 2.5 μm, 0.5 μm in box; (g) = 2.5 μm.

Figure 6

SEM micrographs of features on maxillary palps of Lispe orientalis and L. pygmaea. (a) Posterior surface on maxillary palp of male L. orientalis. (b) Posterior surface on maxillary palp of male L. pygmaea. (c) Different types of sensilla on maxillary palp of male L. orientalis. (d) Different types of sensilla on maxillary palp of male L. pygmaea. (e) Subtype IV basiconic sensilla of male L. orientalis. (f) Subtype IV basiconic sensilla of L. pygmaea. Mr III subtype III mechanoreceptor, Mt microtrichia, Ba IV subtype IV basiconic sensilla. Scale bars: (a,b) = 100 μm; (c,d) = 20 μm; (e,f) = 5 μm.

Figure 7

Two-way ANOVA results of characters of maxillary palps among three Lispe species and sexes. (a) Swelling degree of maxillary palps of the three species among three species and sexes. Male L. orientalis has significantly larger swelling than females (F_5,24 = 39.99, P < 0.001; species: F_2,24 = 77.05, P < 0.001; sex: F_1,24 = 18.96, P < 0.001; species × sex: F_2,24 = 13.44, P < 0.001). (b) The ratio of maxillary palp length to body length (LMP/BL) among three species and two sexes. Male L. orientalis has significantly longer maxillary palps than females (F_5,24 = 3.98, P = 0.0090; species: F_2,24 = 3.49, P = 0.05; sex: F_1,24 = 1.41, P = 0.25; species × sex: F_2,24 = 5.75, P = 0.0091). (c) The ratio of maxillary palp width to body length (WMP/BL) among three species and two sexes. Male L. orientalis has significantly wider maxillary palps than females (F_5,24 = 63.58, P < 0.001; species: F_2,24 = 111.78, P < 0.001; sex: F_1,24 = 34.23, P < 0.001; species × sex: F_2,24 = 1.26, P < 0.001). Different lower-case letters mean significant differences.