Fine structure of the sensilla and immunolocalisation of odorant binding proteins in the cerci of the migratory locust, Locusta migratoria

Abstract

Using light and electron microscopy (both scanning and transmission), we observed the presence of sensilla chaetica and hairs on the cerci of the migratory locust, Locusta migratoria L. (Orthoptera: Acrididae). Based on their fine structures, three types of sensilla chaetica were identified: long, medium, and short. Males presented significantly more numbers of medium and short sensilla chaetica than females (p<0.05). The other hairs can also be distinguished as long and short. Sensilla chaetica were mainly located on the distal parts of the cerci, while hairs were mostly found on the proximal parts. Several dendritic branches, enveloped by a dendritic sheath, are present in the lymph cavity of the sensilla chaetica. Long, medium, and short sensilla chaetica contain five, four and three dendrites, respectively. In contrast, no dendritic structure was observed in the cavity of the hairs. By immunocytochemistry experiments only odorant-binding protein 2 from L. migratoria (LmigOBP2) and chemosensory protein class I from the desert locust, Schistocerca gregaria Forsskål (SgreCSPI) strongly stained the outer lymph of sensilla chaetica of the cerci. The other two types of hairs were never labeled. The results indicate that the cerci might be involved in contact chemoreception processes.

Figure 1.

Spatial map and distribution of sensilla on the cerci of Locusta migratoria. Results from light microscopy (A) and scanning electron microscopy (B) show that there are three types of sensillum chaetica (long s. chaetica (Lc), medium s. chaetica (Mc), and short s. chaetica (Sc)) and two types of hairs (long hairs (Lm) and short hairs (Sm)). The distribution of the three types of s. chaetica and two types of hairs are shown in C and D. Bar: A = 180 µm; B = 200 µm; C, D = 400 µm. High quality figures are available online.

Figure 2.

Fine structure of the long sensilla chaetica of the Locusta migratoria cerci. (A) The longitudinal grooves (g) on the surface are obvious together with a large socket (s) at the base but no pore on the cuticle wall (cw). (B) The groves are evident. (C) The longitudinal sections show the presence of five non-branched dendrites (d) in the inner sensillum lymph (isl). (D) The transverse sections show that the inner sensillum lymph (isl) and the outer sensillum lymph (osl) are separated by a dendritic sheath (sh). (E) Different dendrites vary in their number of microtubules (mt). Bar: A = 50 µm; B = 10 µm; C = 3 µm; D = I µm; E = 143 nm. High quality figures are available online.

Figure 3.

Fine structure of the medium sensillum chaetica of the Locusta migratoria cerci. (A) The longitudinal grooves (g) on the surface are obvious together with a large socket (s) at the base but no pore on the cuticle wall (cw). (B) The pore at the tip (tp). (C) The transverse sections show that the inner sensillum lymph (isl) contains four dendrites (d) enveloped by a dendritic sheath (sh). The outer sensillum lymph (osl) is also labeled. (D) The four dendrites vary in the number of microtubules (mt) from 10 to 20. Bar: A = 10 µm; B = 2 µm; C = I µm; D = 143 nm. High quality figures are available online.

Figure 4.

Fine structure of the short sensillum chaetica of the Locusta migratoria cerci. (A) The longitudinal grooves (g) on the surface are not visible together with a large socket (s) at the base. One pore is present on the tip (tp), but none is evident on the cuticle wall (cw). (B) The transverse section show that the lymph is separated by the dendritic sheath (sh) into the outer sensillum lymph (osl) and inner sensillum lymph (isl). Three nonbranched dendrites (d) are located in the inner sensillum lymph (isl); (C) The dendrites each have around 10 microtubules (mt). Bar: A = 5 µm; B = I µm; C = 125 nm. High quality figures are available online.

Figure 5.

Fine structure of the hairs of the Locusta migratoria cerci. (A) Scanning electron microscopy shows that the long and short hairs have a similar morphology. Both are slight, have obvious longitudinal grooves (g) on the surface and a large cavity (c) at the base but no pore on the cuticle wall (cw). (B) Long and short hairs differ significantly in length. The transverse sections of long (C) and short hairs (D) indicate that there is only one inner cavity (IC) and no dendrites or dendritic sheath. (E) The longitudinal sections show tubular body (tb) and cavity (c). Epidermis is indicated by the abbreviation, ep.. Bar: A = 20 µm; B = 200 µm; C = 1.7 µm; D = 833 nm; E = 1.4 µm. High quality figures are available online.

Figure 6.

Western blot and immunocytochemistry. (A) The recombinant proteins of odorant-binding proteins (OBPs) and chemosensory proteins (CSPs): LmigOBP1, LmigOBP2, LmigOBP3, and LmigCSPII, were separated by 14% SDS-PAGE gels. Molecular weight markers are from the top: BSA (66kDa), ovalbumin (45kDa), carbonic anhydrase (31kDa), trypsin inhibitor (20kDa), and lactalbumin (14kDa). (B) Result of Western blot using the antiserum SgreCSPI after SDS-PAGE together with A. Only LmigOBP1 could not react with anti-SgreCSPI, and other proteins all cross-react with anti-SgreCSPI. (C) Result of Western blot using the antiserum LmigOBP2, SgreCSPI, and LmigCSPII after the recombinant proteins of LmigOBP2 and LmigCSPII separating by SDS-PAGE. LmigCSPII and LmigOBP2 could not cross-react with each other, and SgreCSPI and LmigCSPII cross-react with each other. (D) Immunocytochemistry using the antiserum LmigOBP2 indicated that LmigOBP2 specifically expressed in the outer sensillum lymph of s. chaetica. The cuticle was not specifically labeled. Bar: D = 0.5µm. High quality figures are available online.