**7. Sexual dimorphism in antennae of** *Phyllophaga opaca*

*Phyllophaga opaca* is distributed in the states of Michoacan and Sinaloa, Mexico [30]. Some general characteristics of its flight and eating habits [33], the nature of its chemical sexual communication, and the structures involved in the production of its sex pheromone [25] are known, although there are no data regarding of its sexual dimorphism in body and antennae. Although the body of adult *P. opaca* males is very similar in size than the females, the entire male antenna is significantly longer (<0.001) (Figures 2 E-F, Table 1). In males, DL and ML were longer and had a larger area than in females (Table 1). Also, PL in males were longer than in females (Table 1).

PLAS, AUS, BAS, COS, TRS and CHS were observed on *P. opaca* antennae (females and males) using light- and scanning electron-microscopy (Figures 4 and 5). TRS have a long spine- or hair-like structure and CHS present a short-spine, being shorter than TRS (Table 2, Figure 4). For *P. opaca*, fifteen chemo-sensilla types were found: four types of PLAS, four of AUS, five of BAS, and two of COS.

For both sexes, PLAS type I were observed randomly distributed on IN of all lamellae mainly in the center, except on peripheral edges of lamellae; they are rounded and elongated plates (Figures 4C-D, Table 2). PLAS type II were observed in both males and females, randomly distributed on IN of all lamellae mainly in the center; they are spherical

For both sexes, PLAS type I were observed randomly distributed on internal surface (IN) of all lamellae mainly in the center, except on peripheral edges of lamellae. PLAS type II were observed randomly distributed on IN and at the peripheral edges of all lamellae in both male and females. PLAS type III were located on IN of all lamellae, principally on pit, basal, and peripheral edges in both sexes. AUS type I were observed randomly distributed on IN and peripheral edges of all lamellae for both sexes. AUS type II was observed only in male lamellae, distributed on both sides (except on the external surface of the DL). AUS type III was located only on male lamellae, randomly distributed on IN and on peripheral edges (except on the IN of DL). AUS type IV were restricted to the center of PL in males. BAS type I were observed randomly distributed mostly on IN of all club lamellae of both sexes (except on peripheral edges and on the IN of ML). BAS type II are present for both sexes, they are situated on IN and peripheral edges of all lamellae. For both sexes, BAS type III were observed randomly distributed principally on IN of all club lamellae, except on peripheral edges. BAS type IV were found only in females at the center of the IN of ML and PL. BAS type V were found only in males, mainly at the center of the IN of PL. For both sexes, COS type I are restricted principally to the center, appearing only at the IN of all club lamellae. COS type II are located in both sexes, on the floor of cuticle cavities. COS type II are restricted only to females, mostly at the center and only on the IN of all club lamellae, except on DL. COS type III are located inside cavities in the antennal cuticle. COS III are restricted principally to the center, appearing only on the IN of all club lamellae in both sexes, except on male PL. COS type IV are found only in males and are restricted to the center and IN of

PL. They are located inside depressions or cavities in the antennal cuticle.

**7. Sexual dimorphism in antennae of** *Phyllophaga opaca*

longer than in females (Table 1).

AUS, five of BAS, and two of COS.

*Phyllophaga opaca* is distributed in the states of Michoacan and Sinaloa, Mexico [30]. Some general characteristics of its flight and eating habits [33], the nature of its chemical sexual communication, and the structures involved in the production of its sex pheromone [25] are known, although there are no data regarding of its sexual dimorphism in body and antennae. Although the body of adult *P. opaca* males is very similar in size than the females, the entire male antenna is significantly longer (<0.001) (Figures 2 E-F, Table 1). In males, DL and ML were longer and had a larger area than in females (Table 1). Also, PL in males were

PLAS, AUS, BAS, COS, TRS and CHS were observed on *P. opaca* antennae (females and males) using light- and scanning electron-microscopy (Figures 4 and 5). TRS have a long spine- or hair-like structure and CHS present a short-spine, being shorter than TRS (Table 2, Figure 4). For *P. opaca*, fifteen chemo-sensilla types were found: four types of PLAS, four of

For both sexes, PLAS type I were observed randomly distributed on IN of all lamellae mainly in the center, except on peripheral edges of lamellae; they are rounded and elongated plates (Figures 4C-D, Table 2). PLAS type II were observed in both males and females, randomly distributed on IN of all lamellae mainly in the center; they are spherical **Figure 4.** Sensilla on the antennae of female *Phyllophaga opaca*. A) Internal surface (IN) of distal lamella (DL). In the periphery of the lamella, trichodea (TRS) and chaetica sensillum (CHS) are observed. B) Detail of placodea sensilla (PLAS) type III on external (EX) of proximal lamella (PL). C) Coeloconica sensilla (COS) type I, auricilica sensilla (AUS) type I, basiconica sensilla (BAS) type IV and PLAS I on IN of DL. D) Detail of COS I, PLAS I y PLAS II on IN of medium lamella (ML). E) COS I and BAS I on IN of PL. F) Detail of COS I, AUS IV and BAS III on IN of PL. Micrographies by T. Laez.

Sexual Dimorphism in Antennae of Mexican Species of *Phyllophaga* 

or elliptical and thin-walled plates (Figures 4D-5D, Table 2). PLAS type III are located on both sides of all lamellae, principally on pit and peripheral edges in both sexes; they are small, elliptical, thin-walled plates or low dome-shaped plates (Figures 4B-5A, Table 2). PLAS type VIII are chemoreceptors not reported previously; they are spherical or elliptical and thin-walled plates with "human-ear" like structure in the center. PLAS VIII were

AUS type I were observed randomly distributed on IN of all lamellae for both sexes; they are characterized by a "rabbit-ear" shape or elliptical and thin-walled plates (Figures 4C-5C, Table 2). AUS type II were observed only in male lamellae, distributed on IN of ML and DL; they are "rabbit-ear" shaped structures, elliptical and low dome-shaped (Figures 5C-D, Table 2). AUS type III were located only on male lamellae, randomly distributed on IN of lamella center (except on the IN of DL); they are characterized by a "human-ear" shape (Figures 5E, Table 2). AUS type IV were restricted to the center of PL in both sexes; their shape is characterized as "rabbit-ear with neck" or "raisin with neck" structures (Figure 4F,

BAS type I were observed randomly distributed mostly on IN of all club lamellae of both sexes (except on peripheral edges and on the external surface of ML); they are large peg- or cone-shaped (Figures 4E-5B, Table 2). BAS type II are short-spine shaped; for both sexes, they are situated on both sides of all lamellae (Figure 5D, Table 2). BAS type III were observed for both sexes distributed on both sides of all lamellae; they are short-cone shaped (Figures 4F-5A, Table 2). BAS type IV were found randomly distributed on IN of all club lamellae of both sexes of PL and DL; they are serrated-cone shaped (Figures 4C-5B-5F, Table 2). BAS type V were found only in males, mainly at the center of the IN of PL; they are long-

For both sexes, COS type I are restricted principally to the center, appearing only at the IN of all club lamellae. They are found as aggregations of 2 to 16 long peg- or cone-shaped structures (BAS I) located inside depressions or cavities in the antennal cuticle (Figures 4 and 5, Table 2). COS type II were found as aggregations of two to three serrated coneshaped structures (BAS IV) located on the floor of cuticle cavities. These cavities vary in size between 11.58 and 17.54 μm on the largest axis. COS type III are restricted principally to the

As described in this chapter, in the melolonthids there is a marked sexual dimorphism at different levels. In the case of the members of the genus *Phyllophaga*, mainly for Mexican species have been studied some morphological traits that allow differentiate between females and males. For antennae, at least three species studied show sexual dimorphism in body size, length of the antennae and lamellae, and the presence/absence of certain types of sensilla. Sexual dimorphism in antennae of these species is evident when considering antennal/body length ratio. For *P. obsoleta* and *P. ravida* males, the length of the antennal club represent almost one fourth of the body length (Table 1). This is evident in the antennae

observed only in males lamellae, randomly distributed on IN of DL (Figure 5C).

Table 2).

rod shaped (Figure 5F, Table 2).

center, appearing only on IN of male PL (Figure 5F, Table 2).

**8. Analysis between species - sexual dimorphism** 

(Coleoptera: Scarabaeoidea: Melolonthidae) 29

**Figure 5.** Sensilla on the antennae of male *Phyllophaga opaca*. A) External surface (EX) of proximal lamella (PL). Detail of placodea sensilla (PLAS) type III, basiconica sensilla (BAS) type II and III. B) Coeloconica sensilla (COS) type I, BAS I and BAS IV on internal surface (IN) of distal lamella (DL). C) Detail of auricilica sensilla (AUS) type I and II, COS I and PLAS VIII on IN of PL. D) PLAS II, PLAS III, AUS II and BAS II on IN of medium lamella (ML). E) Detail of AUS III on IN of PL. F) COS I, COS III, BAS IV and BAS V on IN of PL. Micrographies by T. Laez.

or elliptical and thin-walled plates (Figures 4D-5D, Table 2). PLAS type III are located on both sides of all lamellae, principally on pit and peripheral edges in both sexes; they are small, elliptical, thin-walled plates or low dome-shaped plates (Figures 4B-5A, Table 2). PLAS type VIII are chemoreceptors not reported previously; they are spherical or elliptical and thin-walled plates with "human-ear" like structure in the center. PLAS VIII were observed only in males lamellae, randomly distributed on IN of DL (Figure 5C).

28 Sexual Dimorphism

**Figure 5.** Sensilla on the antennae of male *Phyllophaga opaca*. A) External surface (EX) of proximal lamella (PL). Detail of placodea sensilla (PLAS) type III, basiconica sensilla (BAS) type II and III. B) Coeloconica sensilla (COS) type I, BAS I and BAS IV on internal surface (IN) of distal lamella (DL). C) Detail of auricilica sensilla (AUS) type I and II, COS I and PLAS VIII on IN of PL. D) PLAS II, PLAS III, AUS II and BAS II on IN of medium lamella (ML). E) Detail of AUS III on IN of PL. F) COS I, COS III,

BAS IV and BAS V on IN of PL. Micrographies by T. Laez.

AUS type I were observed randomly distributed on IN of all lamellae for both sexes; they are characterized by a "rabbit-ear" shape or elliptical and thin-walled plates (Figures 4C-5C, Table 2). AUS type II were observed only in male lamellae, distributed on IN of ML and DL; they are "rabbit-ear" shaped structures, elliptical and low dome-shaped (Figures 5C-D, Table 2). AUS type III were located only on male lamellae, randomly distributed on IN of lamella center (except on the IN of DL); they are characterized by a "human-ear" shape (Figures 5E, Table 2). AUS type IV were restricted to the center of PL in both sexes; their shape is characterized as "rabbit-ear with neck" or "raisin with neck" structures (Figure 4F, Table 2).

BAS type I were observed randomly distributed mostly on IN of all club lamellae of both sexes (except on peripheral edges and on the external surface of ML); they are large peg- or cone-shaped (Figures 4E-5B, Table 2). BAS type II are short-spine shaped; for both sexes, they are situated on both sides of all lamellae (Figure 5D, Table 2). BAS type III were observed for both sexes distributed on both sides of all lamellae; they are short-cone shaped (Figures 4F-5A, Table 2). BAS type IV were found randomly distributed on IN of all club lamellae of both sexes of PL and DL; they are serrated-cone shaped (Figures 4C-5B-5F, Table 2). BAS type V were found only in males, mainly at the center of the IN of PL; they are longrod shaped (Figure 5F, Table 2).

For both sexes, COS type I are restricted principally to the center, appearing only at the IN of all club lamellae. They are found as aggregations of 2 to 16 long peg- or cone-shaped structures (BAS I) located inside depressions or cavities in the antennal cuticle (Figures 4 and 5, Table 2). COS type II were found as aggregations of two to three serrated coneshaped structures (BAS IV) located on the floor of cuticle cavities. These cavities vary in size between 11.58 and 17.54 μm on the largest axis. COS type III are restricted principally to the center, appearing only on IN of male PL (Figure 5F, Table 2).
