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

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

of several melolonthid species, in which males have longer antennae than females [18,10,34,35]. Furthermore, sexual differences in antennal length are mostly evident in the lamellar club, which is the most important sensorial zone for pheromone and allelochemical perception for these insects [23]. Because *P. obsoleta*, *P. ravida* and *P. opaca* males have longer antennae, longer and wider lamellae, and greater antennal area, males can be regarded as the receptors in their sexual chemical communication [25]. Previous studies with these species have provided morphological and biological evidence that females display a calling behavior during which they expose the protractile genital chamber from the abdominal tip and release chemical compounds that are attractive to males [36,25].

Sexual Dimorphism in Antennae of Mexican Species of *Phyllophaga* 

lamellae of other species have a maximum of six sensilla types [27,23,35]. For Coleoptera in general, only thirteen types of sensilla have been reported in three different Carabidae species [37]. Previous studies for others species use terminology and classification based largely on [21] and [31]; these papers report the main sensilla types as PLAS, BAS, and COS [34,38], including the AUS [27,23]. Part of the results obtained in *P. opaca* clearly show a distinct sexual dimorphism principally with PLAS VIII and COS III, observed only in males. The data obtained at the time allow viewing two main perspectives to continue with studies of this type: data useful in taxonomy and data that allow relating the morphology of the sensilla with the sexual behaviour of the Mexican species of *Phyllophaga*. On the one hand, we found evidence that the types of antennal receptors could be support some subgroups into the studied genus. For example, the main types of chemo-sensilla were presented in both *P. ravida* and *P. opaca* studied: PLAS I, PLAS II, PLAS III, AUS I, AUS II, AUS III, AUS IV, BAS I, BAS II, BAS III, COS I and COS III (Table 3), which belong to the subgenus

*Phyllophaga obsoleta, P. ravida* and *P. opaca* belongs to three of the groups of Mexican species proposed by [18,30]. During forcoming years we expect to study representative species of most of the remaining 38 groups, their sexual dimorphism, phocused on antennal micromorphology, genital structure, production of chemical attractans and reproductive behavior.

A. Aragón (BUAP) helped with collection of specimens of *P. ravida* and G. Lugo (UAS) with collection of specimens of *P. opaca*. A special thanks to J. Valdez (COLPOS) and T. Laez (INECOL) with scanning electron microscope images. A.A.R.L. is grateful to INECOL for

[1] Crowson RA. The biology of the Coleoptera. Academic Press: London 802 p; 1981. [2] Lawrence JF. Order Coleoptera. In: Stehr FW (ed.) Immature Insects vol. 2. Kendall

[3] Beutel RG, Leschen RAB. Morphology and systematics (Archostemata, Adephaga, Myxophaga, Polyphaga partim). Coleoptera, Beetles Vol. 1. Walter de Gruyter: Berlin

*Escuela de Biología, Benemérita Universidad Autonóma de Puebla, Puebla, Mexico* 

*Instituto de Ecología, Xalapa, Veracruz, Apartado postal 63, Mexico* 

financial support during his postdoctoral stay.

/Hunt Publishing Co. Dubuque: 1991. p144-658.

*Phyllophaga*.

**Author details** 

Miguel Angel Morón

**Acknowledgement** 

**9. References** 

567 p; 2005.

Angel Alonso Romero-López

(Coleoptera: Scarabaeoidea: Melolonthidae) 31

In *P. opaca*, the size and proportions of antennae of male is nearly similar as in female, so may be hypothesised that olphactory sensilla works in different form or that sexual attractant is distinct. Functional olphactory antennal surface (club lamellar area) in male of *P. opaca* is two times smaller than in the antennae of *P. ravida*, and 1.5 times smaller than in the antennae of *P. obsoleta* (Table 1).

The morphological study for *P. opaca* receptors is the second for melolonthids with several different types of antennal sensilla (after the *P. ravida* record). In similar studies, antennal


PLAS= sensilla placodea; AUS= sensilla auricilica; BAS= sensilla basiconica; COS= sensilla coeloconica;

TRS= sensilla trichodea; CHS= sensilla chaetica.

PLAS, AUS, BAS and COS are present on internal surface of lamellae while TRS and CHS are structures that occurs along the peripheral edges of each lamella and some are in the lamellar center.

*POBS: Phyllophaga obsoleta* 

*PRAV: Phyllophaga ravida* 

*POP: Phyllophaga opaca* 

**Table 3.** Comparison of the different sensilla types of the lamellae of females and males of *Phyllophaga obsoleta, Phyllophaga ravida and Phyllophaga opaca.*

lamellae of other species have a maximum of six sensilla types [27,23,35]. For Coleoptera in general, only thirteen types of sensilla have been reported in three different Carabidae species [37]. Previous studies for others species use terminology and classification based largely on [21] and [31]; these papers report the main sensilla types as PLAS, BAS, and COS [34,38], including the AUS [27,23]. Part of the results obtained in *P. opaca* clearly show a distinct sexual dimorphism principally with PLAS VIII and COS III, observed only in males. The data obtained at the time allow viewing two main perspectives to continue with studies of this type: data useful in taxonomy and data that allow relating the morphology of the sensilla with the sexual behaviour of the Mexican species of *Phyllophaga*. On the one hand, we found evidence that the types of antennal receptors could be support some subgroups into the studied genus. For example, the main types of chemo-sensilla were presented in both *P. ravida* and *P. opaca* studied: PLAS I, PLAS II, PLAS III, AUS I, AUS II, AUS III, AUS IV, BAS I, BAS II, BAS III, COS I and COS III (Table 3), which belong to the subgenus *Phyllophaga*.

*Phyllophaga obsoleta, P. ravida* and *P. opaca* belongs to three of the groups of Mexican species proposed by [18,30]. During forcoming years we expect to study representative species of most of the remaining 38 groups, their sexual dimorphism, phocused on antennal micromorphology, genital structure, production of chemical attractans and reproductive behavior.
