**Author details**

30 Sexual Dimorphism

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

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 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

**Sensilla types** *POBS PRAV POP*  **PLAS I** X X X **PLAS II** X X X **PLAS III** X X X **AUS I** X X X **AUS II** X X X **AUS III** X X **AUS IV** X X **BAS I** X X X **BAS II** X X X **BAS III** X X X

**COS I** X X X

**COS III** X X

**TRS** X X X **CHS** X X X

PLAS, AUS, BAS and COS are present on internal surface of lamellae while TRS and CHS are structures that occurs

**Table 3.** Comparison of the different sensilla types of the lamellae of females and males of *Phyllophaga* 

and release chemical compounds that are attractive to males [36,25].

**BAS IV** X **BAS V** X

**COS II** X

**COS IV** X

along the peripheral edges of each lamella and some are in the lamellar center.

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

the antennae of *P. obsoleta* (Table 1).

TRS= sensilla trichodea; CHS= sensilla chaetica.

*obsoleta, Phyllophaga ravida and Phyllophaga opaca.*

*POBS: Phyllophaga obsoleta PRAV: Phyllophaga ravida POP: Phyllophaga opaca* 

Angel Alonso Romero-López *Escuela de Biología, Benemérita Universidad Autonóma de Puebla, Puebla, Mexico* 

Miguel Angel Morón *Instituto de Ecología, Xalapa, Veracruz, Apartado postal 63, Mexico* 
