Correlattion Between Flower-visiting Behaviors Of Colocasiomyia Flies And The Flowering Phynology,the Rhythm Of Inflorescence Thermogenesis Of Host Plant

Flies of the genus Colocasiomyia(Diptera: Drosophilidae)were distributed in the tropical and subtropical regions.Most Colocasiomyia species visit and breed obligatory on inflorescences/infructescences of Araceae host plants.They served as specific pollinators of the host plants,and rely on the host inflorescences/infructescences through almost their whole life cycle.adults feed and mate on the inflorescences,and larvae grow(and sometimes pupate)in the inflorescences the Aroid host plants.Some Colocasiomyia species evolved intimate pollination mutualism with their host plants,thus serve as ideal system for study of mutualism evolution.In this study,the flower-visiting behaviors of Colocasiomyia flies and their correlation with the flowering phenology,the rhythm of inflorescence thermogenesis of the host plant,Rhaphidophora decursiva,is investigated.Based on field observation of flowering phenology of the host plant and the behaviors of Colocasiomyia flies,the observed phenological period was divided into three major sections: sections I corresponds to inflorescence bud before anthesis;section II coresponding to anthesis and was subdivided into five stages: stages I(the day of anthesis starting)and II(the second day of anthesis)corresponding to the female(stigma receptivity)phase,stages III(the third days,with pollen start to present),IV(roughly the fourth to fifth days,with extensive pollen presentation)and V(roughly the fifth to sixth days,anther withered and fallen off)corresponding to the male(anther dehiscence)phase;section III coresponding to the starting of fruiting.Similar as previously reported,exact synchrony was observed between the flower-visiting behaviors of Colocasiomyia flies and the phenology of R.decursiva.The thermogenesis of R.decursiva inflorescence proved to be obviously rhythmical,with nearly same thermogenesis pattern(in either rhythm or temperature)detected among the distal,medial and proximal sections of the inflorescences,which is attributable to the fundamental floral traits,i.e.,bisexual floret and spatially unzonated inflorescence of the subfamily Monsteroidean compared to that of the subfamily Aroideae.Three heat production were observed,all occurred before noon.The first and second ones occurred during the female phase(stages I and II),the third one occurred during the male phase,and exhibit maximal temperature difference between inflorescences and the ambience.Based on our phylogenical observation,these heat productions were presumed to be in favor of the follwoing processes,respectively: synthesis/emission of the volatile olfactory compounds(VOCS),the pollen germination/pollen tube growth,and the growth of stamens/dehiscence of anther dehiscence/release of pollens.Our investigation revealed that spathe is the major feeding substrate for the larvae of the summar generation of C.hailini on R.decursiva.Comparison between the two generations of this C.hailini species revealed strong morphological and behavioral adaptation of this species to its host plants.Taking into account also the above-mentioned results,the precise phenological synchrony between the Colocasiomyia flies and their Monsteroidean host plants indicates well evolution of intimate pollination mutualism in this interaction system.