Chinese Journal of Entomology (1995) 15, 239-255

Chain-Ing T. Shih and Sheuan-Ping Shiue (1995)
Copulation competition of male Tetranychus urticae Koch and Tetranychus kanzawai Kishida (Acarina: Tetranychidae) with conspecific and heterospecific females and their isolation mechanism
Chinese Journal of Entomology 15 (3), 239-255
Abstract: More than 9,6.7% of male Tetranychus urticae Koch (TSM) and Tetranychus kanzawai Kishida (KSM) copulated with conspecific or heterospecific females (CF or HF) in 30 min of pairing. The rates of second matings of CF and HF with TSM males were 66.7% and 69.0%, respectively, and 36.7% and 13.3 % with KSM males, respectively. The rate of second matings of KSM females with conspecific males was lower than that of TSM females. With precopulation guarding, KSM males guarded a teleiochrysalis at the detention position-the first guarding status. KSM males exhibited a higher tendency than TSM males to mate first with a guarded female upon her emergence, where at the coguarding position the male generally got a second mating chance in sequence with the female. The first guarding males gave up their guarding status to mate first with intruding females and then immediately resumed the first guarding status - mate-first strategy. Conesquently, KSM, performed better in population competition than TSM when both populations existed in the same ecological habitat because of a higher tendency to perform precopulation guarding, the mate-first strategy and second mating.
Under conditions with the presence of females of both species, the males first and second copulation rates with CF or HF were not significantly different (Chi² = 1.914, df=1). The copulated females produced a 10.3 % -13.6 % non-insemination rate which revealed that these two spider mites retain a control mechanism on the sex ratio in their populations. During heterospecific pairing and female guarding, 80% of KSM males were interrupted and 75% were replaced by heterospecific rival males, while 81% and 100 % of TSM males were interrupted and replaced, respectively. With conspecific pairing and female guarding, males were interrupted and replaced by a conspecific rival male 57 % and 24 % of the time for TSM and 73 % and 18 % for KSM, respectively; 13.3 % of once-mated females mated again with their coguarding males. TSM and KSM males did not show any preference of mating choice between CF or HF, and conspecific rival males interrupted conspecific mating pairs at a low rate (20~23 %) and their replacment rate was lower than that of heterospecific mating pairs. Consequently, there must be intraspecific communication and affinity mechanisms existing in both TSM and KSM, and the evidence of high interruption and replacment rates in heterospecific pairing by conspecific males also reveals a behavioral isolation mechanism. existing between TSM and KSM. The KSM males competed with and excluded the TSM population by wasting mating chances, times and energy of TSM females.
Durations of the first mating between a TSM male and a CF or a HF lasted 199 and 116 sec, while those of a KSM male lasted 156 and 80 sec, respectively. No males of a conspecific mating pair were replaced by a rival male. Although a short interuption might have occurred, the males immediately resumed a second part of copulation which was much shorter than the initial part. Female spider mites during heterospecific pairing exhibited escaping, idiosoma lowering, body turning and hitting, and facing the males to prevent the male from entering the copulation position, while during conspecific pairing females did perform any one of these behaviors but conformed to the males movements and approaches. Copulation durations between heterospecific TSM and KSM varied from 31~235 sec. The amount of sperm transferred during conspecific copulation was positively correlated with copulation duration in TSM but not in KSM, where a 30 sec copulation duration was enough for female insemination. Relationships between male ages and female insemination rates need further study. The morphological studies of seminal receptacles on con- and heterospecific-copulated females, showed no heterospecific sperm transfer from male to female. Consequently, isolation mechanisms between TSM and KSM would probably not include mating plug, genetic incompatibility between sperm and ovum, rejection of sperm from seminal receptacle, or antagonistic reactions against the heterospecific sperm in the receptacle and/or during the sperm migration in the hapmocoel, but should be due to physical differences or un-suitability between the aedeague and the receptacle, or due to the omission of one or more chemical or pheromonal cues which induce the male to transfer sperm.
(The abstract is excluded from the Creative Commons licence and has been copied with permission by the publisher.)

Research topic(s) for pests/diseases/weeds:
general biology - morphology - evolution

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Tetranychus urticae
	Tetranychus kanzawai