Negative covariance between larval Arrenurus sp. and Limnochares americana (Acari: Hydrachnidia) on male Leucorrhinia frigida (Odonata: Libellulidae) and its relationship to the host's age

Numbers of larval Arrenurus sp. and Limnochares americana Lundblad mites, parasitic on adult males in a population of Leucorrhinia frigida Hagen, were found to be negatively correlated. The two mite species did differ in their seasonality, but a strong negative covariance remained even when analyses were run separately on data grouped by day. When dragonflies were separated into tenerals and sexually mature males, almost all newly emerged males were heavily parasitized by Arrenurus sp. and rarely parasitized by L. americana, whereas males holding reproductive territories were almost always heavily parasitized by L. americana but carried reduced loads of Arrenurus sp. When territorial males were subdivided dependent on presence or absence of Arrenurus sp., the dragonflies with Arrenurus were significantly less heavily parasitized than those without Arrenurus sp. Through the above partitioning of data, plus recapture of previously marked dragonflies, it was established that the negative covariance between mite taxa reflects the differences in host discovery: Arrenurus sp. attaches to dragonflies during the host's emergence from the water, whereas L. americana attaches to males while they defend reproductive territories at the water's margin. We conclude that the age-correlated differences in infestation of dragonflies by mites could be a valuable method for determining relative age within odonate populations.

Territorial behaviour of male Nannothemis bella (Uhler) (Anisoptera: Libellulidae)

Male Nannothemis bella (Uhler) dragonflies are territorial at the breeding site. On the basis of the male behavioural time budgets, the species can be regarded as a territorial percher. Those acts involved in territorial maintenance (patrolling and fighting) are more closely related to territorial dimensions than are those not concerned with the territory (feeding). Territoriality appears closely related to some aspect of the water area within a territory, as maintenance and defence behaviour vary most consistently with the size of this area. Territorial size increases as the season progresses. Defensive behaviour is directed at both conspecifics and a heterospecific, Leucorrhinia frigida. The usefulness of a marking technique for dragonflies was tested statistically.

CHROMOSOME NUMBERS OF SOME NORTH AMERICAN DRAGONFLIES (ODONATA)

Chromosome numbers for 111 species of North American Odonata are reported. In five species, Enallagma cyathigerum (Charp.), Ophiogomphus bison Sclys, Dorocordulia iibera (Selys), Epitheca cynosura (Say), and Leucorrhinia frigida Hagen, primary spermatocytes from single individuals had different chromosome numbers. This is presumed to arise from either fusion or "splitting" of chromosomes. Fusion in D. libera, E. cynosura and L. frigida results in reduction of chromosome number, and "splitting" in E. cyathigerum and O. bison gives higher chromosome numbers.The idea that high chromosome numbers in Odonata are primitive is rejected. An alternative hypothesis is proposed: that low numbers are primitive (or secondarily derived) and high numbers advanced.