Involvement of vitamin A in the photoperiodic induction of diapause in the spider mite Tetranychus urticae is demonstrated by rearing an albino mutant on a semi-synthetic diet with and without p-carotene or vitamin A

Abstract. Data are presented on the development from egg to adult of a wild-type and an albino strain of the spider mite Tetranychus urticae on a semi-synthetic liquid diet.The diet is a modification of the diet developed by Van der Geest et al. (1983).Apart from the standard diet without added carotenoids, diets supplemented with either β-carotene or vitamin A were tested.A high incidence of diapause was found in the wild-type strain under short-day conditions on all three diets.No diapause was found in the albino mutant under short days on the standard diet.Partial restoration of the photoperiodic response was obtained after addition of β-carotene to the diet, and full restoration was found after the addition of vitamin A.Diapause could be terminated in diet-reared diapausing females of both strains after a cold rest of 3 weeks at 4°C.The results lead to the conclusion that vitamin A or a derivative of vitamin A probably functions as the photoreceptor pigment for the photoperiodic induction of diapause in the spider mite.     

Evolutionary Trends of External Morphology in the Marine Mite Genus Rhombognathides (Acari: Halacaridae: Rhombognathinae)

A morphology-based phylogenetic analysis of the eight species of Rhombognathides (Acari: Halacaridae) demonstrated some evolutionary tendencies of character transformation. In the course of the evolution of Rhombognathides, idiosomal plates increased in size or fused. Simple filiform setae transformed into spiniform or bipectinate setae. The number of tarsal claws, the length of median claw and leg chaetotaxy of telofemora and tibiae were reduced. The fusion or expansion of dorsal plates, transformation from filiform to other setal forms, and reduction of leg setae would have recurrently occurred in halacarid evolution. The claw structure most likely reflects adaptation to specific habitat.     

Phoretic and parasitic mites infesting the New World screwworm fly, Cochliomyia hominivorax, following sterile insect releases in Libya

During the screwworm eradication programme in Libya in 1991, trapped specimens of Cochliomyia hominivorax (Coquerel) were found infested with phoretic mites, Macrocheles muscaedomesticae (Scopoli), or parasitic mites, Trichotromidium muscarum (Riley). The possible sources of infestation and potential effects of mites on screwworm flies are discussed.     

Feeding History Affects the Response of the Predatory Mite Typhlodromus Kerkirae (Acari: Phytoseiidae) to Volatiles of Plants Infested with Spider Mites

The response of adult females of the predatory mite Typhlodromus kerkirae (Acari: Phytoseiidae) to volatiles emitted from bean leaves infested with Tetranychus urticae (Acari: Tetranychidae) or from leaves of Oxalis corniculata infested with Petrobia harti (Acari: Tetranychidae) was studied in the laboratory using a Y-tube olfactometer. Typhlodromus kerkirae females reared from larvae through to adults on T. urticae and pollen of Vicia faba responded to volatiles of bean leaves infested with T. urticae, either when they had a choice between infested and non-infested bean leaves or between bean leaves infested with T. urticae and O. corniculata leaves infested with P. harti. However, they did not respond when they had been reared only on the carotenoid-deficient pollen of V. faba. Female T. kerkirae that had been reared from larva to the tenth day of adult life on T. urticae and subsequently fed for 1 week on V. faba pollen did not respond to volatiles of bean leaves infested with T. urticae. In contrast, those that had been reared on V. faba pollen to the tenth day of adult life and subsequently fed for 1 week on T. urticae responded to volatiles of infested bean leaves.     

Comparative trials on the effects of two fungicides on a predatory mite in the laboratory and in the field

Both laboratory tests with the open glass plate method of Louis & Ufer (1995) and a field study in a vineyard were carried out to test the side effects of the two fungicides, Dithane Ultra WG75 and Polyram Combi WG70, on the predatory mite Typhlodromus pyriScheuten (Acarina: Phytoseiidae). The effects of both fungicides in the residual contact test in the laboratory were more pronounced than the actual effects obtained in the field even after multiple application of the test products. The study results suggest, that for the selected test products the current laboratory guidelines correctly triggered the field test. Methodological problems of the laboratory test due to the repellent effect of the fungicides are discussed.     

Competition between mobile species using patchy resources: an example from a freshwater,symbiotic assemblage

Summary Three species of freshwater mites that are symbiotic with mussels in St Mark's River, north Florida, have consistently high rates of colonization to and occupy high proportions of mussels. The mites Unionicola poundsi and U. serrata are territorial and have limited numbers/host, whereas the non-territorial U. abnormipes has highly variable numbers/host. U. abnormipes and U. serrata are most common in Villosa villosa and Uniomerus declivis respectively, patterns that can not be explained by host species preferences, whereas U. poundsi is equally abundant in both host species. Field experiments showed that both U. poundsi and U. serrata were limited most by intraspecific competition between adult mites, presumably for access to food and oviposition sites. Additionally, U. serrata did not remain within small hosts, most of which were V. villosa. In contrast, numbers of U. abnormipes were limited by both other mite species although the nature of the interactions differed. U. serrata may prey on U. abnormipes when they co-occur, whereas U. poundsi probably only excludes U. abnormipes from certain areas within hosts. Hence, U. abnormipes occurs mostly in V. villosa because most of these mussels do not contain U. serrata, but even so its numbers are still depressed by U. poundsi. The results were consistent with the general expectation of Holmes and Price (1986) that parasite assemblages where species have high colonization levels should be organized primarily by biotic interactions. However, specific outcomes of competition between mites were consistent with the more general model of Levins (1979) for competition between species using variable resources. Failure of other models to apply to Unionicola pinpointed at least five key biological characters that may form a better basis of comparison than taxonomic or habitat-based contrasts.     

Effects of fluvalinate on two-spotted spider mite dispersal, fecundity and feeding

Residual deposits of fluvalinate caused two-spotted spider mite,Tetranychus urticae Koch, dispersal by running off (run-off) and spinning down (spin-down) from treated leaves. Run-off occured at concentrations from 0.0005 g a.i. 1⁻¹ and reached a peak at 0.01 g a.i. 1⁻¹. Spin-down was more predominant at concentrations above 0.01 g a.i. 1⁻¹. Spin-down and run-off proportions varied with fluvalinate formulation. Oviposition was temporarily suppressed on fluvalinate-treated leaves, presumably because of an irritant effect which reduced feeding. An emulsifiable concentrate formulation caused the largest reductions in oviposition. Oviposition returned to the level exhibited by untreated mites two days after removal from treated surfaces. Oviposition and feeding were positively correlated and both declined reciprocally with increasing fluvalinate concentration.     

Observations on the mite fauna associated with adult Stomoxys calcitmns in the U.K.

Abstract. Adult females of the blood-sucking muscid Stomoxys calcitrans sampled between June and September 1993 from a cattle farm ( n = 839) and from a pig farm ( n = 542) in North-West England were examined for mites. Twelve species of mites from ten families and three orders were identified as follows. In the Prostigmata, Eryenetes sp., Family Ereynetidae and Pediculaster mesembrinae , Family Pygmephoridae. In the Astigmata, Procalvolia zacheri Family Saproglyphidae, Acarusfarris , Family Acaridae, Bonomoia sphaerocerae and Myianoetus sp., Family Anoetidae. In the Mesostigmata, Macrocheles muscaedomesticae and Macrocheles subbadius Family Macrochelidae, Digamasellus sp., Family Digamasellidae, Halolaelaps sp., Family Halolaelapidae. Prodinychus sp., Family Uropodoidea and Thinoseius sp., Family Eviphididae. Mean infestation rates at the two sites (all mite species) for the entire sampling period were 31.6 ± 13.9% and 19.8 ± 3.6% respectively. 51 % of synbovine flies sampled in July were infested with mites. Mean numbers of flies infested in August at both farms were significantly lower compared to other months. The presence of tritonymphs of Ereynetes sp. on S.calcitrans demonstrates for the first time that this life cycle stage is naturally associated with insects in the field.
All mites were recovered from the ventral thorax and abdomen, and two or more species commonly infested individual flies. Associations of mites with their dipteran hosts are described and discussed.