First report of amitraz and cypermethrin resistance in Rhipicephalus sanguineus sensu lato infesting dogs in Mexico

Engorged female Rhipicephalus sanguineus sensu lato (Ixodida: Ixodidae) were collected from dogs in the state of Yucatán, Mexico. Fourteen tick populations were collected from dogs at seven veterinary clinics, four residential homes and three cattle farms. The larval immersion test was used in the progeny of collected adult females to test susceptibility to amitraz and cypermethrin. Dose–mortality regressions, 50% lethal concentrations (LC₅₀), confidence intervals and slope were estimated by probit analysis. For amitraz, 12 tick populations (85.7%) were classified as resistant and low inter‐population variation in the phenotypic level of resistance was evident [resistance ratios (RRs) at LC₅₀: 1.0–13.0]. For cypermethrin, 12 tick populations (85.7%) were classified as resistant and substantial inter‐population variation in the phenotypic level of resistance was evident (RRs at LC₅₀: 1.0–104.0). Thus, amitraz resistance in R. sanguineus s.l. is common, but generally occurs at low levels; however, alarmingly high levels of cypermethrin resistance are present in R. sanguineus s.l. populations in dogs in Yucatán, Mexico. The intensive use of both acaricides to control ectoparasites on dogs is likely to lead to more serious resistance problems that may cause high levels of control failure in the future.     

Physical barriers and corridors in urban habitats affect colonisation and parasitism rates of a specialist leaf miner

1. Urban environments are fragmented habitats characterised by the presence of physical barriers, which may negatively affect dispersal and colonisation by insect herbivores and their natural enemies. Conversely, plants growing along pavements may function as dispersal corridors, helping to moderate the harmful effects of resource patch isolation on organism movement and population persistence. 2. We experimentally tested the effects of walls as physical barriers to the dispersal of the leaf miner Liriomyza commelinae Frost and colonisation of its host plant, Commelina erecta L., in urban habitats. We also evaluated whether plants along pavements could act as corridors for this species. 3. We exposed experimental host plants to the leaf miner in houses with front gardens and back yards, the latter being completely surrounded by walls. The front gardens had walls but none separating them from the pavement. Previously mined plants were also exposed to parasitoids in the yards to determine parasitoid attack. 4. Liriomyza commelinae took longer to colonise back yards with higher walls, and the abundance of mined plants along pavements reduced the colonisation time. Leaf‐miner abundance was marginally affected by the yard type, and was lower in back yards. Cumulative parasitism rates decreased with increasing distance at which mined plants were placed from pavements. 5. Constructions act as physical barriers, having a negative impact on colonisation of host plants by leaf miners. The function of pavements as corridors seems to depend on the abundance of mined plants. Parasitism may be affected by distance from the corridor rather than physical barriers or other potential hosts.     

Ant body posture: gaster curling increases ant speed

1. Body postures adopted by an animal can serve behavioural functions, homeostasis, or energy balance. 2. We investigated the function of holding the gaster curled forward under the thorax in acacia ants, Pseudomyrmex spinicola Emery, by testing whether ants adopted this posture for defence, thermoregulation, or for efficient locomotion. 3. For the defence hypothesis, we expected an increase in the proportion of ants with curled gasters after a visual threat, a vibrational disturbance of a branch, or the release of nestmate's alarm pheromones. Our data did not support these predictions. 4. For the thermoregulation hypothesis, we found a positive correlation between temperature and proportion of curled‐gaster ants. However, we did not find a reduction in the proportion of curled‐gaster ants after shading them, as predicted by this hypothesis. 5. Our data supported the locomotion hypothesis: curled‐gaster ants walked 1 cm s^?1 faster than ants with the gaster held straight. Straight‐gaster ants walked with the thorax closer to the surface, a posture that likely shifts the centre of gravity closer to the surface in a manner similar to gaster curling. 6. Studying the role of the body posture in acacia ants and other insects will provide a better understanding of the kinematics of walking in challenging angles with respect to gravity.     

The genus Perkinsiana (Polychaeta, Sabellidae) from Antarctica, with descriptions of the new species P. milae and P. borsibrunoi

Perkinsiana antarctica (Kinberg, 1867) and P. littoralis (Hartman, 1967) are redescribed from holo- and topotypes. Two new species, P. milae and P. borsibrunoi , are described from the Ross Sea (Antarctica) and compared with other species of the genus. Records of P. antarctica are numerous, but re-examination indicates that many of these represent misidentifications: the species may have a distribution limited to subantarctic areas.     

RELATIONSHIPS BETWEEN PATELLA FERRUGINEA GMELIN, 1791 AND THE OTHER TYRRHENIAN SPECIES OF PATELLA (GASTROPODA: PATELLIDAE)

The external morphology of soft parts of the rare Patella ferrugineaGmelin, 1791 is described, and its relationships with P. caerulea,P. rustica and P. ulys-siponensis are investigated on both morphologicaland electrophoretic grounds. Soft part morphology is a gooddiscriminative tool, but of little help in detecting affinities.Electrophoretic data on 19 presumptive loci suggest that P.rustica is the closest species to P. ferruginea, whereas P.caerulea and P. ulyssiponensis are clustered separately. Meanobserved heterozyg-osities arc higher in P. ferruginea and P.rustica. It is concluded that in case of subdivision of thegenus Patella L., 1758, P. ferruginea and P. rustica shouldbe placed together in the subgenus Patellastra Mon-terosato,1884. (Received 6 January 1993; accepted 23 February 1993)