Micro-evolution in the weevil genus Larinus: the formation of host biotypes and speciation

Data are presented on allozyme variation between 15 populations of the stenophagous capitulum weevil, Larinus cynarae , and three populations of its congener, L. latus , that had been collected throughout the northern mediterranean range of these species. A phenetic analysis of these data revealed no direct relationship between genetic variation and host-plant association within L. cynarae , but there was a strong geographical structuring of allozyme patterns. Most of the genetic variation was due to differences between geographical regions and variation within these was small. Wright's F _ST values showed that Italian and Greek populations of L. cynarae were most distinct from L. latus , with southern Iberian, northern Spanish and French populations increasingly less so. This pattern was associated with a cline in the frequencies of certain alleles along this geographical arc from France to Greece. A phenogram of Nei's genetic distances indicated the close genetic relationship between the two species of Larinus and separated the populations of L. cynarae into three allopatric groups. These groups have different host-plant spectra - dominated by Cynara cardunculus in Italy and Greece, Cynara humilis/Onopordum in southern Iberia and Onopordum spp. in France/Northern Spain - and can be considered to be host biotypes of L. cynarae. L. latus , which occurs in Greece and further east is also an Onopordum specialist. An analysis of the phylogeny of this group of Larinus indicates a primary separation into eastern ( L. latus ) and western ( L. cynarae ) taxa, with further branching of the L. cynarae lineage into the putative host-biotypes. An hypothesis for the evolution of these taxa is given, based on the evolutionary history of host-plant taxa and geographical constraints.     

Role of visual cues and interaction with host odour during the host-finding behaviour of the cabbage moth

The approach and landing responses of female Mamestra brassicae (L.) (Lepidoptera: Noctuidae) to visual cues from artificial plant leaves of different shapes and presence/absence of cabbage plant odour were investigated in a laboratory wind tunnel. The leaves were painted with cadmium yellow colour and observed under dim red light. Females showed oriented flight towards plant odours but landed significantly more often when the odour was presented with an artificial leaf. In three-choice tests, the shape of the leaf targets (circle, square or triangle) did not influence the female response. However, the size of the target did influence the insect response: the females preferred landing on square targets with sides of 5 or 10 cm rather than on the largest target, with sides of 15 cm. The orientation of the target influenced the insects' response: females landed significantly more often on the target positioned vertically than horizontally.     

Experimental comparison of anthropophily between geographically dispersed populations of Lutzomyia whitmani (Diptera: Psychodidae)

Lutzomyia whitmani, a major vector of cutaneous leishmaniasis in Brazil, occupies diverse habitats from the Amazon forest canopy to suburban animal pens. Three mitochondrial lineages of Lu. whitmani ('Amazonian', 'North-South' and 'North-east') have parapatric distributions coinciding with different ecological zones. We assessed the host preferences of populations representing the three lineages in standardized field experiments, and found that Lu. whitmani in all sites were significantly more attracted to humans than to dogs or chickens. Females from a southerly population of the North-South lineage showed the greatest degree of anthropophily. Lu. whitmani from Amazonia were also strongly attracted to human baits, contradicting previously published accounts. Intraspecific comparisons in non-Amazonian sites suggest that Lu. whitmani is less anthropophilic than Lu. intermedia but more so than Lu. longipalpis. No significant difference was detected in anthropophily between Lu. whitmani in the Amazon and either Lu. dendrophyla or Lu. gomezi. Anthropophilic behaviour was demonstrated in the same site for Lu. complexa, Lu. flaviscutellata and Lu. brachyphalla, but not for Lu. infraspinosa.