BR. J. ENT. NAT. HIST., 7: 1994 129 



MCZ 



FACTORS AFFECTING HABITAT PREFJgHRgtfSY 

 IN THE LEPIDOPTERA 



Michael Majerus, Anne-Lisa Grigg, Carys JoNg^fficQjy^/lQSok, 

 Andrew Strathdee and Nicholas Dearnaley 



Department of Genetics, Downing Street, Cambridge, CB2 3EH r}r~\ 



UNIVERSITY 



It is well known that many species of Lepidoptera have specific habitat requirements, 

 and that their geographic distribution, at least in part, reflects the availability of 

 favourable habitats. Habitat favourability may depend on presence of larval or adult 

 food resources, appropriate adult roosting sites, suitable conditions for flight and 

 so on. However, little comparative work has been done to address several questions. 

 Are habitat biases active or passive? Do Lepidoptera actively seek and then stay in 

 favourable habitats, or do those in favourable habitats survive and reproduce while 

 those in other habitats die? What factors affect habitat preferences? How strong may 

 habitat preferences be? 



Results of a single night's light trapping in 1984 suggested that in some species, 

 preferences could be active and strong. Two Heath moth traps, operated 50 yards 

 apart, one in a Douglas fir (Pseudotsuga menziesii (Mirbel)) plantation, the other 

 in mixed deciduous woodland, produced quite different catches. For example, all 

 Hylaea fasciaria were taken in the conifer plantation trap. Conversely, all Diarsia 

 mendica were taken in the deciduous woodland trap. Furthermore, of polymorphic 

 species, such as Semiothisa liturata and Alcis repandata, significant differences were 

 found in the frequencies of forms in the two habitats (Kearns & Majerus, 1987). Other 

 workers have found similar results in respect of a number of polymorphic species 

 (Jones et al, 1993; Aldridge et al., 1993; Fraiers et al., in press). 



Waring (1989) has published results of a more extensive trapping run. During 1984 

 and 1985 he operated Heath traps one night a week in three contrasting woodland 

 habitats in Bernwood Forest; conifer plantation, overgrown coppice broad-leaf and 

 newly coppiced broad-leaf. Taking account of the differences of shading at trap sites, 

 following Bowden (1982), he compared the catches of moths in overgrown coppiced 

 broad-leaf woodland with those in conifer plantation and newly coppiced broad-leaf. 

 Of 50 species of moth taken in sufficient numbers to allow analysis, only one, Aghopis 

 aurantaria was shown to have no significant preference in either comparison for 

 both years. More preferences were for the overgrown coppice than for the more 

 man-managed habitats, but it is interesting to note that for each of the ten species 

 shown to have a preference for conifer plantation, the preference was consistent 

 between years. 



Waring's data transformation, based on Bowden's formula of trapping efficiency 

 being correlated to background illumination, is open to criticism. Recently, Dearnaley 

 et al. (in prep.), have shown that the trapping efficiency of moth traps depends not 

 only on degree of shading, but also on bulb strength, bulb height, trap design and 

 the height of the trap above the ground. However, for many species, Waring's 

 statistical findings are robust, even if the data are not transformed. 



Waring (1989) interprets his results primarily in the light of larval foodplants and 

 adult roosting sites. The habitat preferences shown by many, but not all, species make 

 sense in terms of what is known about these factors. However, microclimatic factors 

 such as temperature, humidity, windspeed etc., which may affect flight, are not 

 considered. This may be because Waring considered that such factors would not differ 

 significantly between his trapping sites, all being in woodland of one sort or another. 



