Spatial structuring in trait variation in Polyommatus icarus in a functional context

The Common blue butterfly, Polyommatus icarus (Rott,) , is widespread throughout its Palaearctic distribution and persists in areas with differing climatic conditions. It is known to be a highly variable butterfly with marked within and between population variation in morphology, thermal biology, and voltinism. These traits together with allozymes and a neutral DNA marker (AFLP) variation are studied here to understand how geographic trait variation is related to environmental variation. The approach adopted here is to study this along a latitudinal cline of temperature and photoperiod, using four populations from south to north within mainland Britain. AFLP differences, but not allozyme variation, indicate genetic structuring, with an isolation by distance effect. Enzyme diversity of P. icarus butterflies in the British Isles is lower than on mainland Europe, indicative of a past bottleneck. This, combined with selection on, or drift in, the allozymes could cause for a lack of population structure in this marker. Despite high levels of gene flow between populations, local adaptation is possible, as differentiation in certain allozyme loci was found (PGM and PGI). Populations differed in their response to developmental cues. Northern populations have an obligate diapause strategy and southern populations' development times differ in response to temperature, indicating local variation in response to environmental conditions. Populations differed in wing morphology (size, shape and melanisation) but this was not related to latitude. Experimental determination of heating rates in different basking positions and thoracic temperature at take-off revealed no strong relationships of the morphological characteristics with heating or cooling rates and an indication of relationship with PGI alleles. It is suggested that m comparison to larger butterflies morphological variation IS unconstrained by thermal requirements. The persistence and widespread occurrence of this butterfly may be a consequence of the variability of traits within this butterfly

Why small is beautiful: wing colour is free from thermoregulatory constraint in the small lycaenid butterfly, Polyommatus icarus

We examined the roles of wing melanisation, weight, and basking posture in thermoregulation in Polyommatus Icarus, a phenotypically variable and protandrous member of the diverse Polyommatinae (Lycaenidae). Under controlled experimental conditions, approximating to marginal environmental conditions for activity in the field (= infrequent flight, long duration basking periods), warming rates are maximised with fully open wings and maximum body temperatures are dependent on weight. Variation in wing melanisation within and between sexes has no effect on warming rates; males and females which differ in melanisation had similar warming rates. Posture also affected cooling rates, consistent with cooling being dependent on convective heat loss. We hypothesise that for this small sized butterfly, melanisation has little or no effect on thermoregulation. This may be a factor contributing to the diversity of wing colours in the Polyommatinae. Because of the importance of size for thermoregulation in this small butterfly, requirements for attaining a suitable size to confer thermal stability in adults may also be a factor influencing larval feeding rates, development time and patterns of voltinism. Our findings indicate that commonly accepted views of the importance of melanisation, posture and size to thermoregulation, developed using medium and large sized butterflies, are not necessarily applicable to small sized butterflies

Insecticidal effects of deltamethrin in laboratory and field populations of Culicoides species: how effective are host-contact reduction methods in India?

BACKGROUND: Bluetongue virus (BTV) is transmitted by Culicoides biting midges and causes bluetongue (BT), a clinical disease observed primarily in sheep. BT has a detrimental effect on subsistence farmers in India, where hyperendemic outbreaks impact on smallholdings in the southern states of the country. In this study, we establish a reliable method for testing the toxic effects of deltamethrin on Culicoides and then compare deltamethrin with traditional control methods used by farmers in India. RESULTS: Effects of deltamethrin were initially tested using a colonised strain of Culicoides nubeculosus Meigen and a modified World Health Organisation exposure assay. This method was then applied to field populations of Culicoides spp. in India. The field population of C. oxystoma in India had a greater LC50 (0.012 ± 0.009%) for deltamethrin than laboratory-reared C.nubeculosus (0.0013 ± 0.0002%). Exposure of C. nubeculosus to deltamethrin at higher ambient temperatures resulted in greater rates of knockdown but a lower mortality rate at 24 h post-exposure. Behavioural assays with C. nubeculosus in WHO tubes provided evidence for contact irritancy and spatial repellence caused by deltamethrin. The field experiments in India, however, provided no evidence for repellent or toxic effects of deltamethrin. Traditional methods such as the application of neem oil and burning of neem leaves also provided no protection. CONCLUSIONS: Our study demonstrates that field-collected Culicoides in India are less susceptible to deltamethrin exposure than laboratory-bred C. nubeculosus and traditional methods of insect control do not provide protection to sheep. These low levels of susceptibility to deltamethrin have not been recorded before in field populations of Culicoides and suggest resistance to synthetic pyrethrioids. Alternative insect control methods, in addition to vaccination, may be needed to protect Indian livestock from BTV transmission

DNA barcoding and surveillance sampling strategies for Culicoides biting midges (Diptera: Ceratopogonidae) in southern India

Background: Culicoides spp. biting midges transmit bluetongue virus (BTV), the aetiological agent of bluetongue (BT), an economically important disease of ruminants. In southern India, hyperendemic outbreaks of BT exert high cost to subsistence farmers in the region, impacting on sheep production. Effective Culicoides spp. monitoring methods coupled with accurate species identification can accelerate responses for minimising BT outbreaks. Here, we assessed the utility of sampling methods and DNA barcoding for detection and identification of Culicoides spp. in southern India, in order to provide an informed basis for future monitoring of their populations in the region. Methods: Culicoides spp. collected from Tamil Nadu and Karnataka were used to construct a framework for future morphological identification in surveillance, based on sequence comparison of the DNA barcode region of the mitochondrial cytochrome c oxidase I (COI) gene and achieving quality standards defined by the Barcode of Life initiative. Pairwise catches of Culicoides spp. were compared in diversity and abundance between green (570 nm) and ultraviolet (UV) (390 nm) light emitting diode (LED) suction traps at a single site in Chennai, Tamil Nadu over 20 nights of sampling in November 2013. Results: DNA barcode sequences of Culicoides spp. were mostly congruent both with existing DNA barcode data from other countries and with morphological identification of major vector species. However, sequence differences symptomatic of cryptic species diversity were present in some groups which require further investigation. While the diversity of species collected by the UV LED Center for Disease Control (CDC) trap did not significantly vary from that collected by the green LED CDC trap, the UV CDC significantly outperformed the green LED CDC trap with regard to the number of Culicoides individuals collected. Conclusions: Morphological identification of the majority of potential vector species of Culicoides spp. samples within southern India appears relatively robust; however, potential cryptic species diversity was present in some groups requiring further investigation. The UV LED CDC trap is recommended for surveillance of Culicoides in southern India

Comparison of the models for maximum temperature, heating rates and cooling rates for both weight and melanisation.

<p>* Quantitative comparison of the models was done by calculating the F ratio as: F = [(difference in SS explained)/(difference in df)] / (residual mean square of model 1)</p><p>Comparison of the models for maximum temperature, heating rates and cooling rates for both weight and melanisation.</p

Maximum body temperatures (means +/- S.E.) for the three different basking positions (see Fig 1) for male (▀) and female (▲) <i>P</i>. <i>icarus</i> (basking position: F_2,86 = 998.8, P < 0.0001).

<p>Maximum body temperatures (means +/- S.E.) for the three different basking positions (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0122623#pone.0122623.g001" target="_blank">Fig 1</a>) for male (▀) and female (▲) <i>P</i>. <i>icarus</i> (basking position: F_2,86 = 998.8, P < 0.0001).</p

Heating (A) and cooling (B) rates of <i>P</i>. <i>icarus</i> butterflies in three basking positions (means +/- S.E.) (Heating: F_2,86 = 414.15, P < 0.0001; Cooling: F_2,86 = 4.74, P = 0.011).

<p>For basking positions see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0122623#pone.0122623.g001" target="_blank">Fig 1</a>.</p

Frame with <i>Polyommatus icarus</i> male with partially opened wings (basking position 2) used to determine thoracic temperatures during heating and cooling experiments.

<p>The thermoprobe (front) is inserted in the thorax and held in place by a strap (a). Schematic representation of the three basking positions (b).</p