Egy tévhitekkel terhes környezetpolitikai probléma tisztázása

Széles körben elterjedt vélekedés a kertészetben és növényvédelemben, hogy a növényeket délben, tűző napon nem szabad locsolni, mert a növényekre tapadt vízcseppek megégethetik a leveleket azáltal, hogy a levél felszínére fókuszálják a napfényt. Hasonló vélemény fordul elő a bőrgyógyászatban és kozmetikában is, miszerint az emberi bőrön megtapadt vízcseppek veszélyt jelentenek napozás közben, mert a bőrre fókuszálják a napfényt. Az erdészeti szakirodalomban is föl-fölbukkan az a hit, hogy a vízcseppek által az elszáradt növényzetre fókuszált napfény erdőtüzet okozhat. A növények felületén ülő vízcseppek fényfókuszálását részleteiben eddig még nem vizsgálták. Hogy pótoljam e hiányt, a napsütötte növényi levelekhez tapadt vízcseppek által fókuszált napfény miatti esetleges levélégés mélyebb megértésének céljából négy kísérletet végeztem. Először demonstráltam, hogy vízszintes juharleveleken (Acer platanoides) elhelyezkedő, 1.5 törésmutatójú, 2 és 10 mm közti átmérőjű üveggolyók napsütésben súlyos égési sérüléseket (barnulást) okoznak a levélszövetben. Utána megmutattam, hogy páfrányfenyő (Ginkgo biloba) és korai juhar (Acer platanoides) vízszintes sima, többé-kevésbé víztaszító levelein ülő napsütötte vízcseppek nem képesek beégetni a levélszövetet. Ezáltal megcáfoltam azt a régi közhiedelmet, miszerint eső vagy öntözés után mindig napégést szenvednek a növények a rájuk tapadt vízcseppek napfényfókuszáló hatása miatt. Ugyanakkor azt is megmutattam, hogy napsütésben a rucaöröm (Salvinia natans) erősen víztaszító viaszszőrei által tartott vízcseppek megégethetik a levélszövetet. Vizsgálataim alapján azt a végkövetkeztetést vontam le, hogy azon általános vélekedés, miszerint a növényekhez tapadt vízcseppek apró nagyítólencsékként összegyűjtve a napfényt mindig megégetik a leveleket, nem más, mint egy közkeletű tévhit

Spectral Sensitivity Transition in the Compound Eyes of a Twilight-Swarming Mayfly and Its Visual Ecological Implications

Aquatic insect species that leave the water after larval development, such as mayflies, have to deal with extremely different visual environments in their different life stages. Measuring the spectral sensitivity of the compound eyes of the virgin mayfly (Ephoron virgo) resulted in differences between the sensitivity of adults and larvae. Larvae were primarily green-, while adults were mostly UV-sensitive. The sensitivity of adults and larvae were the same in the UV, but in the green spectral range, adults were 3.3 times less sensitive than larvae. Transmittance spectrum measurements of larval skins covering the eye showed that the removal of exuvium during emergence cannot explain the spectral sensitivity change of the eyes. Taking numerous sky spectra from the literature, the ratio of UV and green photons in the skylight was shown to be maximal for θ ≈ − 13° solar elevation, which is in the θmax = -14.7° and θmin = -7.1° typical range of swarming that was established from webcam images of real swarmings. We suggest that spectral sensitivity of both the larval and adult eyes are adapted to the optical environment of the corresponding life stages.Funding provided by: National Research, Development and Innovation Fund of Hungary*Crossref Funder Registry ID: Award Number: 131738/PD_19Funding provided by: Ministry for Innovation and TechnologyCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100015498Award Number: ÚNKP-21-3Funding provided by: Jan Gershoj*Crossref Funder Registry ID: Award Number

Why do biting horseflies prefer warmer hosts? tabanids can escape easier from warmer targets

Blood-sucking horseflies (tabanids) prefer warmer (sunlit, darker) host animals and generally attack them in sunshine, the reason for which was unknown until now. Recently, it was hypothesized that blood-seeking female tabanids prefer elevated temperatures, because their wing muscles are quicker and their nervous system functions better at a warmer body temperature brought about by warmer microclimate, and thus they can more successfully avoid the host's parasite-repelling reactions by prompt takeoffs. To test this hypothesis, we studied in field experiments the success rate of escape reactions of tabanids that landed on black targets as a function of the target temperature, and measured the surface temperature of differently coloured horses with thermography. We found that the escape success of tabanids decreased with decreasing target temperature, that is escape success is driven by temperature. Our results explain the behaviour of biting horseflies that they prefer warmer hosts against colder ones. Since in sunshine the darker the host the warmer its body surface, our results also explain why horseflies prefer sunlit dark (brown, black) hosts against bright (beige, white) ones, and why these parasites attack their hosts usually in sunshine, rather than under shaded conditions

Method to improve the survival of night-swarming mayflies near bridges in areas of distracting light pollution

Numerous negative ecological effects of urban lighting have been identified during the last decades. In spite of the development of lighting technologies, the detrimental effect of this form of light pollution has not declined. Several insect species are affected including the night-swarming mayflyEphoron virgo: when encountering bridges during their mass swarming, these mayflies often fall victim to artificial lighting. We show a simple method for the conservation of these mayflies exploiting their positive phototaxis. With downstream-facing light-emitting diode beacon lights above two tributaries of the river Danube, we managed to guide egg-laying females to the water and prevent them from perishing outside the river near urban lights. By means of measuring the mayfly outflow from the river as a function of time and the on/off state of the beacons, we showed that the number of mayflies exiting the river's area was practically zero when our beacons were operating. Tributaries could be the sources of mayfly recolonization in case of water quality degradation of large rivers. The protection of mayfly populations in small rivers and safeguarding their aggregation and oviposition sites is therefore important.</jats:p