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Antipredator strategies of the pupal stage in insects have received little attention in comparison to larval or adult stages. This is despite the fact that predation risk can be high during the pupal stage, making it a critical stage for subsequent fitness. The immobile pupae are not, however, defenceless; a wide range of antipredator strategies have evolved against invertebrate and vertebrate predators. The most common strategy seems to be ‘avoiding encounters with predators' by actively hiding in vegetation and soil or via cryptic coloration and masquerade. Pupae have also evolved behavioural and secondary defences such as defensive toxins, physical defences or deimatic movements and sounds. Interestingly, warning coloration used to advertise unprofitability has evolved very rarely, even though the pupal stage often contains defensive toxins in chemically defended species. In some species, pupae gain protection from conspecifics or mimic chemical and auditory signals and thereby manipulate other species to protect them. Our literature survey highlights the importance of studying selection pressures across an individual's life stages to predict how ontogenetic variation in selective environments shapes individual fitness and population dynamics in insects. Finally, we also suggest interesting avenues for future research to pursue. This article is part of the theme issue ‘The evolution of complete metamorphosis’.

The applicability of spectral analysis in detection of freshwater metal contamination was assessed by developing and testing a novel hyperspectral imaging (HSI) application for aquatic insect larvae (Trichoptera: Hydropsychidae). Larvae were first exposed to four different cadmium (Cd) concentrations: 0, 1, 10, and 100 μg L−1 for 96 h. Individual larvae were then preserved in ethanol, inspected with microscopy for the number of anomalies in larval gills, and imaged by hyperspectral camera operating with wavebands between 500 and 850 nm. Three additional larvae from each exposure were analyzed for tissue Cd concentration. Although the larval tissue Cd concentrations correlated positively with actual water concentrations, the toxicity response of larvae, i.e., frequency of gill abnormalities, did not differ among the Cd concentrations. In contrast, hyperspectral imaging data indicated some concentration-response relationship of larval spectral properties to the Cd exposure, but it was too weak for reliable automatic distinction between exposed and unexposed larvae. In this pilot study a workflow for data processing for a novel application of hyperspectral imaging was developed. Based on the results of this preliminary study, the workflow in the imaging process will be optimized and its potential for detecting metal contamination of aquatic environments reassessed. peerReviewed

Diet is one of the major factors directly and indirectly influencing insect’s life history traits and risk of getting infected. Additionally the insect’s fitness is severely affected by the broad diversity of parasites they are exposed to. As a consequence insects have developed well-evolved defences. Behavioural responses include self-medication, the ability of insects to change dietary intake in response to an infection. When studying this ability it is of major importance to consider the insects natural diet range. In this thesis I investigated the effect of different host plants on fitness and immunocompetence of polyphagous Arctia plantaginis larvae and whether the larvae can therapeutically and prophylactically self-medicate by optimising their diet intake. Additionally I examined the long-term effect of prophylactic treatment on lab-reared larvae from the same species. Feeding experiments reveal that the host plants plantain (high in biologically active compounds) and dandelion (high nutritional value) have different effect on the larval development and survival. Results show that a monotonous plantain diet provides lowest protection against an infection, whereas a diet switch from plantain to dandelion increases survival. Immunocompetence seems to be not differently affected by the two host plants. When given the choice, all larvae choose to ingest a mixture of both plants. The ratio of both plants differed depending on the infection status or infection risk in their environment compared to control larvae. This highlights the importance of a mixed diet for some polyphagous species and that dietary variety should be considered when studying insects’ ability to therapeutically and prophylactically medicate. A prophylactic medication applied to laboratory- reared insects showed negative effects on life-history traits and reproductive success, and thus should be carefully considered. In conclusion these findings provide insights in the crucial importance of diet mixing for polyphagous larvae and show evidence for the larvae ability to therapeutically and prophylactically medicate by mixing their diet.

Anthropogenic climate change and habitat loss and deterioration affect populations worldwide. Climate warming has changed phenologies of many species across trophic levels. Some predator populations now experience temporal mismatches with their prey, as timings of peak prey abundance and of the predator’s highest food demands no longer meet. The temporal mismatch hypothesis suggests that the population’s recruitment rate is related to its degree of synchrony with the food resources needed to feed offspring. However, species’ and populations’ responses to climate warming differ. Human land use alters and destroys habitats of countless species. For example, many boreal forest bird populations have declined, presumably due to intensive forestry. It has decreased the amount of dead wood, causing a threat to saproxylic species. Identification of the key characteristics of high-quality habitats is essential for conservation planning and for developing sustainable forestry. As individuals are suspected to settle in habitats that maximize their fitness, analysis of nest site selection can be used to identify the key habitats. My dissertation concerns the impacts of climate change and habitat deterioration on boreal populations. I use hole-nesting passerines as model species. By utilizing long-term data I show that breeding phenologies of Parus major and Poecile montanus, but not of Cyanistes caeruleus, have shifted earlier. Also, the timing of the food peak has advanced, improving the synchrony between P. montanus and caterpillars. In P. major and C. caeruleus, synchrony has remained good. However, the positive effect of good synchrony on breeding success seems to be conditional, arising only in certain circumstances, such as in years of high caterpillar abundance. I suggest that in boreal populations temperature affects timing of breeding mostly as a proximate factor. The availability of standing decaying trees used for nesting sites was the most important habitat characteristic determining the nest site selection of P. montanus. Remote sensing data alone was insufficient to produce reliable models, as the ecologically important small-scale factor can only be determined by direct field surveys. Omission of forest thinning in selected forest sites would ensure the continuous availability of decaying wood with positive influence on biodiversity in managed forests. Tiivistelmä Ihmisen aiheuttama habitaattien katoaminen ja huononeminen sekä ilmastonmuutos vaikuttavat populaatioihin kaikkialla maailmassa. Ilmaston lämpeneminen on muuttanut monien lajien fenologioita eri trofiatasoilla. Osalla saalistajalajien populaatioista suurin ravinnontarve ei enää ajoitu samaan aikaan saaliin runsaushuipun kanssa. Ajoituksen eriaikaisuus -hypoteesin mukaan todennäköisyys populaatioon rekrytoitumiselle riippuu synkronian asteesta saaliin kanssa. Ilmaston lämpenemisen vaikutuksissa lajeihin ja populaatioihin on kuitenkin vaihtelua. Ihmisen maankäyttö muuttaa ja tuhoaa lukuisien lajien elinympäristöjä. Esimerkiksi useiden boreaalisten metsien lintupopulaatioiden pienentymistä on selitetty intensiivisellä metsätaloudella. Lahopuun määrä metsissä on vähentynyt, mikä on uhka lahopuusta riippuvaisille lajeille. Korkealaatuisten habitaattien keskeisten piirteiden tunnistaminen on tärkeää luonnonsuojelun ja kestävän metsätalouden suunnittelulle. Koska yksilöiden oletetaan valitsevan niiden kelpoisuutta maksimoivia elinympäristöjä, pesäpaikanvalinta-analyysiä voidaan käyttää tärkeiden habitaattipiirteiden tunnistamiseen. Tarkastelen väitöskirjassani ilmastonmuutoksen ja habitaattien laadun vaikutuksia boreaalisiin populaatioihin. Mallilajeina käytän koloissa pesiviä varpuslintuja. Hyödyntämällä pitkäaikaisaineistoja osoitan, että lisääntymisen ajoittuminen on aikaistunut tali- ja hömötiaisella, mutta ei sinitiaisella. Myös ravintohuippu on aikaistunut, mikä on parantanut synkroniaa hömötiaisen ja sen pääasiallisen ravinnon eli toukkien välillä. Tali- ja sinitiaisella synkronia on pysynyt hyvänä. Hyvän synkronian myönteinen vaikutus lisääntymismenestykseen vaikuttaa kuitenkin ehdolliselta: se tulee esiin vain tietyissä olosuhteissa, kuten vuosina jolloin toukkia on runsaasti. Kevään lämpötilat näyttävät vaikuttavan pesinnän ajoittumiseen erityisesti proksimaattisena tekijänä. Pesäpaikkoina toimivien seisovien lahopuiden määrä on tärkein hömötiaisen pesäpaikanvalintaa määräävä tekijä. Kaukokartoitusaineisto yksinään ei riitä luotettavien mallien tuottamiseen, sillä ekologisesti tärkeät pienen skaalan tekijät voidaan kartoittaa vain suorin maastomittauksin. Metsien harventamatta jättäminen valituilla laikuilla turvaisi lahopuun jatkuvan saatavuuden, mikä vaikuttaisi myönteisesti talousmetsien biodiversiteettiin.

Suppealla alueella esiintyvät päiväperhoslajit ovat usein paikallisesti suhteellisen runsaslukuisia. Tämän yllättävän seikan havaitsi filosofian maisteri Jussi Päivinen tutkiessaan väitöskirjaansa varten päiväperhosia. Havainto on maailmanlaajuisesti erittäin harvinainen. Yhtenä syynä voi olla Suomen pohjoinen sijainti, jonka seurauksena monien päiväperhoslajien levinneisyysalue rajoittuu Etelä-Suomeen. - Levinneisyysalueensa reunalla elävät perhoslajit pystyvät asuttamaan ainoastaan suurimmat ja laadultaan parhaimmat elinympäristölaikut, mutta koska laikut ovat korkealaatuisia, niihin voi muodostua erittäin runsaslukuiset päiväperhoskannat. Reuna-alueella elävien päiväperhosten ns. elinympäristölaikut ovat todennäköisesti eristyneempiä kuin niiden lajien, joiden levinneisyysalue kattaa suuren osan tutkittavasta alueesta, Päivinen selvittää. Several mechanisms have been proposed to explain the patterns of species richness, distribution and abundance. Also several mechanisms have been put forward in explaining the generally observed positive relationship between regional distribution and local abundance of species. In this thesis factors affecting distribution, abundance and species richness were studied using butterflies and myrmecophilous beetles as study objects. The data of myrmecophilous beetles are based on the literature and a field survey and data of butterflies is based on the literature. This thesis suggests that ant colonies maintain species rich beetle fauna, and that widespread host ant species and the species with large colony size are able to maintain higher species richness of myrmecophilous beetles. Surprisingly, a strong negative relationship between local abundance and regional distribution was found for the Finnish butterflies. The study suggested that sedentary butterfly species, species at the edge of their distribution range and the most specialized species were locally abundant with restricted distribution. Mobile species, species furthest from the edge of their distribution and generalist butterfly species were locally few in number and widespread, thus, generating the negative relationship. Larval specificity, habitat breadth and resource availability were observed to be in a key role when explaining the mobility of the butterflies. Range position had strong effect both on the mobility and on the length of the flight period of the butterflies. The surprising results emphasize the importance of the study of basic ecology of species. More studies are needed to find out, whether observed negative relationship between distribution and abundance is a more general phenomenon than previously thought.

Assimilation of cow liver by Lucilia illustris (Meigen) larvae was studied in the laboratory. The larvae were cultured from hatching to the end of development in the respiration chambers of an infra-red gas analyser (IRGA), and respiration was measured as CO2 production. Assimilation was calculated in both carbon and energy units. In this organism the Cr203 indicator method proved unsuitable for measuring food consumption. In early larval development respiration showed two linear phases, which are suggested to be correlated with the first two instars. Both the cumulative and the instantaneous net production efficiency, K2 (production/assimilation), were calculated. Integration of the latter to the final larval weight produced results similar to those obtained by direct determination. K2 varied both with temperature and with the developmental stage of the larvae (weight). Efficiency was highest during the most intense growth phase, or a little before it, then being 88 % in carbon units (90 % in energy units) at 25 to 300C. At this optimal temperature the cumulative K2 to the end of the feeding period was 82 % (84 %); in changing temperature conditions the corresponding K2 was 77 0 (79 %). The value of instantaneous concepts in bioenergetic research and the application of IRGA to measurements of animal respiration is discussed.