Laboratory of Insect Diapause
Diapause is a central element of insect life-cycle. Diapause allows insects to overcome harsh seasons and exploit fluctuating resources. Diapause phenotype includes photoperiodism, hormonal regulation, cessation of development, altered gene expression, cell cycle arrest, accumulation of energy reserves, metabolic suppression, and bolstered environmental stress tolerance. We focus on basic research of seasonally acquired cold hardiness (metabolic switching to accumulation of cryoprotective compounds, restructuring of membrane composition, adjustments of membrane function, expression of chaperons and other protective proteins). Our results may serve practical purposes: development of new techniques for cryopreservation of biological material; forecasting the seasonal activities and estimation of overwintering survival in populations of pest species.
Survival in liquid nitrogen
The goal is to reveal biochemical and molecular mechanisms that allow diapausing larvae of drosophilid fly, Chymomyza costata to survive deep freezing and long-term cryopreservation in liquid nitrogen. Knowledge on principles of such extreme cold hardiness can serve as a basis for development of cryopreservation techniques for insects or other biological material. We believe that the extreme freeze tolerance of C. costata larvae is based on synergy of different mechanisms and, therefore, chose wide integrative approach including: (1) studies on how diapause, cold and drought acclimations alter metabolic pathways in larval tissues toward production and accumulation of innate cryoprotective mixture including amino acids, sugars, and other components. We are interested in how the cryoprotective mixture components affect dynamism of internal ice formation, stabilize proteins and protect them from loss of structure and activity, and protect the integrity of biological membranes; (2) analysis of adaptive changes in lipid composition of biological membranes, which affect the membrane fluidity and phase behavior and, consequently, allow maintaining barrier function at extremely low temperatures and upon freeze-dehydration; (3) search in C. costata genome for putative macromolecular cryoprotectants including heat shock proteins, ice binding proteins, and dehydration induced LEA-like proteins. We follow expression of their genes during acclimations, localize the protein products in tissues, and study their cryoprotective functions using artificial proteins produced in expression vectors.
Insect overwintering as limiting factor for poleward spread
Insects have successfully colonized almost all terrestrial ecosystems and this success is closely associated with their remarkable adaptations to endure climatic extremes. Even so, insect distributions are currently changing rapidly in response to climate change. The project address questions related to the physiological limits and/or drivers of insects' poleward colonization of colder habitats from tropical hotspots. We focus on overwintering stage of insect life cycle in select models (e.g. adults of linden bug, Pyrrhocoris apterus) and ask what exactly the environmental factors are that limit the winter survival of their populations. In addition to the apparent and often considered low temperature extremes, we study the effects of microhabitat temperature buffering, moisture and risk of ice nucleation, repeated bouts of freezing and melting, ice recrystallization, warm spells that may cause cold de-acclimation and energy depletion on one side, but repair of chronic cold injury on the other side. In addition to analyzing select insect species in detail, we exploit the family of drosophilid flies that offers ideal model system of more than 1 500 species (many of them readily available and easy to maintain in laboratory) that represent the evolutionary journey from original tropical-African habitats to the species which are now firmly established in sub-Arctic regions. We analyze metabolic responses in different species to various levels of cold stress ranging from brief cold shock and short-term quiescence to long-term acclimation including diapause induction and exposure to subzero temperatures to find whether there are any stereotypic metabolic patterns (e.g. accumulation of typical osmolytes) that would underlie the capacity of species to tolerate the cold stress and, consequently, to colonize the colder habitats.
Overwintering in insects of economic importance
We follow the course and the success of overwintering in insect pest species (or beneficial insects) in their field habitats. We assess the seasonal timings of diapause induction, initiation, termination and the onset of spring activity. We assess a whole set of physiological parameters, which correlate and/or are causally involved in cold tolerance and winter mortality. We use various techniques (supercooling point, vapour pressure and Clifton nanoliter osmometers, differential scanning calorimetry, gas exchange and respirometry analysis, high resolution mass spectrometry, etc.). Select target species: Ips typographus, Pityogenes chalcographus, Cydia pomonella, Ostrinia nubilalis, Culex pipines and others.