Impact of cold on the immune system of burying beetle, Nicrophorus vespilloides (Coleoptera: Silphidae)

Abstract

Insect overwintering is one of the most astonishing phases of the insect life cycle. Despite vast amounts of knowledge available about the physiological mechanisms of this phenomenon, the impact of stress factors on insect immune system functioning during the winter is still unknown. The aim of this study is to analyze how low temperatures influence the immune system of the beetle Nicrophorus vespilloides. The results show that the beetle's immune system is differently modulated by cold induced in laboratory settings than that which occurs in natural conditions. Among beetles cultured in conditions similar to summer, low temperatures, did not influence the number of circulating haemocytes, phenoloxidase activity, haemocytes morphology, and percentage ratio of haemocyte types. In these beetles, differences were noted only in the ability of haemocytes to perform phagocytosis. Individuals acclimated in natural conditions in autumn had a higher level of humoral response and a different percentage ratio of haemocyte types. During the winter period, the number of haemocytes in the beetles decreased, but the percentage ratio of phagocytic haemocytes increased. Furthermore, we noted an increase of phenoloxidase activity. Our study also showed mitotic divisions of haemocytes in haemolymph collected from burying beetles after cold exposure and from burying beetles collected from natural conditions during autumn and winter. Differences in response to low temperatures in laboratory conditions and the natural environment suggest that the simultaneous presence of other stress factors during winter such as desiccation and starvation have a significant influence on the activity of burying beetle's immune system.

Myotropic activity and immunolocalization of selected neuropeptides of the burying beetle Nicrophorus vespilloides (Coleoptera: Silphidae)

“…Nicrophorus vespilloides beetles were cultured at the Department of Animal Physiology and Development, Faculty of Biology AMU, according to a method previously described by Urbański et al (2014Urbański et al ( , 2017 under stable conditions similar to conditions characteristic of summer in northern Poland (21°C, 15 h light : 9 h dark). The beetles were kept in separate plastic containers and were fed meat twice a week.…”

Characterization of Gromphadorhina coquereliana hemolymph under cold stress

“…The two most numerous types of hemocytes were plasmatocytes and granulocytes. The first group is the predominant group in most insects, as was observed for example in beetles Carabus lefebvrei 55 , N. vespilloides 47 and the fly Simulium vittatum 72 . In turn, the latter group, granulocytes, participate in basic mechanisms of cellular response and in hemolymph clotting, wound healing and necrotic cell phagocytosis 70 , 73 – 75 .…”

“…Yi and Lee 67 showed that the number of hemocytes in Eurosta solidaginis was reduced by 40% under extremely low temperatures (− 80 °C), which in turn decreased the activity of the cellular response. In Coccus hesperidum, cold stress leads to a decrease in the encapsulation ratio 68 , whereas in Nicrophorus vespilloides, cold stress causes a gradual decrease in the number of circulating hemocytes during winter 47 . Additionally, it was shown that cold stress decreases the number of phagocytic cells in diapausing pupae of Samia cynthia pryeri 69 .…”

“…The main components of insect hemolymph are morphotic components—hemocytes 46 . Hemocytes are the primary elements of insects’ immune cellular response and are responsible for the processes of phagocytosis, nodulation, and encapsulation 47 , 48 . Pathogen recognition by hemocytes is also crucial for the activation of the second type of insect immune response, the humoral response, which involves processes in which antimicrobial peptides (AMPs), lysozyme or phenoloxidase (PO) are engaged 49 .…”

The physiological role of fat body and muscle tissues in response to cold stress in the tropical cockroach Gromphadorhina coquereliana

“…Moreover, cold stress can lead to changes in immune system activity. Some immune system variables that can be affected by cold in the burring beetle Nicrophorus vespilloides include total haemocyte count, phenoloxidase activity, and the phagocytic ability of haemocytes [ 38 , 39 ].…”