Alexey Polilov

Lomonosov Moscow State University | MSU · Department of Entomology

Miniaturization leads to considerable reorganization of structures in insects, affecting almost all organs and tissues. In the smallest insects, comparable in size to unicellular organisms, modifications arise not only at the level of organs, but also at the cellular level. Miniaturization is accompanied by allometric changes in many organ systems....

This book addresses microinsects, their structure and their differences from larger relatives. Moreover, it discusses structural changes that accompany extreme diminution in living organisms, evolutionary inventions that help insects to live in the microworld, and factors that limit the size of animals. It also takes a careful look at the potential...

Flight speed is positively correlated with body size in animals ¹ . However, miniature featherwing beetles can fly at speeds and accelerations of insects three times their size ² . Here we show that this performance results from a reduced wing mass and a previously unknown type of wing-motion cycle. Our experiment combines three-dimensional reconst...

The structure of compound eyes in arthropods has been the subject of many studies revealing important biological principles. However, until recently, these studies were constrained by the two-dimensional nature of available ultrastructural data. Here, by taking advantage of the novel three-dimensional ultrastructural dataset obtained using volume e...

The structure of compound eyes in arthropods has been the subject of many studies revealing important biological principles. However, until recently, these studies were constrained by the two-dimensional nature of available ultrastructural data. Here, by taking advantage of the novel three-dimensional ultrastructural dataset obtained using volume e...

The structure of the central nervous system (CNS) of Habrobracon hebetor Say 1836 during the development from prepupa to imago was studied using histological methods and three-dimensional computer modeling. The metamorphosis of the CNS in H. hebetor largely coincides with the previously described changes in related groups of Hymenoptera. During dev...

Microinsects are capable of associative learning and memory retention despite significant reduction in the number and size of neurons. Previously, the capabilities of Thrips tabaci (Thysanoptera, Thripidae) for associative learning and the formation of short-term memory have been demonstrated. In this study, an additional training session was added...

The structure of compound eyes in arthropods has been the subject of many studies revealing important biological principles. However, until recently, these studies were constrained by the two-dimensional nature of available ultrastructural data. Here, by taking advantage of the novel three-dimensional ultrastructural dataset obtained using volume e...

The size of image volumes in connectomics studies now reaches terabyte and often petabyte scales with a great diversity of appearance due to different sample preparation procedures. However, manual annotation of neuronal structures (e.g., synapses) in these huge image volumes is time-consuming, leading to limited labeled training data often smaller...

Body size is the major factor to the flight mechanics in animals. To fly at low Reynolds numbers, miniature insects have adaptations in kinematics and wing structure. Many microinsects have bristled wings, which reduce inertia and power requirements when providing good aerodynamic efficiency. But both bristled and membranous-winged microinsects fly...

Miniaturization is an evolutionary trend observed in many animals. Some arachnid groups, such as spiders and mites, demonstrate a strong tendency toward miniaturization. Some of the most miniaturized spiders belong to the family Anapidae. In this study, using light and confocal microscopy and 3D modelling, we provide the first detailed description...

Methods of three-dimensional electron microscopy have been actively developed recently and open up great opportunities for morphological work. This approach is especially useful for studying microinsects, since it is possible to obtain complete series of high-resolution sections of a whole insect. Studies on the genus Megaphragma are especially imp...

In the course of evolution, animals and particularly insects, have developed efficient and complex mechanisms for survival. Biomimetics aims to find applications for these features of organisms (or organs) in industry, agriculture, and medicine. One of these features is the thin, flexible, and mobile insect ovipositor, which is also capable of carr...

Anucleate animal cells are a peculiar evolutionary phenomenon and a useful model for studying cellular mechanisms. Anucleate neurons were recently found in one genus of miniature parasitic wasps of the family Trichogrammatidae, but it remained unclear how widespread this phenomenon is among other insects or even among different tissues of the same...

Miniaturization constrains insects with the task of preserving vital body functions in spite of significant reductions in body size. The effects of miniaturization on the functioning of the insect nervous system were investigated in the parasitoid Trichogramma telengai. Despite a decreased number of neurons and their volume, T. telengai demonstrate...

An Erratum to this paper has been published: https://doi.org/10.1134/S1607672955340036

The size of image stacks in connectomics studies now reaches the terabyte and often petabyte scales with a great diversity of appearance across brain regions and samples. However, manual annotation of neural structures, e.g., synapses, is time-consuming, which leads to limited training data often smaller than 0.001\% of the test data in size. Domai...

Miniaturization is one of the important trends in the evolution of terrestrial arthropods. In order to study adaptations to microscopic sizes, the anatomy of the smallest insects was previously studied, but not the anatomy of the smallest mites. Some of the smallest mites are Eriophyidae. In this study we describe for the first time the anatomy of...

Insect antennae are astonishingly versatile and have multiple sensory modalities. Audition, detection of airflow, and graviception are combined in the antennal chordotonal organs. The miniaturization of these complex multisensory organs has never been investigated. Here we present a comprehensive study of the structure and scaling of the antennal c...

Holometabolan brains undergo structural and allometric changes and complex reorganizations during metamorphosis. In minute egg parasitoids, brain formation is shifted to the late larva and young pupa, due to extreme de-embryonization. The brains of Megaphragma wasps undergo denucleation, the details of which remained unknown. We describe the morpho...

The structure of the brain of the smallest coleopteran, Scydosella musawasensis Hall, 1999, is described for the first time. As in other extremely small beetles, the brain of S. musawasensis displays signs of miniaturization: displacement to the thorax, compactization, and a small number and size of the neurons. The body size of the studied smalles...

Megaphragma species are important models for basic organismal research, and many are potential biological control agents. We present the first extensive revision of species of the genus Megaphragma based on morphological and molecular data. Our revision includes all previously described species, 6 of which are synonymized, and 22 of which are descr...

Built for speed. The cover shows the feather-like wings of the tiny beetle Paratuposa placentis. How fast an animal can fly is usually dictated by its size: the larger the animal, the faster it flies. But at just 395 micrometres big, P. placentis bucks this trend by flying as fast as insects three times its size.

As the study of the human brain is complicated by its sheer scale, complexity, and impracticality of invasive experiments, neuroscience research has long relied on model organisms. The brains of macaque, mouse, zebrafish, fruit fly, nematode, and others have yielded many secrets that advanced our understanding of the human brain. Here, we propose t...

Extreme miniaturization implies a high degree of optimization, rendering the retention of non-functional organs almost impossible. Two unique non-porous placoid sensilla on the antennae of females of Megaphragma were described in the literature. Placoid sensilla in Hymenoptera have an olfactory function and always bear pores; the apparent absence o...

Flight speed generally correlates positively with animal body size [1]. Surprisingly, miniature featherwing beetles can fly at speeds and accelerations of insects three times as large [2]. We show here that this performance results from a previously unknown type of wing motion. Our experiment combines three-dimensional reconstructions of morphology...

Modern morphological and structural studies are coming to a new level by incorporating the latest methods of three-dimensional electron microscopy (3D-EM). One of the key problems for the wide usage of these methods is posed by difficulties with sample preparation, since the methods work poorly with heterogeneous (consisting of tissues different in...

During metamorphosis, the insect CNS undergoes both structural and allometric changes. Due to their extreme de-embryonization and parasitism, the formation of the CNS in egg parasitoids occurs at the late larval stage. Our study provides the first data on the morphological and volumetric changes of the CNS occurring during the pupal development of...

Revealing scaling rules is necessary for understanding the morphology, physiology and evolution of living systems. Studies of animal brains have revealed both general patterns, such as Haller's rule, and patterns specific for certain animal taxa. However, large-scale studies aimed at studying the ratio of the entire neuropil and the cell body rind...

Miniaturization is a major evolutionary trend prominent in insects, which has resulted in the existence of insects comparable in size to some unicellular protists. The adaptation of the complex antennal multisensory systems to extreme miniaturization is a fascinating problem, which remains almost unexplored. We studied the antennal sensilla of Scyd...

Miniaturization strongly affects functional morphology. Whereas some anatomical structures are barely affected by scaling, others can fundamentally change as the body becomes ever smaller. No prior study has focused on the effect of miniaturization on grooming and attachment structures in Hymenoptera, which can be highly diverse and complex. Throug...

Most microinsects have feather-like bristled wings, a state known as ptiloptery, but featherwing beetles (family ptiliidae) are unique among winged microinsects in their ability to fold such wings. An asymmetrical wing folding pattern, found also in the phylogenetically related rove beetles (Staphylinidae), was ancestral for ptiliidae. Using scanni...

Size is a key to locomotion. In insects, miniaturization leads to fundamental changes in wing structure and kinematics, making the study of flight in the smallest species important for basic biology and physics, and, potentially, for applied disciplines. However, the flight efficiency of miniature insects has never been studied, and their speed and...

Aerodynamic force generation capacity of the wing of a miniature beetle Paratuposa placentis is evaluated using a combined experimental and numerical approach. The wing has a peculiar shape reminiscent of a bird feather, often found in the smallest insects. Aerodynamic force coefficients are determined from a dynamically scaled force measurement ex...

Acoustic communication plays an important role in the life of insects and especially in representatives of the order Orthoptera. Their vibrational signalling, unlike signalling by sound, is poorly studied. The pygmy grasshoppers Tetrix tenuicornis (Sahlberg, 1891) belonging to the ancestral family Tetrigidae (Orthoptera) can produce several types o...

Body size reduction, also known as miniaturization, is an important evolutionary process that affects a number of physiological and phenotypic traits and helps animals conquer new ecological niches. However, this process is poorly understood at the molecular level. Here, we report genomic and transcriptomic features of arguably the smallest known i...

Smaller animals display pecular characteristics related to their small body size, and miniaturization has recently been intensely studied in insects, but not in other arthropods. Collembola, or springtails, are abundant soil microarthropods and form one of the four basal groups of hexapods. Many of them are notably smaller than 1 mm long, which mak...

A view of the outer chiasm and first optic neuropil of the Megaphragma amalphitanum visual system. Skeletal reconstructions of photoreceptor axons and lamina monopolar neurons corresponding to 18 optical facets (ommatidia). This tiny wasp only has 29 ommatidia in each of its compound eyes compared to the ~750 found in that of Drosophila. Neuron r...

Body size reduction, also known as miniaturization, is an important evolutionary process that affects a number of physiological and phenotypic traits and helps animals to conquer new ecological niches. However, this process is poorly understood at the molecular level. Here, we report genomic and transcriptomic features of arguably the smallest know...

Pterothoracic structures of the minute ptiliid Nephanes titan were examined and described in detail. Effects of miniaturization and the phylogenetic and functional background are discussed. Apomorphies shared with Hydraenidae are the large metascutal shield, the fringe of setae along the posterior edge of the wings, and the fusion of the mesoventri...

The coleopteran family Ptiliidae (featherwing beetles) includes some of the smallest insects known with most of the representatives of this family measuring less than 1 mm in body length. A small body size largely determines the morphology, physiology, and biology of an organism and affects the organization of complex sense organs. Information on t...

The wings of Ptiliidae, the coleopteran family containing the smallest free-living insects, are analyzed in detail for the first time. A reconstruction of the evolutionary sequence of changes associated with miniaturization is proposed. The wings of several species are described using light microscopy and scanning electron microscopy. The morpholog...

The smallest beetles and the smallest non-parasitic insects belong to the staphylinoid family Ptiliidae. Their adult body length can be as small as 0.325 mm and is generally smaller than 1 mm. Here we address the phylogenetic relationships within the family using formal analyses of adult morphological characters and molecular data, and also a combi...

ScienceDirect Illustration on front cover: One of the smallest insects, the featherwing beetle Nephanes titan (Coleoptera: Ptiliidae) is shown in an eye of a needle in an SEM micrograph taken by A.A. Polilov.

One of the major trends in the evolution of parasitoid wasps is miniaturization, which has produced the smallest known insects. Megaphragma spp. (Hymenoptera: Trichogrammatidae) are smaller than some unicellular organisms, with an adult body length of the smallest only 170 µm. Their parasitoid lifestyle depends on retention of a high level of senso...

Revealing the effect of brain size on the cognitive abilities of animals is a major challenge in the study of brain evolution. Analysis of the effects of miniaturization on brain function in the smallest insects is especially important, as they are comparable in body size to some unicellular organisms and next to nothing is known about their cognit...

Myxophaga are a small group of beetles, but phylogenetically crucial as one of the four coleopteran suborders. The monogeneric Sphaeriusidae, one of four myxophagan families, comprise about 20 species, most of them living in moist substrate at river edges. The morphology of the minute hemispherical adult is very insufficiently known. Consequently,...

Here is the first description of the visual organ of Acrotrichis grandicollis, a member of Ptiliidae family that includes the smallest free-living insects. The apposition eyes of A. grandicollis have the acone-type crystalline cone; a fused rhabdom is formed by eight retinula cells and surrounded by primary pigment cells. Secondary pigment cells ar...

Ptiliidae include the smallest known beetles. External and internal head structures of species with different body sizes and feeding preferences were examined and described in detail. Saprophagous and sporophagous species are compared. The observed features are evaluated with respect to their phylogenetic and functional significance, and their corr...

Megaphragma is recorded for the first time in Columbia where it is represented by M. caribea that emerged from leaves of Terminalia catappa infested by the thrips (Heliothrips haemorrhoidalis and Selenothrips rubrocinctus). M. caribea has anucleate neurons, the third species of Megaphragma shown to have this feature.

Miniaturization is an evolutionary process that is widely represented in both invertebrates and vertebrates. Miniaturization frequently affects not only the size of the organism and its constituent cells, but also changes the genome structure and functioning. The structure of the main heat shock genes (hsp70 and hsp83) was studied in one of the sma...

Miniaturization is an evolutionary process that is widely represented in both invertebrates and vertebrates. Miniaturization frequently affects not only the size of the organism and its constituent cells, but also changes the genome structure and functioning. The structure of the main heat shock genes (hsp70 and hsp83) was studied in one of the sma...

The third communication in this series describes the structure of the brain in one of the smallest psocopterans, Liposcelis bostrychophila (Liposcelididae), studied in a series of histological sections with the use of 3D reconstructions and TEM. Like all microinsects, L. bostrychophila shows both oligomerization and concentration of ganglia, an inc...

This article describes the morphology and ultrastructure of the brain of the greenhouse thrips, Heliothrips haemorrhoidalis (Thripidae), studied in a series of histological sections with the use of 3D reconstructions and TEM. The structural peculiarities of the brain organization and its features associated with body miniaturization as well as its...

The body size, especially in cases of extreme reduction, is an important characteristic that strongly determines the morphology, physiology, and biology of animals. Miniaturization is a widespread trend in animal evolution and one of the principal directions of evolution in insects. Miniaturization-related features of insect morphology have been su...

Internal morphology of Megaphragma mymaripenne, 3D. (A, B) Intestine and Malpighian tubules; (C, D) Central nervous system; (A, C) Dorsal view; (B, D) Lateral view; ag–abdominal ganglion, cer–cerebrum, gg1.2.3 –pro-, meso-, and metathoracic ganglia, mg–midgut, mt–Malpighian tubules, oes–oesophagus, rc–rectum, soeg–suboesophageal ganglion. (PDF)

Reproductive system of Megaphragma mymaripenne, 3D. (A, B) Female; (C, D) Male; (A, C) Lateral view; (B, D) Dorsal view; acg–acid gland, aed–aedeagus, agl–accessory glands, alg–alkaline gland, ova–ovary, spt–spermatheca, stl–stylet of ovipositor, te–testis, val–valves of ovipositor. (PDF)

Supplementary references. (PDF)

Interactive animated 3D reconstruction of the Megaphragma mymaripenne for Fig 5. Click on the figure to start interactive 3D view. Colors: blue–cuticle, green–digestive system, yellow–central nervous system, brown–musculature, purple–reproductive system. (PDF)

Internal structure of Megaphragma mymaripenne. (A) Scheme of sections, lateral view; (B–E) Longitudinal sections, toluidine blue, pyronine; acg–acid gland, ag–abdominal ganglion, cer–cerebrum, fr2 –mesophragma, gg1,2,3 –pro-, meso-, and metathoracic ganglion, mg–midgut, mt–Malpighian tubules, oc–eye, ova–ovary, rc–rectum. Musculature see text. (PDF...

Homology of head musculature in Hymenoptera. (PDF)

Musculature of adult Chalcidoidea and Ichneumonoidea. (PDF)

Homology of musculature of mesosoma in Hymenoptera. (PDF)

Over millions of years of evolution, the genomes of modern insects have accumulated a significant num­ ber of mutations, which often can lead up a blind alley when carrying out phylogenetic research. Genomic differences between some representatives belonging to the same family or group are often so great that they demand using nonconventional metho...