The 28-spotted potato ladybird beetle is an endemicspecies of the Russian Far East. Nowadays the potato ladybird beetle is widespread across Primorsky and Khabarovsky kray, south Sakhalin, Kunashir Island, and in China, Japan, and India. This paper presents historical data on the dispersal of the potato ladybird beetle in Russia. The first records of the pest presence in the coastal area of Primorsky kray were made in 1929. In the 1950s and 1960s, the pest was observed to inhabit not only the forest steppe zone and the districts adjacent to the taiga in Primorsky kray, but also Khabarovsky kray, Amur oblast and Jewish autonomous oblast. The process of dispersal of the potato ladybird beetle can be divided in several stages: the formation of a new breeding ground, an increase in the size of the pest population, the dispersal of the pest. The range expansion of the potato ladybird beetle can be linked to two facts. First, the land area under potato cultivation increased and neared the breeding grounds of the pest. Secondly, thedietary preference of the phytophagous insect shifted to the new fodder plant. In addition, the development of transportation routes played an important role in the dispersal of the pest. Therefore, anthropogenic factors significantly affected the distribution of the potato ladybird beetle. These factors in combination with a high ecological plasticity of the pest allowed the phytophagous insect to spread across the whole area under potato cultivation in the south of the Russian Far East.

The 28-spotted potato ladybird beetle belongs to the subfamily Epilachninae, which is comprised exclusively by phytophagous insects. The potato ladybird beetle is a dangerous pest of potato in the south of the Russian Far East. Besides potato, it causes damage to tomatoes, cucumbers, watermelons, marrows and eggplants. Adult beetles and larvae eat the parenchyma of leaves severely damaging them. As the result, leaves turn yellow and wither. One beetle can eat up to 15 cm2 of leave surface on average per day, and 300-700 cm2 over its lifetime. A larva can eat from 20 to 30 cm2 of leave surface while developing. This significantly reduces the yield. The body of an adult beetle is small (males, 4-6 mm; female, 5-7 mm), dome-shaped, and elliptical. The elytra are yellow or brownish with 28 black round spots. Some spots, especially the ones along the line of junction, can partially merge. The color of the underside of male beetles is lighter than in females. Male beetles have yellow or less frequently darkened prothorax, mesothorax and metathorax, epimera, and the uppermost edge of the sternites of the abdomen. The anal sternite of the abdomen has a curve with two depressions. The underside of a female beetle is black. The uppermost edge of the anal sternite is straight and with a flat depression. The body of a larva is greyish, oval and with numerous setae. There are 4 rows of black chitinous spinules on the back. Depending on an instar, larvae have a different number of projections on the chitinous spinules. Pupae are exarate, light yellow, and have larval skin remnants at the apex of the abdomen. There are two large black spots on the backside of the thoracic segments. The spots on the abdominal segments are smaller. Fairly long protruding setae grow sparsely on the bodies of pupae. Eggs of the potato ladybird beetle are yellow, elongated, with a pointed apex and a flat bottom. The surface of an egg is characterized by a fine cellular structure.

Relevance. Population dynamics (population waves) is an intrinsic quality of population systems. These fluctuations can be induced by various factors, e.g. environmental conditions and resource availability, elements of a food chain from the same or a higher level (competitors, parasites, predators), and diseases. Few researchers have addressed the issue of the population dynamics of Henosepilachna vigintioctomaculata in the Russian Far East. This paper investigates the reasons why the potato ladybird beetle became a pest of introduced cultivated plants.Materials and methods. To collect data on imagines, all research sites were examined at intervals of eight days during the entire period of the study. The examination of the research sites was conducted within one day. All the imagines taken from host plants were marked at the first encounter by puncturing their elytra with a sewing needle (0.4 mm in diameter) according to Hirano. The next generation of beetles was marked with nail polish (in two-three days after emergence) to avoid traumatizing the insects. At the second encounter, these beetles were also marked by puncturing their elytra with a needle. The methods implemented did not have an adverse effect on the survivability of the studied imagines. The beetles were released to the same plants where they had been taken from. The research data were analyzed by Jolly’s method.Results. Overwintered imagines appeared in the fields and began ovipositing at the end of May. The first generation of imagines appeared at the end of June – the begging of July. The second generation of imagines could be observed at the end of July – the beginning of August. A part of the imagines migrated to overwintering sites without ovipositing approximately at the end of August. The overwintered beetles were observed to emerge on the Mongolian oak Q uercus mongolica, the greater celandine Chelidonium majus, and the bird cherry Prunus padus. A typical primary biotope of the potato ladybird beetle was a potato field at the stage of vegetative growth (5-7 leaves) surrounded by the couch grass Elymus repens, the common dandelion Taraxacum officinale, and the perennial sow-thistle Sonchus arvensis. Marking the overwintered and new generations of imagines showed that the presence of the potato ladybird beetle in an ecosystem depended on agricultural and agrometeorological conditions.

The 28-spotted potato ladybird beetle Henosepilachna vigintioctomaculata is an endemic pest of field crops in the Russian Far East. The study on the morphotypic structure of a population of this phytophagous insect can facilitate the monitoring of processes occurring in ecosystems. It might contribute to the research on the endemic fauna of the Russian Far East and reveal how varieties form resistance to pesticides. To study the polymorphism and structure of a potato ladybird beetle population, an analysis of elytral color patterns was conducted. The following features were considered: the size and shape of spots, the intensity of color, the position of spots on the elytra relative to the elytral suture, the presence of merged spots. As the result, nine morphotypes were identified. The morphotype A2 was the most frequent (47.81 %) and followed by the morphotypes A1 and A6. The morphotype A9 had the lowest frequency of occurrence (1.82 %). It was also determined that morphotypes differed in the linear dimension of spots on the elytra. The form A2 was characterized by the largest spots. The size of the color patterns varied from 104.98 ± 0.071 to 297.01 ± 0.065 µ. The form A1 had the smallest spots.

Relevance. The 28-spotted potato ladybird beetle, Henosepilachna vigintioctomaculata, causes severe damage to plants of the Solanaceae family in the south of the Russian Far East. Today the application of chemicals is the main method for protecting crops against the potato ladybird beetle. This leads not only to the eradication of the pest, but also to the pollution of agricultural ecosystems and the emergence of potato ladybird beetle populations that are resistant to pesticides. A study on the seasonal cycles of the development of the potato ladybird beetle may help to devise new methods for controlling this pest.Methods. We conducted laboratory experiments to study the developmental timing ofa potato ladybird beetlepopulation. The number of eggs was counted, and then the eggs were placed in Petri dishes. The number of emerged larvae was recorded on a daily basis. The hatched larvae were transferred to glass containers (hereafter rearing cages) in batches of 10. We recorded the dates of the transition from one immature developmental stage to another notingthe simultaneity of these transitions. At the onset of the pupal stage, the date was recorded and food was withdrawn from the rearing cages. Scientific observations were carried out on the emergence ofyoung beetles. Field research on the phenology of the potato ladybird beetle was conducted at afield site of 40 m2. The timing of the following events was recorded: the emergence of the adult beetles from diapause, the colonization of the potato field, the beginning and the end of oviposition, the emergence of the larvae and the pupae, the flight of the new insect generation.Results and conclusion. Our laboratory experiment on the immature developmental stages of the potato ladybird beetle revealed that the egg stage was 4-5 days in duration, the larval stage was 16-17 days and the pupal stage was 4-5 daysunder optimal conditions. We also observed deviations from the mean values, which could be conditioned by external factors. For instance, the duration of embryonic development depended either on humidity or on the time range of hatching from one egg mass. The observed deviations of the developmental timing of the larvae and the pupae were most probably due to the quantity and quality of the available food, and the presence of secondary metabolites and glycoalkaloids in it. The field research on thephenology of the potato ladybird beetle showed that there was only one generation in 2020, but two generations in 2021. After comparing climatic conditions in 2020 and 2021, we concluded that Henosepilachna vigintioctomaculata can produce two generations during dry and hot years.