Phenology of the 28-spotted potato ladybird beetle <i>Henosepilachna vigintioctomaculata</i> in the south of the Russian Far East

Abstract

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 At the onset of the pupal stage, the date was recorded and food was withdrawn from the rearing cages.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.