Lady beetles for biocontrol of aphids, the vectors of viruses, on seed potato plants in greenhouses

Summer greenhouses are used for the production of seed-potato mini-tubers in many Russian regions, so developing technologies for the effective and environmentally friendly protection of seed potatoes against insects that are vectors of viruses in greenhouses is relevant for domestic potato growing. Predatory coccinellids ( Coleoptera, Coccinellidae ) are successfully used for aphids’ control in greenhouses. However, these natural enemies have not yet been applied to protect seed-potato plants. This research is aimed at developing new approaches for applying Harmonia axyridis Pall. and Cheilomenes sexmaculatus Fabr. in the preventive biological control of aphids on seed-potato plants in greenhouses. Coccinellid larvae tolerance to fasting was evaluated in laboratory conditions at 24 °С and 60-70 % humidity. The optimal weight of the larvae to be preventively released into the greenhouses was determined. The IV instar larvae were kept with food in abundance for 1-2 days after molting. The larvae selected daily were grouped depending on their weight. The average time of starvation and the percentage of the individuals pupated were calculated for each size class of the larvae. To select indigenous coccinellids that can be used for aphid control on potatoes in greenhouses we monitored insects in natural habitats nearby the seed potato farm (Volosovskii Region, Leningrad Province). Monitoring of local entomophages and release of coccinellids were carried out in the seed potato farm. H. axyridis larvae were released in a film greenhouse (600 m2) on the potato plants of cultivar Red Scarlett. The experiment continued from June 12 to July 10, 2017. The number of coccinellids (larvae, pupae, and adults) was estimated weekly. It was shown that even a 2-day starvation of the H. axyridis II-III instar larvae caused an 8-12 % decrease in the survival rate. Therefore, their use unfits for preventive colonization of potato plants. It is optimal to use the IV instar larvae if they weigh enough for pupation with the likelihood about 50 %. We recommend releasing H. axyridis larvae weighted 20-29 mg and Ch. sexmaculatus larvae weighted less than 9 mg. H. axyridis IV instar larvae found on the plants at the seed farm 7 days after releasing averaged 22 % of the total released number. A decrease in the number of H. axyridis larvae and mass pupation occurred 14 days after when pupated individuals were 9.3 % of the initial larvae number. The emergence of the H. axyridis imago was observed 21 days after the release. The obtained results prove there are some good reasons for application of the H. axyridis IV instar larva in greenhouses on seed potatoes. Monitoring of aphidophages in their natural habitats near the greenhouses allowed us to select local species of coccinellids which are promising for potato plant protection in greenhouses. In June-July 2017, potato aphids ( Macrosiphum euphorbiae Thomas) appeared on nettle plants ( Urtica dioica L.). Adalia bipunctata L. (imago and larvae) and Coccinella septempunctata L. (larvae) were found in the pest hotspots. A. bipunctata imagoes may be used in greenhouses because this species needs lower prey abundance for egg laying and consumes most aphids colonizing potato plants.