Effect of nutritional interaction between plant growth stimulants and peach green aphid (Myzus persicae Sulzer) on physiological processes of two-spotted ladybird (Adalia bipunctata L.)

The effects of plant growth-promoting activities involving biological, chemical, and organic fertilizers are partly well studied for pest insects. Still, studies concentrating on the impacts of such treatments on predators are uncommon. Plant growth promoting treatments- biological, -organic and -chemical fertilizers alter the biochemical composition of plants, which can impact the multitrophic interactions. Beneficial soil microorganisms such as plant growth-promoting rhizobacteria (PGPR) can affect nutritional quality, secondary metabolites, enzymes, phytohormones, and volatile organic compounds (VOCs) of plants, which may influence host plant-insect herbivore- natural enemies interactions. The predatory ladybird, Adalia bipunctata, is polyphagous species that mainly feed on aphids, especially the green peach aphid, Myzus persicae. It is a polyphagous insect that can cause damage to a lot of crops in fields and greenhouses. There is no published research concerning the effects of various plant growth-promoting on physiological performance of A. bipunctata. Thus, we investigated the impacts of various plant growth promoting treatments, viz. no fertilizer (untreated control), one type of PGPRs, vermicompost 30% (v/v), and zinc sulfate on physiological performance of A. bipunctata through M. persicae reared on treated Capsicum annum L. (Solanaceae).

Bell pepper seeds of the California Wonder cultivar were developed in 3L plastic pots and were used in bioassays when they reached 4-6 leaf stage under greenhouse conditions. Then, aphids were obtained from tomato farms from Meshkin-Shahr (Ardabil, Iran) and transmitted to bell pepper grown in the greenhouse. To keep an appropriate sub-sucking colony, every week the individuals were transferred from infested bell peppers to fresh plants. Adults of A. bipunctata were obtained from alfalfa farms of Ardabil, Iran, and transmitted to the laboratory, in a growth chamber. Mating pairs were selected and kept together in separate plastic jars (6 by 12 cm2) and were reared on pepper plants infested with sub-sucking insects as prey. In the study, the effect of spraying zinc sulfate on bell pepper plants and addition of the organic fertilizer of vermicompost 30% and the biologic fertilizers of Bacillus subtilis to the growing medium of bell pepper on the activities of critical physiological processes of A. bipunctata fed on M. persicae using a completely randomized design under greenhouse conditions. Then 5 adult predators were randomly selected from each treatment and homogenized with a hand pounder in 1 mL pure ice-cold water. After that, the specimens were centrifuged at 13,000 g pending 15 min at 4 ◦C. The top layer was collected and kept at 20 ◦C during biochemical analyses. All physiological enzymes assay based on the defined method were conduted in three biological replications. Then, data were analyzed using a one-way analysis of variance (ANOVA) followed by the Tukey test with the MINITAB software.

The results demonstrated a significant difference among the digestive enzymes activities, intermediates, and storage compounds of the predatory ladybug reared on aphids fed on bell peppers treated with different fertilizers. The lowest total protease activity of ladybird was observed in the control compared to other treatments. The elastase activity of ladybug increased on B. subtilis compared to other treatments. The highest and lowest amounts of cathepsin B activity in ladybugs were recorded on B. subtilis and vermicompost 30%, respectively. The highest and lowest low density lipophore (LDL) values were observed in A. bipunctata on control and B. subtilis treatment, respectively. Predatory ladybug had the highest protein, triglyceride, and glycogen on B. subtilis compared to other treatments. The lowest triglyceride and glycogen was also observed on vermicompost 30%.

Plant-herbivore interactions under the influence of bio-fertilizer have led to increased digestive enzymes activity and storage compounds in ladybug, which could be used in combination with the use of biological control agents in integrated management programs of the green peach aphid in greenhouses.