Transgenerational stability of a high temperature-adapted strain of Neoseiulus barkeri Hughes (Acari: Phytoseiidae) and differential expression of antioxidant genes in response to heat stress

Abstract

High temperature-adapted natural enemies may exhibit improved biocontrol effiicacy in hot weather, but transgenerational stability of the trait may affect practical applications. Neoseiulus barkeri is a commercially produced biocontrol agent, and a high temperature-adapted strain (HTAS) has been developed. Thermotolerance and the activity of antioxidant enzymes were evaluated in HTAS progeny under non-selective conditions to determine transgenerational stability of the selected adaptation. Results showed that survival of HTAS offspring decreased slightly after heat stress compared to HTAS parents, but remained significantly higher than that of the conventional strain (CS). LT₅₀ and LT₉₅ values of HTAS progeny were similar to HTAS parents and were approximately 2.5 and 4 h greater than CS, respectively. Similarly, predation behavior of HTAS offspring decreased somewhat compared to HTAS parents after short-term heat stress, but remained significantly higher than that of CS mites. Searching rate (a) of HTAS progeny was similar to HTAS parents and noticeably higher than CS, whereas handling time (T_h) was lower than CS mites. Activities of both superoxide dismutase (SOD) and glutathione S-transferase (GST), along with malondialdehyde (MDA) content and total antioxidant capacity (T-AOC), were lower in HTAS offspring compared to HTAS parents and the CS, whereas peroxidase (POD) and catalase (CAT) activities were higher. The expression levels of ten antioxidant genes in HTAS offspring were significantly lower than in HTAS parents or CS mites before heat stress, but reached or surpassed parental levels after heat stress. Correlation analysis found both positive and negative associations between antioxidant indices and antioxidant genes. These results suggest that thermotolerance in the HTAS is relatively stably across generations in the absence of selective pressure, and is associated with changes in expression of antioxidant genes.