The effect of false codling moth (Thaumatotibia leucotreta) larval growth stages on ‘Midknight’ valencia citrus fruit biochemical properties, selected secondary metabolites and antioxidant activities.

Abstract

Worldwide, citrus is the most produced crop and accounts for the biggest export in South Africa. Citrus is a tropical crop; therefore, it is a major host of several phytosanitary pests, including false codling moth (Thaumatotibia leucotreta) (FCM). False codling moth is known for fruit damage; and therefore, restricted on certain lucrative international markets. However, there is an information gap on how FCM larvae affect citrus fruit biochemical attributes, secondary metabolites as well as antioxidant activities. Therefore, the study evaluated the effect of false codling moth (Thaumatotibia leucotreta) larval growth stages on ‘Midknight’ valencia citrus fruit biochemical properties, selected secondary metabolites and antioxidant activities. In this experiment, matured ‘Midknight’ valencia citrus fruit were harvested from Joubert en Seuns farm in Schoemanskloof and transported to the University of Mpumalanga, Nelspruit, South Africa for treatment and quality evaluation. The ‘Midknight’ valencia citrus fruit were exposed to the following treatments: T0 = no FCM larvae, T1 = fruit were exposed to first instar FCM larvae and T2 = exposed until second instar FCM larvae. For the first and second instar treatment, fruit were exposed to larvae for 3 and 12 days, respectively, then squeezed and tested for total soluble solids (TSS), titratable acids (TA), total phenolic contents (TPC) as well as total flavonoid contents (TFC), and total antioxidants using the ferric reducing power (FRAP), 2,2-azinobis (3-ethyl-benzothiazoline-6-sulfonic acid (ABTS) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) assays. The results showed that false codling moth first and second instar did not affect (p > 0.05) the TSS, TA as well as the antioxidant activity measured by ABTS of fruit. However, FCM larval growth stages had a significant influence (p < 0.05) on ‘Midknight’ valencia citrus fruit TPC, TFC and antioxidant activity quantified by FRAP and DPPH. False codling moth first instar had a great influence on phenolic compounds (Figure 3.2 and 3.3) and antioxidant activities quantified by DPPH (Figure 4.3) compared to the second instar. Meanwhile the second instar greatly affected antioxidant activities quantified by FRAP (Figure 4.1). In conclusion, false codling moth (Thaumatotibia leucotreta) had no influence on biochemical attributes but affected the selected secondary metabolites and antioxidant activity of ‘Midknight’ valencia fruit.