Effects of cold storage on the chemical composition of Corcyra cephalonica eggs by ¹H NMR spectroscopy

Highlights

• 56 compounds were identified from rice moth eggs.

• Cold storage resulted in changes to the chemical composition of rice moth eggs.

• Alanine, glutamine, glucose and acetate contributed to the observed difference.

Abstract

Rice moth Corcyra cephalonica eggs, frequently utilized as factitious hosts of Trichogramma wasps, are usually cold-stored for a period of time in order to meet the need of Trichogramma mass rearing. However, compounds in cold stored C. cephalonica eggs can influence the quality and quantity of Trichogramma. In the present study, we used Hydrogen-1 Nuclear Magnetic Resonance (¹H NMR) spectroscopy and multivariate statistical analysis to investigate the effect of cold storage on the chemical composition of fresh rice moth eggs (U) and killed embryo eggs cold stored at 4 °C for 0 (CK), 15 (N15), 30 (N30), 45 (N45), and 60 (N60) days, respectively. A total of 56 compounds were identified and quantified for each treatment, including amino acids, nucleic acid components, organic acids, sugars, and amides. Principle component analysis (PCA) and partial least square discriminant analysis (PLSDA) demonstrated that cold storage had a pronounced effect on the chemical composition of rice moth eggs. Three groups, U and CK, N15 and N30, and N45 and N60, were classified by their components’ similarity. The primary components that contributed to difference among three groups were alanine, glutamine, glucose and acetate, the concentrations of which significantly changed with the increasing of cold storage days. Thus, cold storage elicits changes in the chemical compositions of rice moth Corcyra cephalonica eggs, which may affect the growth and development of Trichogramma.

Introduction

Trichogramma (Hymenoptera: Trichogrammatidae) wasp is one of the most successful biological control agents of agricultural and forest insect pests (Huffaker and Messenger, 1976, Li, 1994, Consoli et al., 2010). These wasps demonstrate a wide range of hosts, extensive distribution, abundant species resources, and easy mass rearing and are now used world-wide to control insect pests, especially for lepidopterous pests such as Ostrinia furnacalis, Mythimna separata and Chilo venosatus (Ebrahimi, 1999, Herz et al., 2007, Poorjavad, 2011). The host eggs are an important nutritional resource for parasitoids and, as such, are known to influence a wide range of physiological and behavioral aspects of egg parasitoids (Grenier et al., 1986, Farahani et al., 2016). The eggs of the rice moth Corcyra cephalonica (Stainton) (Lepidoptera: Galleriidae) are commonly used as a host for Trichogramma mass rearing in China (Wang et al., 2014). Amassing a sufficient quantity of rice moth eggs is a crucial part of mass rearing and of successful release of Trichogramma in the field.

To meet the requirement of the large-scale industrialized production of Trichogramma and to reduce waste of biological material, ultraviolet ray (UV) and refrigeration are often used to prolong the storage period of host eggs. Eggs of C. cephalonica exposed to UV can be easily parasitized by Trichogramma and can prevent the larva of C. cephalonica from eating the parasitic eggs (Tuncbilek et al., 2009).

Host eggs stored at low temperatures can extend storage periods and meet the high demands for the production and release of Trichogramma. However, long-term storage of host eggs could lead to detrimental effects that can reduce host acceptance, host recognition, percent parasitism and percent emergence (Flanders, 1938, Leopold, 1998, Kostal et al., 2004, Kostal et al., 2006, Krechemer and Foerster, 2016). In T. brassicae it was found that there was a negative relationship between the level of parasitism and cold storage time (Nazeri et al., 2015). Limiting the period of storage at low temperature was also a crucial factor to control the decline in host quality. Pan et al. (2011) had found that T. dendrolimi had a weaker parasitizing capacity and lower emergence rate in rice moth eggs stored at low temperature for a long time, which was also demonstrated in previous studies (Zhang et al., 2008). Some species of egg parasitoids showed no negative consequences when host eggs were exposed to 2–10 °C for one month (Greco and Stilinovic, 1998, Kivan and Kilic, 2005, Chen and Leopold, 2007, Mahmoud and Lim, 2007, Alim and Lim, 2010).To keep good quality levels in Trichogramma rearing, research has suggested that the storage period for rice moth eggs at 4 °C should not exceed 15 days (Zhang et al., 2008).

The Trichogramma larvae absorb and digest nutrition from host eggs. Thus the composition of host eggs, the basic qualitative nutritional requirements of Trichogramma, has a great effect on their growth, development and reproductive behavior (Farahani et al., 2016). Extensive research has been carried out to investigate the nutrient requirements for the oviposition of egg parasitoid wasps (Ayvaz and Karabörklü, 2008, Barrett and Schmidt, 1991, Nettles et al., 1985). However, systematic research of composition of rice moth eggs has not been reported, and further studies are needed to elucidate the internal mechanism impacting host behavior.

Increasing evidence showed that eggs in cold storage had critical effects on the reproduction and breeding of Trichogramma, but it is not clear what changes happen in the rice moth eggs when refrigerated. In this study, we comparatively investigated the contents of C. cephalonica eggs in fresh and cold storage over various time periods at 4 °C to reveal the effects of cold storage on the chemical compositions of rice moth eggs using Nuclear Magnetic Resonance (NMR) technology and multivariate statistical analysis.