Gene Characterization and Enzymatic Activities Related to Trehalose Metabolism of In Vitro Reared Trichogramma dendrolimi Matsumura (Hymenoptera: Trichogrammatidae) under Sustained Cold Stress.

Xin Lü,Li-Ying Li,Jun Li,Zhi-Gang Li,Shi-Chou Han

doi:10.3390/insects11110767

Abstract

Simple SummaryTrehalose is a non-reducing disaccharide that presents in a wide variety of organisms, where it serves as an energy source or stress protectant. Trehalose is the most characteristic sugar of insect hemolymph and plays a crucial role in the regulation of insect growth and development. Trichogramma species are economically important egg parasitoids, which are being mass-produced for biological control programs worldwide. Many Trichogramma species could be mass reared on artificial mediums (not insect eggs), in which components contain insect hemolymph and trehalose. These in vitro-reared parasitoid wasps were strongly affected by cold storage, but prepupae could be successfully stored at 13 °C for up to 4 weeks. The aims of the present study were to determine the role of trehalose and the relationship between trehalose and egg parasitoid stress resistance. Our study revealed that (1) trehalose regulated the growth under sustained cold stress; (2) prepupal stage is a critical developmental period and 13 °C is the cold tolerance threshold temperature; (3) in vitro reared Trichogramma dendrolimi could be reared at temperatures of 16 °C, 20 °C, and 23 °C to reduce rearing costs. This finding identifies a low cost, prolonged development rearing method for T. dendrolimi, which will facilitate improved mass rearing methods for biocontrol.Trichogramma spp. is an important egg parasitoid wasp for biocontrol of agriculture and forestry insect pests. Trehalose serves as an energy source or stress protectant for insects. To study the potential role of trehalose in cold resistance on an egg parasitoid, cDNA for trehalose-6-phosphate synthase (TPS) and soluble trehalase (TRE) from Trichogramma dendrolimi were cloned and characterized. Gene expressions and enzyme activities of TdTPS and TdTRE were determined in larvae, prepupae, pupae, and adults at sustained low temperatures, 13 °C and 16 °C. TdTPS and TdTRE expressions had similar patterns with higher levels in prepupae at 13 °C and 16 °C. TdTPS enzyme activities increased with a decrease of temperature, and TdTRE activity in prepupae decreased sharply at these two low temperatures. In vitro reared T. dendrolimi could complete entire development above 13 °C, and the development period was prolonged without cold injury. Results indicated trehalose might regulate growth and the metabolic process of cold tolerance. Moreover, 13 °C is the cold tolerance threshold temperature and the prepupal stage is a critical developmental period for in vitro reared T. dendrolimi. These findings identify a low cost, prolonged development rearing method, and the cold tolerance for T. dendrolimi, which will facilitate improved mass rearing methods for biocontrol.

Highlights

Sugars are used for energy production and are stored as glycogen in the body fat, or as trehalose in the hemolymph [1,2,3]
To identify the TdTPS and TdTRE, cDNA fragments involved in trehalose metabolism were identified through T. dendrolimi transcriptome data (Hiseq 2000, Illumina, Santiago, USA)
The results suggest that sustained low temperature has a strong effect on the expression level of trehalase genes in T. dendrolimi, which may facilitate the utilization of trehalose

Summary

Introduction

Sugars are used for energy production and are stored as glycogen in the body fat, or as trehalose in the hemolymph [1,2,3]. Trichogramma are egg parasitoid wasps that obtain diverse nutrients, including sugars, from their host eggs during development. Trichogramma dendrolimi Matsumura is an important biological control agent that has been mass produced on eggs of Corcyra cephalonica (Stainton) and Antheraea pernyi (Guérin-Méneville) for biological control programs in China [4,5]. Artificial host eggs are used to mass produce T. dendrolimi [6,7]. Lü et al [8,9,10] developed an artificial medium containing trehalose for the continuous rearing of T. dendrolimi and revealed that trehalose was an essential ingredient of the artificial media. Biochemical characteristics, including trehalose content and trehalase activity in T. dendrolimi, continuously reared on artificial medium (in vitro) versus those reared on A. pernyi eggs (in vivo), were studied [11]. The quality of in vitro reared T. dendrolimi was strongly affected by cold storage, but prepupae could be successfully stored at 13 ◦ C for up to 4 weeks [12]

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