Elsevier

Crop Protection

Volume 141, March 2021, 105425
Crop Protection

Effect of cold storage on the viability of Exorista japonica (Townsend) (Diptera: Tachinidae) pupae of an important parasitoid of noctuid larvae

https://doi.org/10.1016/j.cropro.2020.105425Get rights and content

Highlights

  • Cold storage had an effect on emergence, fecundity, and longevity of E. japonica.

  • Storage of E. japonica pupae at 10 °C was deleterious to its emergence.

  • E. japonica pupae can be stored up to 3 weeks at 4 °C.

Abstract

Exorista japonica (Townsend) is a polyphagous parasitoid that attacks several lepidopteran pest species and it has been well known as a powerful natural enemy showing the high parasitism on noctuid larvae. For usage of this parasitoid in biological control of insect pest larvae, we established the effective storage condition for stockpiling this parasitoid. Emergence rate of E. japonica pupae stored at 4.0 °C, emergence rate was higher than that at other cold storage temperature conditions. Storage at 10.0 °C was deleterious to the parasitoids’ emergence below 50.0% emergence rate. Preconditioning by exposing pupae to 10.0 °C for 72 h before storage at 4.0 °C showed a significant low emergence rate, even though female longevity was relatively high. Cold storage durations had a significant effect on emergence, fecundity, and female longevity. After 4 weeks storage at 4.0 °C, emergence rate significantly decreased. The fecundity and longevity of female significantly decreased even though pupae were stored at 4.0 °C for only 1 week. Cold storage had an effect on sex ratio, fecundity, and female longevity of F1 progeny. The proportion of females in F1 progeny produced by cold stored individuals was much higher than that of the control. Cold storage may decrease the quality of parasites. However, E. japonica pupae can be successfully stored up to 3 weeks so that sufficient supply of this parasitoid at a release time would be possible through a mass production with a cold storage.

Introduction

Tachinid flies belong to the largest and most important group of non-hymenopteran parasitoids, group of Tachinidae (Diptera). (Nakamura, 1994; Feener and Brown, 1997). Tachinid flies play an important role in regulating phytophagous insect population (Hanyu et al., 2009). Among them, Exorista japonica Townsend has been reported to attack several lepidopteran pest species, particularly noctuid larvae including the common armyworm, Mythimna separata, the common cutworm, Spodoptera litura, and the fall webworm, Hyphantria cunea (Shima, 2006). Even though more than 40 species of tachinids have been reported as larval or larval-pupal parasitoids of H. cunea throughout the world, there has been a little field research on its use as biocontrol agents during the last few decades (Konno, 1998; Kan et al., 2003).

Exorista japonica lays heavy-shelled, highly visible macrotype eggs on the host caterpillars’ cuticle (Nakamura, 1994), mainly on the head and thoracic segments of the host (Dindo and Nakamura, 2018). After several days of incubation, the newly hatched larvae penetrate into the inside of host integument from the cuticle, induce the formation of a primary integumental respiratory funnel and continuously develop until pupation (Nakamura, 1994). After fully grown within the host, they escape from the exit hole on the host in a pre-pupa stage so that parasitized hosts eventually die.

Cold storage is an effective technique to extend the life of natural enemies (Mousapour et al., 2014). Therefore, this method has been considered as a valuable tool in the mass rearing systems of biological control agents because it provides a stable supply by maximizing the flexibility and efficiency in mass production (Leopold, 1998). However, cold exposure may affect longevity (Starý, 1970), mortality (Sømme, 1982; Leather et al., 1993), and reproduction of insects (Carrière and Boivin, 2001). Exposures to low temperature may produce cumulative physiological damages and lead to a high level of mortality or selection of individuals with poor reproductive success (Levie, 2002).

In order to stock up natural enemies for biological control, entomophagous insects have been attempted to store as different developmental stages such as eggs, larval instars or nymphs, pre-pupae, pupae, and adults. Among these stages, pupal stage was considered to be the most appropriate stage for long term cold storage (Jalali and Singh, 1992; Rathee and Ram, 2018). Therefore, many researches have been carried out to examine the effects of cold storage on the performance of natural enemies, so most works have focused on the pupal stage (Chen et al., 2008). Telenomus remus Nixon was able to be stored as pupal stage at 10 °C for 7 days without the negative effect on its survival (Gautam, 1986). Survivals of Venturia canescens immatures were largely affected by low temperature conditions (0, 5, and 10 °C), whereas they were minimally damaged under 15 °C (Press and Arbogast, 1991). When cocoons of Allorhogas pyralophagus Marsh, a Mexican parasitoids of graminaceous borers were stored for more than 14 days at 2 °C, they failed to survive. But, under storage for over 21 days at 5 and 10 °C, approximately 50% of stored insects could be survived (Ballal et al., 1989). Also, Telenomus busseolae pupae could be stored for 4 weeks at 4 and 8 ± 1 °C, but more than 2 week storage at 12 ± 1 °C was not suitable due to high mortality (Bayram et al., 2005).

Several factors such as survival, sex ratio, reproductive ability, and behavior must be considered before implementing cold storage of biological control agents for practical purposes (Etzel and Legner, 1999). Under cold storage conditions, the fitness traits or quality of natural enemies may be affected by the characteristics passed onto progeny. Therefore, it is a crucial step to build up of sufficient number of biological control agents for mass release as needed continually (Bayram et al., 2005).

The aim of this study is to evaluate the quality of E. japonica pupae after cold storage. We investigated the effects of different low temperatures and storage durations on the emergence rate, adult longevity, and fecundity of E. japonica in order to determine the optimal cold storage conditions for large quantities of this parasite. Additionally, we examined the effects of cold storage on sex ratio, fecundity, and adult longevity of F1 progeny produced from cold stored adults.

Section snippets

Experimental insects

The tachinid fly, E. japonica was originated from the parasitized larvae of Mythimna separata collected on gramineous weeds in Gimje, Jeonbuk Province (35.8 ‘N, 126.8’ E) on late July 2015. This colony has been maintained at air conditioned rearing room (25 ± 1 °C, 50–65% RH, and 14 L:10D photoperiod) with 4th or 5th larvae of Spodoptera litura as host larvae reared with an artificial diet since then. These flies were reared in an acryl cage (24 × 15 × 18㎝) and 20 ml glass vial containing

Effect of cold storage on E. japonica adult emergence and longevity

There were significant differences in emergence and female longevity after cold storage among control and cold storage temperatures of E. japonica. Under cold storage for 2 weeks, the emergence of E. japonica pupae stored at 4 °C was significantly higher than that at 10 °C (F3,16 = 13.67, P = 0.000). There was no significant difference in longevity of males storage temperature conditions (F3,16 = 2.04, P = 0.136), but storage temperature significantly affected female longevity (F3,16 = 20.05, P

Discussion

The current study shows that several tachinid parasitoids can be stored at cold temperature conditions in a young larva or pupae stage for a short period. For example, the tachinid parasitoid, Compsilura concinnata successfully was stored as a young larva in the host or a puparium for 2–4 weeks at 10–15.6 °C (Fusco et al., 1978). Another tachinid parasitoid, Archytas marmoratus was stored as maggot for a few days at 13 °C (Gross and Johnson, 1985). Besides tachinids, it has been reported that

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

This research was supported by Agenda Research Project (PJ010945) of Rural Development Administration.

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