Quality control of Telenomus remus (Hymenoptera: Platygastridae) reared on the factitious host Corcyra cephalonica (Lepidoptera: Pyralidae) for successive generations

Quality assessment of Telenomus remus successively reared on Spodoptera litura eggs for 30 generations

BACKGROUND

Telenomus remus (Nixon) is a dominant natural enemy controlling the invasive pest Spodoptera frugiperda (J. E. Smith). Continuous rearing of egg parasitoids on alternative hosts is crucial for mass production and cost reduction. However, to ensure the effectiveness of natural enemy products against target pests in the field, it is necessary to evaluate the parasitoid quality during the mass-rearing process. Despite the successful rearing of this parasitoid on the alternative host Spodoptera litura (Fabricius) eggs, less attention has been paid to the quality of parasitoids continuously reared for multiple generations. Therefore, we evaluated the performance of T. remus reared on S. litura eggs for 30 generations via morphological characteristics, flight ability, and life table analysis.

RESULTS

Wing length, wing width, body length, and right hind tibia length of T. remus did not differ among the different generations. However, the body length of female parasitoids was significantly longer than that of males for any generation. Although the proportion of 'flyers' and 'deformed' T. remus varied among generations, the flight ability did not decline significantly after rearing on S. litura eggs. Moreover, T. remus continuously reared on S. litura eggs maintained stable parasitism performance and life table parameters on the target host S. frugiperda eggs.

CONCLUSION

S. litura eggs are suitable hosts for the mass-rearing of T. remus. This study can be subsequently used to guide the production and facilitate the application of T. remus in the control of S. frugiperda. © 2023 Society of Chemical Industry.

Optimizing Photoperiod, Exposure Time, and Host-to-Parasitoid Ratio for Mass-Rearing of Telenomus remus, an Egg Parasitoid of Spodoptera frugiperda, on Spodoptera litura Eggs

Simple Summary

Telenomus remus (Nixon) is a promising natural enemy of Spodoptera frugiperda (J. E. Smith). Successful implementation of a biocontrol program requires a mature rearing system to produce millions of beneficial insect products at lower costs. This parasitoid is successfully reared on Corcyra cephalonica (Stainton) eggs in several countries, however that host species is unsuitable for Chinese strains of T. remus. Fewer studies have been done using Spodoptera litura (Fabricius) eggs, but it is increasingly seen as the promising alternative host in China. In order to identify optimal mass-rearing conditions when using S. litura eggs as an alternative host, this novel study thus sought to comprehensively evaluate the effects of photoperiod, exposure time, and host egg:parasitoid ratio on the reproductive potential and mass-rearing efficiency of T. remus on S. litura eggs. Our results suggest using more than 12 h of light, 24 h exposure time, and 14–20:1 host egg:parasitoid ratio for rearing T. remus on S. litura eggs. These findings will help promote successful, large-scale rearing of T. remus for use against S. frugiperda in China.

Abstract

Telenomus remus (Nixon) is a dominant egg parasitoid of the destructive agricultural pest Spodoptera frugiperda (J. E. Smith), and so is used in augmentative biocontrol programs in several countries. An optimized mass-rearing system is essential to produce biological control products in a timely and cost-effective manner. In this study, the photoperiod, host egg:parasitoid ratio, and exposure time were evaluated to identify the optimal rearing conditions for T. remus on the alternative host Spodoptera litura (Fabricius) eggs. Results showed that increasing photoperiod above 12L:12D remarkably improved parasitoid progeny yield and life table parameters. Overlong photoperiods shortened female longevity, but within acceptable limits. There was a significant negative correlation between parasitism rate and host egg:parasitoid ratio under exposure times of 12 and 36 h, but not 24 h. Percentage of female progeny increased significantly along with increasing the host egg:parasitoid ratio. A significant negative relationship between the number of emerged adults per egg and the host egg:parasitoid ratio was observed at an exposure time of 36 h. It was concluded that T. remus may be mass-reared most efficiently on S. litura eggs using a photoperiod of more than 12L:12D, a 14–20:1 host egg:parasitoid ratio, and an exposure time of 24 h. These findings can be used to produce T. remus more efficiently and at lower costs.

Integrative taxonomy and phylogeography of Telenomus remus (Scelionidae), with the first record of natural parasitism of Spodoptera spp. in Brazil

The egg parasitoid Telenomus remus (Hymenoptera: Scelionidae) has been investigated for classical and applied biological control of noctuid pests, especially Spodoptera (Lepidoptera: Noctuidae) species. Although T. remus was introduced into Brazil over three decades ago for classical biological control of S. frugiperda, this wasp has not been recorded as established in corn or soybean crops. We used an integrative approach to identify T. remus, combining a taxonomic key based on the male genitalia with DNA barcoding, using a cytochrome c oxidase subunit I mitochondrial gene fragment. This is the first report of natural parasitism of T. remus on S. frugiperda and S. cosmioides eggs at two locations in Brazil. We also confirmed that the T. remus lineage in Brazil derives from a strain in Venezuela (originally from Papua New Guinea and introduced into the Americas, Africa, and Asia). The occurrence of T. remus parasitizing S. frugiperda and S. cosmioides eggs in field conditions, not associated with inundative releases, suggests that the species has managed to establish itself in the field in Brazil. This opens possibilities for future biological control programs, since T. remus shows good potential for mass rearing and egg parasitism of important agricultural pests such as Spodoptera species.

Evaluating the Potential of Using Spodoptera litura Eggs for Mass-Rearing Telenomus remus, a Promising Egg Parasitoid of Spodoptera frugiperda

Simple Summary

Telenomus remus (Nixon) is an effective egg parasitoid for controlling Spodoptera frugiperda (J. E. Smith), which is a major destructive agricultural pest. Currently, this parasitoid is reared on Corcyra cephalonica (Stainton) eggs in several countries. However, previous studies carried out in China have reported that it cannot parasitize in C. cephalonica eggs. Meanwhile, those works have indicated that Spodoptera litura (Fabricius) can potentially be used as an alternative host. In order to evaluate this potential, our study compared the development and parasitism ability of T. remus on the eggs of S. frugiperda and S. litura at different temperatures in a laboratory. We found that S. litura eggs are more advantageous as an alternative host for the mass-rearing of parasitoid when compared with S. frugiperda eggs. Our results provide a more specific basis and reference for the large-scale production and low temperature storage of T. remus.

Abstract

Although Telenomus remus, a promising parasitoid of Spodoptera frugiperda, had been successfully reared on the eggs of Corcyra cephalonica in some countries, reports from China have argued that it is infeasible. Notably, studies from China have indicated that Spodoptera litura eggs could be a candidate host. Therefore, to further evaluate the potential of using S. litura eggs as hosts, we compared the development and parasitism of T. remus on the eggs of S. frugiperda and S. litura at temperatures between 20–32 °C. Our results showed that T. remus developed successfully on both host eggs at all of the tested temperatures, and the developmental duration and thermal requirements at each stage were similar between the two host species. The number of parasitized eggs was greater for S. litura than for S. frugiperda. Meanwhile, the emergence rate exceeded 86.6%, and it was significantly higher for S. litura than that for S. frugiperda, except at 29 °C. This study is the first time estimating the thermal requirements of T. remus at each stage. Moreover, we also recorded the morphological characteristics of T. remus at each stage. Our results demonstrate that S. litura eggs are more suitable than S. frugiperda eggs as an alternative host for the mass-rearing of T. remus in China. Understanding the thermal requirements and biological parameters contributes greatly to predicting the generation time and providing a reference for the mass-rearing and storage of the parasitoid.

A Comparison of Fitness-Related Traits in the Coleopteran Parasitoid Dastarcus helophoroides (Coleoptera: Bothrideridae) Reared on Two Factitious Hosts

The coleopteran parasitoid Dastarcus helophoroides (Fairmaire) (Coleoptera: Bothrideridae) is considered an efficient preventative method against the damage caused by a large number of cerambycid pests in China and other East Asian countries. Mass rearing of this parasitoid depends on screening appropriate factitious hosts. In this paper, the fitness-related traits of this parasitic beetle were explored using pupae of the two tenebrionid beetles, Tenebrio molitor Linnaeus and Zophobas morio Fabricius (Coleoptera: Tenebrionidae) as factitious hosts. The results showed that in dual-choice trials, D. helophoroides larvae preferred to attack Z. morio pupae. In no-choice trials, D. helophoroides reared on Z. morio pupae displayed significantly higher pupation and emergence rate, longer developmental duration of larval and larval-pupal stages, larger adult body size, shorter preoviposition period, more egg masses and egg production, and higher relative expected reproduction than those reared on T. molitor pupae. These results demonstrate that Z. morio is a more suitable factitious host for mass rearing of D. helophoroides.

Effect of the Ages of Parasitoid and Host Eggs on Telenomus podisi (Hymenoptera: Platygastridae) Parasitism

This study investigates the influence of parasitoid age and egg age of the hosts Euschistus heros (Fabricius) and Dichelops melacanthus (Dallas) on parasitism of Telenomus podisi Ashmead. Six separate bioassays were conducted: parasitism on eggs of E. heros (bioassay 1) and D. melacanthus (bioassay 2) by T. podisi females of different age (1, 5, and 10 days old); parasitism by T. podisi on eggs of different age (1, 2, 3, 4, and 5 days of embryonic development) of the hosts E. heros (bioassay 3) and D. melacanthus (bioassay 4); preference of T. podisi females for eggs at different embryonic developmental stages (eggs of 1, 2, 3, 4, and 5 days) of the hosts E. heros (bioassay 5) and D. melacanthus (bioassay 6). The age of T. podisi females and their hosts affected parasitism on both E. heros and D. melacanthus eggs. Overall, the parasitism rate was higher in older than younger parasitoids, independent of the tested host species, and host eggs between 1 and 3 days old were similarly parasitized. Thus, in T. podisi mass rearing facilities, it is recommended to use older adults (5 to 10 days old) as mother wasps to increase parasitism on the offered eggs. In addition, when hosts are completely absent in the field, or climatic conditions are unfavorable for release, mass-reared adults can be kept in the laboratory (25°C) for up to 10 days for later release in the field without any impairment of their subsequent parasitism performance.

Telenomus Remus, a Candidate Parasitoid for the Biological Control of Spodoptera Frugiperda in Africa, is already Present on the Continent

The fall armyworm, Spodoptera frugiperda, a moth originating from tropical and subtropical America, has recently become a serious pest of cereals in sub-Saharan Africa. Biological control offers an economically and environmentally safer alternative to synthetic insecticides that are being used for the management of this pest. Consequently, various biological control options are being considered, including the introduction of Telenomus remus, the main egg parasitoid of S. frugiperda in the Americas, where it is already used in augmentative biological control programmes. During surveys in South, West, and East Africa, parasitized egg masses of S. frugiperda were collected, and the emerged parasitoids were identified through morphological observations and molecular analyses as T. remus. The presence of T. remus in Africa in at least five countries provides a great opportunity to develop augmentative biological control methods and register the parasitoid against S. frugiperda. Surveys should be carried out throughout Africa to assess the present distribution of T. remus on the continent, and the parasitoid could be re-distributed in the regions where it is absent, following national and international regulations. Classical biological control should focus on the importation of larval parasitoids from the Americas.

Host Preferences of Telenomus podisi (Hymenoptera: Scelionidae): Parasitism on Eggs of Dichelops melacanthus, Euschistus heros, and Podisus nigrispinus (Hemiptera: Pentatomidae)

Successful biological control requires detailed knowledge about host preferences of the released parasitoid, because the presence of alternative hosts may affect the control of the target pest. The objective of this work was therefore to evaluate host preferences of Telenomus podisi Ashmead among the eggs of three stink bug species: Dichelops melacanthus Dallas, Euschistus heros Fabricius, and Podisus nigrispinus Dallas (Heteroptera: Pentatomidae). Three independent experiments were carried out to study host preferences among the following: (1) E. heros, D. melacanthus dallas, and P. nigrispinus (bioassay 1); (2) E. heros and D. melacanthus (bioassay 2); and (3) D. melacanthus and P. nigrispinus (bioassay 3). A single bioassay (bioassay 4) was carried out to evaluate the egg size of E. heros, D. melacanthus, and P. nigrispinus. Two more bioassays were carried out: bioassay 5 to study the biological characteristics of T. podisi reared on E. heros, D. melacanthus, and P. nigrispinus eggs, and bioassay 6 to study the morphological characters of T. podisi reared on those different host eggs. Overall, T. podisi consistently preferred eggs of D. melacanthus to those of the other studied hosts, due to probably their better nutritional value; hypothesis that is supported by the fast T. podisi development and bigger parasitoids when reared on D. melacanthus and P. nigrispinus eggs. This allows suggesting that neither pre-imaginal conditioning nor associative learning nor α-conditioning are relevant to T. podisi parasitism. Thus, E. heros eggs could be successfully used for mass rearing of this parasitoid for successive generations since it would not affect its parasitism on other species of the Pentatomidae family in the field.