Potential of Trichogramma achaeae (Hymenoptera: Trichogrammatidae) in Biological Control of Tuta absoluta (Lepidoptera: Gelechiidae) in Azorean Greenhouse Tomato Crops

An evaluation of the growth, development, reproductive characteristics and pest control potential of three Trichogramma species on Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae)

BACKGROUND

Tuta absoluta is an invasive alien species that has caused major losses in the Chinese tomato industry. Investigating the growth, development, reproduction and pest control effects of three native species of Trichogramma species on the eggs of T. absoluta could provide an ecological tool for preventing and controlling T. absoluta in China. In this study, we constructed age-stage two-sex life tables for three common species of Trichogramma and determined their relative abilities to control T. absoluta in greenhouse insect cages, thus allowing us to identify the species with the most effective ability to prey on T. absoluta eggs.

RESULTS

Analysis showed that the net reproductive rate (R0), gross reproduction rate (GRR) and intrinsic rate of increase (r) of Trichogramma ostriniae were the highest of the three species at 22.85, 32.58 and 1.31, respectively. In the presence of 10 eggs and under ideal conditions, T. ostriniae, Trichogramma chilonis, and Trichogramma dendrolimi produced 9451.04, 5199.56, and 1902.95 offspring, respectively. Following the release of T. ostriniae, tomato leaves incurred a damage index of 1 after the first week, while the number of T. absoluta reduced to 24.60 individuals by week 10 (8.75% of the control treatment).

CONCLUSION

Of the three species of Trichogramma tested in this study, T. ostriniae exhibited the best growth, development, reproductive capacity and predatory ability against T. absoluta, and has broad application prospects. © 2024 Society of Chemical Industry.

Feeding preference and intraguild interactions between the parasitoid Trichogramma achaeae and the predator Macrolophus pygmaeus, two biological agents of Tuta absoluta

BACKGROUND

Tuta absoluta is an exotic species and a major pest of tomato crops in Europe. Macrolophus pygmaeus and Trichogramma achaeae are two biocontrol agents widely used in integrated pest management programs of the South American tomato pinworm Tuta absoluta. In this study, we evaluated under laboratory conditions the (i) voracity of M. pygmaeus females fed on single diets of Tuta absoluta eggs parasitized or unparasitized by Trichogramma achaeae, (ii) voracity and feeding preference of M. pygmaeus females provided with mixed diets of Tuta absoluta eggs unparasitized and parasitized by Trichogramma achaeae and (iii) effect of competitive and intraguild interactions between M. pygmaeus and Trichogramma achaeae on the number of Tuta absoluta eggs consumed and/or parasitized. Lastly, we assessed under field conditions the effect of interspecific and intraspecific interactions between natural enemies on the number of Tuta absoluta eggs consumed and/or parasitized.

RESULTS

Macrolophus pygmaeus consumed more unparasitized than parasitized eggs of Tuta absoluta. Under mixed diet regimes, Manly indices revealed a feeding preference for unparasitized eggs, and a decrease in the total number of eggs consumed, as the proportion of available parasitized eggs increased, whereas the unparasitized eggs were consumed in direct proportion to their availability. Conspecific interactions between M. pygmaeus, in contrast to Trichogramma achaeae, revealed the possible occurrence of intraspecific competition. For intraguild heterospecific interactions, the number of Tuta absoluta eggs consumed by M. pygmaeus and parasitized by Trichogramma achaeae was lower than that predicted for additive and non-interactive scenarios. Under field conditions, a significant difference between the conspecific treatment and heterospecific treatments revealed a slightly higher success rate in controlling Tuta absoluta when both M. pygmaeus and Trichogramma achaeae were used simultaneously.

CONCLUSION

Macrolophus pygmaeus prefers unparasitized eggs of Tuta absoluta but inflicts intraguild predation on Trichogramma achaeae. In conspecific experiments, mutual interference between M. pygmaeus predators intensifies as the number of individuals increases, but for Trichogramma achaeae, it occurs in an unpredictable manner. Adding Trichogramma achaeae could significantly increase the level of control of Tuta absoluta compared to what could be achieved when only M. pygmaeus is present in glasshouse tomatoes. © 2023 Society of Chemical Industry.

Economic and financial model to the mass-rearing of Macrolophus pygmaeus (Rambur) (Heteroptera: Miridae), a biological control agent against the tomato moth Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) in protected culture

BACKGROUND

Tuta absoluta (Meyrick) is a major pest of tomato produced in glasshouses and open field, causing severe damages to crops, reducing the quality of tomato fruits. The current maintenance of the pest populations below the economic threshold is not achieved by natural and classical control, thus requiring the continuous application of biological control agents (BCAs), under an augmentative or inoculative approach. The present study aims to develop an economic and financial model to evaluate the commercial viability of a continuous mass production of Macrolophus pygmaeus (Rambur), a BCA commonly used against the tomato moth, Tuta absoluta, in protected culture. The estimations for our model were based on two approaches: the farm-level impact analysis and the benefit-cost analysis.

RESULTS

The results of the farm-level analysis show that the adoption of a more sustainable biological control approach is profitable for farmers and the benefit-cost analysis provides evidence that the investment on a new factory dedicated to the mass rearing of M. pygmaeus to control tomato moth populations generates a positive net present value (NPV) of 7.2 million euros, corresponding to an internal rate of return (IRR) of 28.4% per year.

CONCLUSION

Our results are in line with (i) the more recent European Commission proposals for a new Regulation on sustainable use of plant protection products, which includes the reduction of 50% the use and risk of chemical pesticides by 2030 and (ii) most of the existing literature which conclude that new projects on BCA production are worth investments. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Temperature Affects Biological Control Efficacy: A Microcosm Study of Trichogramma achaeae

Simple Summary

The performance of biological control agents (BCAs) under field conditions is of importance to successfully suppress pests following release. However, the quality of BCAs is usually evaluated with laboratory measurements under controlled conditions, which has been shown unable to predict the performance in complex field conditions. In this study, we quantified the quality of the parasitoid Trichogramma achaeae in microcosms at four constant temperatures and evaluated its ability to locate and parasitise pest eggs. We also compared parasitisation efficiency with fecundity as determined under laboratory conditions. We found the biological control efficacy as determined in our microcosms was strongly regulated by temperature and was unlikely to be predicted by laboratory fecundity. These findings suggest that more complex assays, including behavioural responses, might be developed to demonstrate the field quality of BCAs.

Abstract

Current quality control of mass-reared biological control agents (BCAs) is usually performed in the laboratory and often fails to include behavioural aspects of the BCAs. As a result, the use of efficacy measurements determined solely under laboratory conditions to predict field efficacy can be questioned. In this study, microcosms were designed to estimate biological control efficacy (realised parasitisation efficiency) of Trichogramma achaeae Nagaraja and Nagarkatti (Hymenoptera: Trichogrammatidae) parasitising Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) eggs across the operational temperature range (15–30 °C). Temperature greatly affected the success of females in finding and parasitising E. kuehniella eggs, with parasitisation being reduced at 15 and 20 °C, as both the percentage of parasitised host eggs and the percentage of leaves per plant with parasitised host eggs decreased sharply compared with higher temperatures. Graphing previous data on laboratory fecundity against parasitisation efficiency shows that the laboratory-measured fecundity of T. achaeae was unlikely to predict field efficacy across temperatures. Results also showed that leaf side had no effect on the preference of T. achaeae in parasitising E. kuehniella eggs; however, T. achaeae preferred to lay their eggs on the top tier of plants. These findings suggest that more complex assays, which include behavioural responses, might be developed for optimised quality control of BCAs intended for field application.

Suitability of European Trichogramma Species as Biocontrol Agents against the Tomato Leaf Miner Tuta absoluta

The tomato leaf miner Tuta absoluta, originally from South America, is an invasive species threatening European tomato crops. Since various insecticides have become ineffective in controlling T. absoluta, effective and environmentally friendly alternatives are needed. Biological control, especially by Trichogramma parasitoids, is considered to be an effective means of reducing this pest. Thus, the aim of our study was to identify promising candidates of Trichogramma parasitoids for biological control of T. absoluta in Europe. We assessed the efficiency of nine European Trichogramma species and compared them to Trichogramma achaeae, as this species is already commercially available. Firstly, we verified species identity of the 10 rearing strains using molecular and morphological methods. Then, host acceptance, host preference (T. absoluta vs. rearing host Sitotroga cerealella eggs) and host searching capacity were tested under laboratory conditions. Our results indicated that T. nerudai, T. pintoi and T. cacoeciae achieved a similar level of parasitism on potted tomato plants as T. achaeae. For the next step, these promising strains should be tested under greenhouse conditions.

Oviposition-Induced Volatiles Affect Electrophysiological and Behavioral Responses of Egg Parasitoids

In response to an attack by herbivores, plants emit a variety of compounds that may act as semiochemicals. Oviposition-induced volatiles (OIPVs) have been shown to mediate interactions between plants and natural enemies. Here, we investigated the role of OIPVs by Tuta absoluta towards two egg parasitoids, Trichogramma cordubense and T. achaeae. We collected headspace volatiles from tomato plants at 24, 48, and 72 h after oviposition by T. absoluta females and tested the antennographic response of Trichogramma parasitoids to them by means of gas chromatography- electro-antennographical detection (GC-EAD). The response of the parasitoids was also tested in behavioral experiments using a Y-tube olfactometer. Oviposition by T. absoluta females induced qualitative and quantitative changes in the volatiles emitted by tomato plants. Antennae of Trichogramma parasitoids responded to several of the induced volatiles in GC-EAD. T. cordubense females were attracted to tomato plants with T. absoluta eggs 24 h after oviposition. The elucidation of the behavior of egg parasitoids towards OIPVs enhances the development of sustainable management strategies either by selecting species that exploit OIPVs or by manipulating their foraging behavior by utilizing specific OIPVs that are used by parasitoids as a host location.