Non-target effects of ten essential oils on the egg-parasitoid Trichogramma evanescens

Essential oils (EOs) are increasingly used as biopesticides due to their insecticidal potential. This study addresses their non-target effects on a biological control agent: the egg parasitoid Trichogramma evanescens. In particular, we tested whether EOs affected parasitoid fitness either directly, by decreasing pre-imaginal survival, or indirectly, by disrupting parasitoids' orientation abilities. The effect of Anise, Fennel, Sweet orange, Basil, Coriander, Oregano, Peppermint, Mugwort, Rosemary and Thyme EOs were studied on five strains of T. evanescens. Specific experimental setups were developed, and data obtained from image analysis were interpreted with phenomenological models fitted with Bayesian inference. Results highlight the fumigant toxicity of EOs on parasitoid development. Anise, Fennel, Basil, Coriander, Oregano, Peppermint and Thyme EOs are particularly toxic and drastically reduce the emergence rate of T. evanescens. Most EOs also affect parasitoid behavior: (i) Basil, Coriander, Oregano, Peppermint, Mugwort and Thyme EOs are highly repellent for naive female parasitoids; (ii) Anise and Fennel EOs can have repellent to attractive effects depending on strains; and (iii) Sweet orange, Oregano and Rosemary EOs have no detectable impact on orientation behavior. This study shows that EOs fumigation have non-target effects on egg parasitoids. This highlights the need to cautiously precise the deployment framework of biopesticides in an agroecological perspective.

Attraction of Trichogramma Wasps to Butterfly Oviposition-Induced Plant Volatiles Depends on Brassica Species, Wasp Strain and Leaf Necrosis

Within the Brassicaceae, wild as well as crop species are challenged by specialist herbivores including cabbage white butterflies (Pieris spp.). The wild crucifer Brassica nigra responds to oviposition by Pieris butterflies by the synergistic expression of two egg-killing traits. Genotypes that express a hypersensitive response (HR)-like necrosis (direct egg-killing) also emit oviposition-induced plant volatiles (OIPVs) attracting Trichogramma egg parasitoids (indirect egg-killing). This so-called double defense line can result in high butterfly egg mortalities. It remains unknown whether this strategy is unique to B. nigra or more common in Brassica species. To test this, we examined the response of different Trichogramma evanescens lines to OIPVs emitted by B. nigra and three close relatives (Brassica napus, Brassica rapa, and Brassica oleracea). Furthermore, we evaluated whether HR-like necrosis played a role in the attraction toward plant volatiles. Our results show a specificity in wasp attraction to different plant species. Three out of four plant species attracted a specific T. evanescens strain, including the crops B. rapa and B. napus. Parasitoid attraction was positively affected by presence of HR-like necrosis in one plant species. Our findings imply that, despite being a true generalist in terms of host range, T. evanescens shows intraspecific variation during host searching, which should be taken into account when selecting parasitoid lines for biocontrol of certain crops. Finally, we conclude that also crop plants within the Brassicaceae family possess egg-killing traits and can exert the double-defense line which may enable effective selection of egg-killing defense traits by cabbage breeders.

Cold storage-mediated rearing of Trichogramma evanescens Westwood on eggs of Plodia interpunctella (Hübner) and Galleria mellonella L.

The egg parasitoid Trichogramma evanescens Westwood is considered as an efficient biological control agent for managing several lepidopteran pests and it is widely distributed throughout the world. Mass rearing protocols of parasitoids that are currently in use in biocontrol programs require a meticulous quality control plan, in order to optimize their efficacy, but also their progeny production capacity. In this paper, the effect of different factors on the quality control in mass rearing of T. evenescens, using Plodia interpunctella (Hübner) and Galleria mellonella L. as host species, were investigated. The impact of egg agewas significant in the rates of parasitism, for both host species tested. Significantly highest percent of parasitoid emergence was noticed in two day-old eggs for both host species, while one day-old eggs day exhibited the maximum emergence when both species were used togetherin the same trials. Age-dependent storage egg preservation at either 4 or 9°C significantly influenced the parasitism percentages on both species. The highest parasitism percentage was recorded in two day-old G. mellonella eggs that are kept for 15 days at 9°C while the lower in one day-old P. interpunctella eggs for 60 d storage. Moreover, the highest parasitoid mortality was recorded in T. evanescens reared either on P. interpunctella or G. mellonella at 20°C. Rearing of the parasitoid on a mixture of eggs of both host species resulted in higher parasitism, but not always in higher rates of parasitoid emergence. The results of the present work provide useful information that can be further utilized in rearing protocols of T. evanescens.

Laboratory evaluation of the possibility of using the eggs of the chestnut moth Cameraria ohridella Deschka & Dimic, 1986 (Lepidoptera: Gracillariidae) to feed the trichogram

Goal. Evaluation of the suitability and eggs of chestnut moth Cameraria ohridella for parasitism and development of trichogramma. Methods. Laboratory cultures of Trichogramma pintoi Voeg were used for research. and Trichogramma evanescens Westw., which were bred on the eggs of Sitotroga cerealella Oliv. The experiment was performed according to the following scheme: female trichogramma after mating was placed in a test tube in 5 replicates for each species. The tube was closed with a stopper and the sex of individuals under binoculars was checked. In test tubes with trichogram laid strips of paper with one-day eggs of chestnut moth (25 copies.). In 5 replicates and kept in a thermostat (temperature — 24—25°C; relative humidity — 65—67%). The percentage of trichogram revival and the ratio of males to females, life expectancy and fertility of females were determined. Trichogramma individuals, which were fed with grain moth eggs, served as controls. The experiment lasted until the complete death of the trichogram. The obtained results were processed statistically according to standard methods. Results. A small number of chestnut moth eggs pierced by trichogramma were detected, but embryonic development of the parasite’s eggs was not observed. Comparing the size of the eggs of the chestnut moth with the size of the eggs of the main squamous pests against which different species of trichogramma are effectively used, we can conclude that for the successful development of eggs T. pintoi and T. evanescens chestnut moth eggs are not suitable as feeders. Probably, in terms of size and biological quality, they do not correspond to the parameters of the ecological niche of the hosts of the family Trichogrammatidae. Conclusions. In the laboratory, it was found that the eggs of the chestnut moth are not suitable for parasitizing the trichogramma of T. pintoi and T. evanescens. The main pests of crops, which are effectively parasitized by different species of trichogramma, have an egg size in the range of 0.4—1.0 mm, while the size of chestnut moth eggs does not exceed 0.27—0.32 mm. It is possible that the size and biological quality of chestnut moth eggs do not meet the parameters of the ecological niche of entomophagous feeders of the family Trichogrammatidae. Further researches with use of various types of a trichogramma, first of all — T. dendrolimi Mats appear actual.

Role of host diet on the fitness of the egg parasitoid species, Trichogramma evanescens Westwood (Hymenoptera: Trichogrammatidae)

Background Egg parasitoids belonging to the genus Trichogramma (Hymenoptera: Trichogrammatidae) are important natural enemies that have been successfully used in biological control programs and mostly reared on the Mediterranean flour moth, Ephestia kuehniella (Zeller) (Lepidoptera: Pyralidae). Host quality is a crucial factor that can determine parasitoid fitness. Main body Laboratory studies were carried out to evaluate the effects of 3 different larval diets CY diet (95% cornmeal + 5% yeast), CBGY diet (53.3% cornmeal + 26.7% wheat bran + 15% glycerine + 5% yeast), and WBGY diet (53.3% wheat flour + 26.7% wheat bran + 15% glycerine + 5% yeast) on some demographic parameters of E. kuehniella. Moreover, the performance of the species Trichogramma evanescens Westwood reared on the E. kuehniella eggs reared on the 3 artificial diets were determined. For the E. kuehniella rearing, the CY diet had a higher fecundity and greater emergence ratios. Nevertheless, CY diet also provided shorter developmental time, greater fecundity, and relatively higher female ratios of subsequent generations of the parasitoids. Conclusion The results suggest that the CY diet could be considered as a standard diet for the multigenerational rearing of T. evanescens.