Development of an aqueous xanthan-guar gum spray solution suitable for mechanised release of Trichogramma ostriniae (Hymenoptera: Trichogramma) parasitised host eggs

• Published in: Biocontrol science and technology Vol. 35; no. 9; pp. 1003 - 1025
• Main Authors: Dionne, Ariane, Khelifi, Mohamed, Todorova, Silvia
• Format: Journal Article
• Language: English
• Published: Abingdon Taylor & Francis 02.09.2025; Taylor & Francis Ltd
• Subjects: Adjuvants; Bentonite; biocontrol technique; Cereal crops; Eggs; Guar gum; Gums; Injection systems; Locust bean gum; mechanised release; Ostrinia nubilalis; rainfastness; spray solution; Spraying; Sweetcorn; Trichogramma; Trichogramma ostriniae; Xanthan
• ISSN: 0958-3157; 1360-0478
• DOI: 10.1080/09583157.2025.2533837

In sweet corn crops, large fields must be protected against its main pest: Ostrinia nubilalis. In this context, an innovative spraying approach allowing the introduction of Trichogramma has been developed. However, its efficacy is highly dependent on the quality of its spraying solution. This study investigated the concentrations and the ratios between xanthan and guar gums that will generate adequate viscosity for the suspension of T. ostriniae parasitised host eggs under the temperature and stress conditions intrinsic to the spraying method to ultimately limit the total quantity of gums. Laboratory drip tests allowed exploring the improvement in rainfastness of the spray solution mixed with adjuvants (locust bean gum, molasses, skimmed milk, and bentonite). Finally, the emergence rate of T. ostriniae mixed in the xanthan-guar gum solutions with the most promising adjuvants was investigated. Major finding was that droplet size affected the most the emergence rate as volumes of 0.1 to 1 mL were detrimental to the survival of Trichogramma. Moreover, the drip test revealed that solution 11 (0.15%, 3:1) with bentonite at 4 g/L highly improved the rainfastness while 2 g/L of bentonite resulted in a better emergence with a reduction of 11.94% compared to the control treatment. This research has therefore established the favourable criteria for the spraying solution of Trichogramma parasitised host eggs and recommends the use of an injection system combining high xanthan-guar gum concentration for parasitised host eggs suspension, 4 g/L (1:1), and diluted xanthan-guar gum concentration, 1.5 g/L (1:1), during spraying to improve the Trichogramma spraying technique.