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Research Project: Biological Control and Integrated Management of Invasive Arthropod Pests from Europe, Asia, and Africa

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Title: Development, survivorship and reproduction of Gryon aetherium Talamas (Hymenoptera: Scelionidae), an egg parasitoid of Bagrada hilaris (Burmeister) (Hemiptera: Pentatomidae), under eight constant temperatures


Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/3/2023
Publication Date: 2/8/2023
Citation: Martel, G., Sforza, R.F. 2023. Development, survivorship and reproduction of Gryon aetherium Talamas (Hymenoptera: Scelionidae), an egg parasitoid of Bagrada hilaris (Burmeister) (Hemiptera: Pentatomidae), under eight constant temperatures. Biological Control. 180.

Interpretive Summary: Bagrada bug or painted bug is reported as a pest of cole crops in its native range of eastern and southern Africa and the Indian subcontinent. In 2008, it was first reported in California, where it now attacks a wide range of Brassicaceae crops, including cabbage, broccoli, and radish. The bug has spread to New Mexico, Mexico, Hawaii, and Chile. To date, no efficient monitoring tools exist to long-term manage Bagrada bug populations in North America. The massive economic loss and the lack of alternative control practices, led U.S. growers to use broad-spectrum insecticides to reduce local pest populations. As new insecticides have been shown to be less effective on crucifer crops, a program on classical biological control based on foreign exploration in the native range has been initiated in 2016. Several parasitoid wasps of Bagrada were collected in Pakistan are now under investigation at USDA-ARS-EBCL, especially the egg parasitoid G. aetherium. The aim of the present study was to study in climatic chambers the thermal range of the Bagrada egg parasitoid for a possible establishment in USA. We assessed the effect of eight constant thermal regimes (from 15 to 40°C) on the parasitoid development, fecundity, longevity and demographic parameters. The parasitoid could reproduce under all tested temperature regimes, with the highest fecundity measured at 30 °C. Our results suggest that the Bagrada egg parasitoid would be able to establish and control bagrada in the warmest regions of USA, but would not provide promising control in crucifer crops of Californian coastal regions.

Technical Abstract: Environmental temperature is fundamental determinant of insect physiology and behavior, and the success of an importation biocontrol program often relies on the acclimatization capacity of the introduced biocontrol agent. Co-evolved natural enemies of a target pest that share the same climatic range are expected to be suitable candidates for introduction. The stink bug Bagrada hilaris (Burmeister) is an invasive pest in the USA which damages mainly brassica crops in California and other Southwest states. An egg parasitoid from Pakistan, Gryon aetherium Talamas (Hymenoptera: Scelionidae), is currently being evaluated as a classical biocontrol agent. In order to determine the range of temperatures suitable for G. aetherium, its development, reproduction and survivorship were evaluated in the laboratory under eight regimes of constant temperature, ranging from 15 to40 'C. Gryon aetherium was able to develop successfully between 18 'C (46.9 ± 0.6 d) and 37.5 'C (7.3 ± 0.09 d) with a maximum emergence rate of 95.5 ± 1.9 % at 25 'C. The parasitoid reproduced under all tested temperatures, with maximum fecundity at 30 'C (104.5 ± 21.2 progeny/female). The mean longevity of adult females was 151.3 ± 6.8 days at 15 'C and declined to 4.3 ± 0.3 days at 40 'C. Our results suggest that G. aetherium should establish in the warmest regions of USA, but would not likely control B. hilaris in crucifer crops of the Californian coastal regions where lower temperatures are likely to limit its developmental success.