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In the summer of 2023, ingestion of Astylus atromaculatus (pollen beetle) was linked to spontaneous fatal disease in grazing cattle and sheep in Argentina and Uruguay. While the disease was experimentally reproduced in sheep and guinea pigs in the 1970's, no experimental reproductions have been attempted in cattle, and controversy exists as to whether this insect is indeed noxious to cattle and at which dose. Here, we demonstrate that A. atromaculatus causes acute fatal disease in Hereford calves at single oral dosages of 2.5, 4.5, 10.0, and 15.0 g of insect/kg body weight. Death or severe disease necessitating euthanasia occurred at 38 to 48 hours postinoculation regardless of the dose, suggesting that the single fatal dosage is likely <2.5 g/kg body weight (this dose representing approximately 850 mL of intact beetles in a 100 kg calf). Clinically, the disease was characterized by acute anorexia, prolonged recumbency, reluctance to move, listlessness/apathy, depression, ruminal hypomotility and tympany, hypothermia, bruxism with frothing at the mouth, and mucoid diarrhea progressing to death. Hematologic and biochemical alterations included hemoconcentration, stress/acute inflammatory leukogram, negative energy balance, and ketosis. The pathological hallmark of this experimental disease is acute necrotizing omaso-reticulo-rumenitis, fibrinohemorrhagic enteritis, and exfoliative colitis with intralesional chitinous insect fragments. While A. atromaculatus might contain a gastrointestinal toxin or pathogen, extensive toxicological testing failed to identify a causative toxin. Other pathomechanisms such as direct physical damage caused by insect fragments on the alimentary tract seem plausible, although further studies are needed to elucidate the pathogenesis of A. atromaculatus -associated disease. [ABSTRACT FROM AUTHOR]

Simple Summary: Exotic water primroses (Ludwigia spp.) are aggressive plant invaders in aquatic ecosystems worldwide. Management of exotic Ludwigia spp. is limited to physical and chemical control methods. Biological control, the use of insects to control exotic plants, is an alternative approach for the management of exotic Ludwigia spp. However, little is known regarding the natural enemies of these plants in their native range in South America. In this study, we investigated the biology and host range of a natural enemy, the flea beetle Lysathia flavipes, to determine its suitability as a biocontrol agent for exotic Ludwigia spp. in the USA. The beetle matures from egg to adult in approximately 20 days at 25 °C. Females lived approximately 86 days and laid 278–2456 eggs over their lifespans. No-choice development and oviposition tests were conducted using four exotic Ludwigia species and seven native USA plant species. The beetle showed little discrimination between plant species: larvae aggressively fed and completed development, and females laid eggs on most plant species regardless of origin. These results indicate that the beetle is not sufficiently host-specific for further consideration as a biological control agent of exotic Ludwigia spp. in the USA and further testing is not warranted. Exotic water primroses (Ludwigia spp.) are aggressive invaders in aquatic ecosystems worldwide. To date, management of exotic Ludwigia spp. has been limited to physical and chemical control methods. Biological control provides an alternative approach for the management of invasive Ludwigia spp. but little is known regarding the natural enemies of these exotic plants. Herein the biology and host range of Lysathia flavipes (Boheman), a herbivorous beetle associated with Ludwigia spp. in Argentina and Uruguay, was studied to determine its suitability as a biocontrol agent for multiple closely related target weeds in the USA. The beetle matures from egg to adult in 19.9 ± 1.4 days at 25 °C; females lived 86.3 ± 35.6 days and laid 1510.6 ± 543.4 eggs over their lifespans. No-choice development and oviposition tests were conducted using four Ludwigia species and seven native plant species. Lysathia flavipes showed little discrimination between plant species: larvae aggressively fed and completed development, and the resulting females (F1 generation) oviposited viable eggs on most plant species regardless of origin. These results indicate that L. flavipes is not sufficiently host-specific for further consideration as a biocontrol agent of exotic Ludwigia spp. in the USA and further testing is not warranted. [ABSTRACT FROM AUTHOR]