Contrasting Effects of the Invasive Hypogeococcus sp. (Hemiptera: Pseudococcidae) Infestation on Seed Germination of Pilosocereus royenii (Cactaceae), a Puerto Rican Native Cactus

Abstract We evaluated the impact of the Harrisia Cactus Mealybug (HCM), Hypogeococcus sp. (Hemiptera: Pseudococcidae), on seed germination of Pilosocereus royenii (Cactaceae) in Puerto Rico. Mature fruits were collected from individuals of P. royenii at various levels of HCM infestation, ranging from completely healthy plants to fruits growing directly on HCM-induced tumors. We hypothesized that germination will be directly and negatively affected by HCM infestation severity. After measuring germination and seedling survival for 160 days, we observed that seeds from fruits growing on tumors had the lowest germination rate compared to the other categories, as hypothesized. In addition, lightly infested plants germinated at a lesser rate compared to healthy plants, while seeds from severely infested plants germinated at a greater rate, contrasting with our hypothesis. We suggest that when the infestation is light, the host might be reallocating resources towards developing defensive responses. In contrast, when the infestation is severe, the host might be reallocating resources toward increasing germination.