Tropical dry forests are threatened by invasive species. In Puerto Rican dry forests, two of these invasive species are the Harrisia cactus mealybug Hypogeococcus sp. (HCM), a member of the H. pungens-complex (Hemiptera: Pseudococcidae), and the liana Jasminum fluminense (Oleaceae). Here, we aim to determine the effects of HCM and J. fluminense on the flower and fruit production of Pilosocereus royenii and on the short-term mortality of the native columnar (P. royenii and Stenocereus fimbriatus), semi-epiphytic (Selenicereus trigonus and Leptocereus quadricostatus), and globular (Melocactus intortus) cacti of Puerto Rico. To assess HCM infestation, we created a numerical infestation index with six categories, ranging from uninfested and healthy, to heavily infested cacti (0–5) based on the number and size of tumors. Flower and fruit production of P. royenii was observed at three sites, while the survival of all cactus species was observed at twelve sites for 2 years. Mortality of all cacti species increased with severe HCM infestation. Mortality was highest in M. intortus, and lowest in St. fimbriatus and L. quadricostatus. Mortality of P. royenii was negatively correlated to precipitation, and positively to HCM and liana infestation. Individuals of P. royenii that were heavily infested with both HCM and lianas were more likely to die than healthy cacti only infested with lianas, while P. royenii flower and fruit production was negatively correlated only with HCM infestation. This suggests that J. fluminense becomes a better competitor during dry periods when P. royenii is infested with HCM. While other members of the H. pungens-complex are considered biocontrol agents in places where columnar cacti are not native, this study demonstrates that HCM species found in Puerto Rican dry forests could potentially decrease the biodiversity of these cacti in their native habitats.