The Harrisia Cactus Mealybug (HCM), Hypogeococcus pungens, is a pseudococcid (Hemiptera) that represents an aggressive invader in the Caribbean. It threatens Pilosocereus royenii, a native columnar cactus and the most common cacti in Puerto Rico. In fact, deformed and possibly infertile flowers had been observed growing on gall growth after the infestation by HCM. This research was conducted to determine the effect of different severities of HCM infestation on the flower and fruit set, and reproductive phenology of P. royenii. The research was conducted in Cabo Rojo Wildlife and Fisheries Refuge in Puerto Rico. Three plots were set (LA, JR and CR) and surveyed with an infestation index 0-5, created by the amount of galls and their sizes. Each cacti was evaluated and assigned to one of the categories if it presented at least three or more symptoms included in the category. Only cacti taller than 0.75m were considered in this study as reproductively mature, and used to determinate the phenology of flowering and fruitification. Six visits were done to CR and LA and four to JR through a 14 months, from October 2014 to January 2016. Flowers and fruits were counted on all stages during all the visits, while the index and height were determined only during the first visit.
The total number of flowers and fruits significantly varies between infestation index, with healthy or not-infested cacti producing a higher number of fruits and flowers than infested cacti with an index of two or higher. This implies that light severities infestation resulted in little effects on the fruit and flower sets of P. royenii, while medium and severe infestations resulted in a reduction in these reproductive sets. Therefore, the reproductive phenology was conserved on all severities levels, but with different flower and fruit set. Then, this represents a difficulty in the reproduction rate of the specie, since it is a plant dependent on pollinators for its fertilization, both invertebrate and vertebrate pollinators. It is important to attest that the cacti species represents a source of food and shelter for other organisms in the arid ecosystems of the island. So that, the species conservation is necessary to maintain the ecosystems functions and wellbeing.