Interspecific competition for space between two hemipteran phytophagous insects associated with Myrtillocactus geometrizans (garambullo) and its consequences for their population structure

Abstract

Interspecific competition among insect herbivores is widely regarded as a significant selection pressure that impacts the distribution, abundance, and structure of their populations. Facilitator-mediated interactions, such as mutualism, have the capacity to modify the dynamics of competition. Furthermore, temporal fluctuations have been demonstrated to modify the outcome of competition. This study reanalyzes data on competition for space between two phytophagous insects commonly known as scales, namely Toumeyella martinezae Kondo and González (Hemiptera: Coccidae) and Opuntiaspis philococcus Cockerell (Hemiptera: Diaspididae), considering the presence or absence of Liometopum apiculatum Mayr (Hymenoptera: Formicidae) (a mutualistic ant species of T. martinezae) and the associated effects on their population structures. A total of 27 Myrtillocactus geometrizans (Mart. ex Pfeiff.) Console 1897 (Cactaceae) plants were selected for the study, with the presence of the study insects. The plants were then classified into one of five conditions: (1) O. philococcus in the absence of competition; (2) T. martinezae in conjunction with the mutualistic ant, L. apiculatum, in the absence of competition; (3) T. martinezae without competition; (4) T. martinezae and O. philococcus in competition, with the mutualistic ant; and (5) T. martinezae and O. philococcus in competition, without the mutualistic ant. A photographic record was maintained for a period of 6 months, during which the population structure was determined according to the size of each individual scale. The total abundance and relative space appropriation for each scale species were then estimated. The study revealed variations in spatial occupation over time. Toumeyella martinezae occupied more space during the initial months of the study, whereas O. philococcus predominated toward the termination of the study period. Competitive interaction significantly affected the population structure, changing over time and between species. In conclusion, the competitive dynamics changed over time, and the presence of the mutualistic ant had a significant effect, allowing the two competitors to coexist.