The mechanisms of resistance ofLeucaena collinsiiRose&Britton against the psyllidHeteropsylla cubanaCrawford were investigated by comparing the plant's response to the psyllid and the psyllid's behavioral and growth responses to the trees, usingLeucaena leucocephala(Lam.) de Wit as the susceptible control. Potted trees in the field were treated with fenvalerate to remove all insects. Four days later, the numbers of adults per shoot and the percentage of trees recolonized were 76–84 and 65% lower, respectively, forL. collinsiicompared withL. leucocephala. The numbers of eggs oviposited onL. collinsiiwere 46 and 63% lower than onL. leucocephalain field and laboratory experiments, respectively. There was also well over 90% reduction in adult eclosion, a smaller adult size and about 67% reduction in nymphal survival onL. collinsiithan onL. leucocephala. Premature leaflet senescence and abscission as well as intraspecific competition for feeding sites onL. collinsiimay have a severe effect on nymphal survival. These results disclose several mechanisms of antixenotic and antibiotic resistance that should be considered in resistance selection and breeding programs.