1. The authors analysed the potential effects of interspecific competition on spatial distribution of two gall-inducing insects, Bystracoccus mataybae (Hemiptera: Eriococcidae) and Lopesia mataybae (Diptera: Cecidomyiidae), that co-occurring simultaneously in Matayba guianensis. Overall, the authors hypothesised that spatial gall distribution between and within leaflets is shaped by interspecific competition.2. The authors determine: i) the B. mataybae distribution between two different habitats; ii) the B. mataybae and L. mataybae distribution in the same habitat; and iii) the B. mataybae distribution when L. mataybae is present and absent in the habitat. For all experimental designs, the authors measured gall abundance along leaflet sizes, as well used a new Cartesian plane technique to map spatial gall distribution within the leaflet to obtain gall density.3. In Campo-cerrado, B. mataybae induced galls on small leaflets and in Cerrado on large leaflets, with similar spatial distribution within leaflets. Within the same habitat, B. mataybae induced galls on small leaflets, with higher gall density in the right basal of the blade, and L. mataybae on large leaflets, occupying the right apical area. In habitat with interspecific competition pressure (L. mataybae present), B. mataybae selected small leaflets with higher gall density on the right basal area, and in habitat without interspecific competition (L. mataybae absent), B. mataybae selected larger leaflets with broader distribution over within the blade.4. The study's findings confirm that both gall-inducing insect species diverge in their distribution, avoiding overlapping niches confirming that the spatial gall distribution of both gall-inducing species are driven by interspecific competition.

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