The objective of this study was to determine the spatial patterns and associations of the South American fruit fly (Anastrepha fraterculus (Wiedemann);
Diptera: Tephritidae) and its parasitoids in organic orchards of common
guava and pineapple guava. The field study was conducted from Feb to
Mar 2010 in 2 organically-managed orchards, one of common guava (Psidium guajava L.) (Myrtaceae) and the other of pineapple guava [Acca sellowiana (O.
Berg) Burret] (Myrtaceae), in Rio Grande do Sul (RS) state, Brazil.
Fruits were sampled from all trees at 2 sampling occasions, spaced 15
days apart, just before fruits were in the final maturation period. On
each tree, 10 fruits were randomly collected from the entire canopy and
held in the laboratory until the flies had pupated. Heterogeneity of
insect count data was analyzed by fitting theoretical distributions to
the data and calculating dispersion indices. The spatial arrangement was
evaluated with SADIE. Local spatial associations were measured using a
SADIE association index (Ita). In a common guava orchard the emerged individuals were A. fraterculus, and its parasitoid, Doryctobracon areolatus (Szépligeti)
(Par) (Hymenoptera: Braconidae) with a parasitism rate of 8.3%. The
same 2 species occurred in a pineapple guava orchard, where the
parasitism rate was 25.5%. The variances of the data for both the A. fraterculus and D. areolatus were greater than the corresponding means for most cases, hence the significance of both the dispersion index (I) and the values of k of the negative binomial suggested an aggregated distribution pattern. On the other hand, the clustering indices (vi and vj) and Ita, suggested a random spatial pattern of A. fraterculus and
the parasitoid for most situations (orchards and sampling times).
Spatial association indices revealed significant associations for 5 of
the 12 pair-wise comparisons, 3 in the common guava orchard and 2 in the
pineapple guava orchard.