Common Agricultural Pest Research Articles

Comment on "A Keystone Mutualism Drives Pattern in a Power Function"

Vandermeer and Perfecto (Reports, 17 February 2006, p. 1000) reported a general power law pattern in the distribution of a common agricultural pest. However, there is an exact analytical solution for the expected cluster distribution under the proposed null model of density-independent growth in a patchy landscape. Reanalysis of the data shows that the system is not in a critical state but confirms the importance of a mutualism.

A Keystone Mutualism Drives Pattern in a Power Function

Data that can be described by a power function are ubiquitous in nature. Although there is consensus that such data frequently emerge generally from nonlinear complex systems, a variety of specific mechanisms may be responsible for creating the pattern in particular cases. Here, we report on the distribution of a scale insect (Coccus viridis) that is a common agricultural pest. Its distribution in an organic coffee farm in southern Mexico generally follows a power function, but there are subtle deviations from that function. We offer a biological explanation for both adherence to the power functions and associated deviations, along with supporting evidence.

Reticulate evolution and the origins of ribosomal internal transcribed spacer diversity in apomictic Meloidogyne.

Among root knot nematodes of the genus Meloidogyne, the polyploid obligate mitotic parthenogens M. arenaria, M. javanica, and M. incognita are widespread and common agricultural pests. Although these named forms are distinguishable by closely related mitochondrial DNA (mtDNA) haplotypes, detailed sequence analyses of internal transcribed spacers (ITSs) of nuclear ribosomal genes reveal extremely high diversity, even within individual nematodes. This ITS diversity is broadly structured into two very different groups that are 12%-18% divergent: one with low diversity (< 1.0%) and one with high diversity (6%-7%). In both of these groups, identical sequences can be found within individual nematodes of different mtDNA haplotypes (i.e., among species). Analysis of genetic variance indicates that more than 90% of ITS diversity can be found within an individual nematode, with small but statistically significant (5%-10%; P < 0.05) variance distributed among mtDNA lineages. The evolutionarily distinct parthenogen M. hapla shows a similar pattern of ITS diversity, with two divergent groups of ITSs within each individual. In contrast, two diploid amphimictic species have only one lineage of ITSs with low diversity (< 0.2%). The presence of divergent lineages of rDNA in the apomictic taxa is unlikely to be due to differences among pseudogenes. Instead, we suggest that the diversity of ITSs in M. arenaria, M. javanica, and M. incognita is due to hybrid origins from closely related females (as inferred from mtDNA) and combinations of more diverse paternal lineages.