The beetle genus Diabrotica (corn rootworms) provides an excellent model to study the evolution of specialism versus generalism in the plants that insects can eat. The genus is divided into two distinct groups: Species in the virgifera group are specialists on maize and a few North American grasses. Fucata group species have a much broader range of suitable host plants. Furthermore, the genus includes some destructive and adaptable pests of agriculture. The western corn rootworm is a major maize pest, known as the “billion dollar bug” that has adapted to a variety of insecticides, cultural control methods and most recently genetically modified crops.

We first proposed sequencing the genome of the western corn rootworm over a decade ago and have been working on the genomics of the species ever since. The western corn rootworm genome was difficult to sequence because it is fairly large. At 2.6 billion basepairs, it is almost as large as the human genome. An active area of research in the lab is the patterns and causes of genome size evolution in Diabrotica.

Our lab was part of the team that sequenced and continues to analyze the western corn rootworm genome. Recently, the lab led the identification and analysis of genes encoding cytochrome P450 monooxygenases in the western corn rootworm genome sequence. We are also studying the genes involved adaptations to transgenic corn.

Another ongoing area of investigation is the relationship between Diabrotica species and DIMBOA, a defensive toxic chemical that is naturally produced by maize plants. Our lab and others have shown that while generalist feeding species from the fucata group tolerate DIMBOA, specialists from the virgifera group actually benefit from DIMBOA in their diet. We have identified two cytochrome P450 monoxygenase genes from western corn rootworm that appear to be induced by DIMBOA in the diet and are investigating the role of these genes, and the enzymes they encode, in the insect’s ability to tolerate and even take advantage of this toxin.