Insect biotypes and host plant resistance

Abstract

The green plants and herbivorous insects are engaged in a constant struggle for dominance. Humans usually intervene in this struggle by developing pest-resistant genotypes and other pest management tactics. Upon failure of a previously successful tactic to which the insect population has apparently adapted, the latter is often considered to be a novel or distinct entity and termed as a "biotype." The success of host plant resistance (HPR) strategy is constantly challenged by the occurrence of resistance-breaking insect biotypes. In general, the term "biotype" usually designates an intraspecific group of organisms that are not morphologically distinguishable, but differ by a biological function. Variation among individuals within populations has always been the focus of population genetics. However, the term "biotype" includes the entities that are not consistent either within or between biotypes, and their underlying genetic composition and origins, while generally unknown, are likely heterogeneous within and variable between biotypes. Biotypes may differ in some biological parameters, including detoxification pathways, reproductive rate, dispersal, virus vectoriality, and capacity to damage plants, and are well defined by microsatellite polymerase chain reaction (PCR)-based DNA markers. Insect biotypes feeding on different species of host plants are particularly well documented. To slow down the process of biotype selection, crop cultivars with broad genetic bases are needed. The durability of host plant resistance can be enhanced by identifying a wide array of potential insect-resistant genes and ensuring their incorporation in commercially important cultivars.