Why are corn planthoppers pests? Some answers and issues bordering in biodiversity, invasiveness, host resistance, etc.

Herbivores insects are mainly either chewing or piercing-sucking, with the other types generally perceived as more of exceptions than the rule. Hence, all plants whether in natural or man-made ecosystems, have their associated guilds of chewing and sucking herbivores. In corn, hoppers have gathered much of the limelight in recent months due to outbreaks of the corn planthopper (CPH), Stenocranus pacificus (Kirkaldy) (Delphacidae). Like most new pests and other problems that cause headaches to farmers, people always look for things or persons to blame and new crop varieties, whether products of conventional breeding or modern biotechnology, receive most of the accusing fingers. The need for scientific information to shed light in this controversy led to the conduct of these preliminary studies focusing mainly on field surveys in several areas in Luzon and Mindanao [Philippines] and on qualitative assessments of how varieties react to the new pest. Aside from S. pacificus, field collections revealed the presence of other hoppers (Hemiptera: Auchenorrhyncha: Fulgoromorpha) namely: Perigrinus maidis (Ashmead) (Delphacidae), Proutista moesta (Westwood) (Derbidae), Cicadulina bipunctata (Matsumura) (= C.bipunctella)(Cicadellidae), Cofana spectra (Distant) (Cicadellidae) and Ricania sp. (Ricaniidae). They have all been previously recorded on corn and all occur on all corn varieties observed in the field, and their distribution patterns are discussed. In addition to direct damage by sucking the plant sap, CPH also affects plant growth and development indirectly through the growth of sooty molds on the accumulated honeydew that they excrete. These sticky black molds also attract different organisms resulting in decreased photosynthesis and eventually stunted growth of the corn plants. There have been only few basic studies on the field resistance to CPH when it was first observed devastating vast corn production areas in Mindanao. Now it had reached several regions in Luzon [Philippines], it is imperative that adequate basic studies especially on its biology, ecology and behavior be given priority. There is no confirmed report on the specific resistance reaction of the different corn varieties in the field. However, based on preliminary assessments in the three areas, all varieties are attacked by the CPH, whether OPs, hybrids or genetically engineered hybrids. Basic ecological issues as to why insects become pests, the diversity of corn agroecosystems and surrounding vegetation including weeds, and related aspects in the systematics of arthropods are discussed especially in the light of CPH outbreaks and along the general subject of invasive alien arthropod species. Hypotheses and possible paths to finding solutions are offered.