Does an increase in invertebrate biodiversity in rice fields affect rice water weevil (Lissorhoptrus oryzophilus) populations?

Rice IPM in the U.S. is done mainly with the use of pesticides, plant resistance and cultural practices, but lacks a biological control component.  Biological control is an important component of the management programs for many pests of Asian rice. Here we investigate whether increasing the diversity of aquatic invertebrates, by additions of composted manure, in a rice field can affect rice water weevil (Lissorhoptrus oryzophilus) populations. Treatments consisted of adding manure at the time of flooding to four plots and leaving the other four untreated; three weeks later, seeds were hand sown in all eight plots.  Control and manure-treated plots were kept continuously flooded for the season.  No insecticides were used in either treatment.  Plots were sampled by aquatic netting, trapping and floating pitfall traps.  Manure treatment did significantly increase biodiversity, affect L.oryzophilus numbers.  Increasing biodiversity in U.S. rice fields may be possible but further testing of detrital additions or other conservation biological control methods are needed.