Experimental field studies on predation and egg parasitism of rice brown planthopper in Indonesia
• Egg parasitism and general predation are known to be important mortality factors in the population dynamics of rice brown planthopper (BPH) Nilaparvata lugens in tropical Asia, but previous studies have not attempted to quantify and compare them.
• Field experiments in Java, Indonesia, are reported for 1993 and 1994. Plants previously infested with BPH eggs were put out in field cage-enclosures, which, by means of different size mesh gauze covering, allowed either: (1) free access to all natural enemies, (2) access only to egg parasitoids, or (3) no access to any natural enemies.
• After one BPH generation (30 days), numbers of adults and gravid females were counted for each treatment. In addition, plants were dissected to determine the numbers of eggs laid.
• An additional treatment in which all natural enemies were excluded, but lycosid spiders were added, was used in 1994 experiments in an attempt to assess the effects of predators in the absence of egg parasitoids.
• Numbers of BPH adults and eggs laid were highest when natural enemies were excluded and lowest when they had free access. Mortality due to egg parasitoids in the absence of predators was intermediate and significantly different to the two other treatments.
• The effects of added predators in the absence of egg parasitoids gave variable results, but again clearly demonstrated the significance of egg parasitism in overall BPH mortality.
• The conservation of BPH egg parasitoids should form an important element of any rice pest management programme in tropical Asia.