Nguyen Van Huynh and Nguyen Hong Lam
Can Tho University, Can Tho, Vietnam
The parasitization of BPH eggs in the field was recorded by using the BPH egg bait traps at the booting and ripening stages of the rice crop in Cai Be, Tien Giang province in the 2009-2010 dry crop season. Sample baits were placed in a set of fields that practiced ecological engineering and another set that did not use ecological engineering. Five species of egg parasitoids were identified from the bait traps 70.8% of the eggs were parasitized by Anagrus flaveolus (Mymaridae) and 17.0% by A. optapilis (Mymaridae) and 8.2% by Oligosita sp. (Trichogrammatidae).
Table 1 below shows that the average percentage of parasitized BPH eggs in the ecological engineering fields enriched with a diversity of flower species in the bunds were higher than those in control fields, both at 1 meter from the bunds and in the field centers, and at the booting and ripening stages. The parasitism rate was highest at the booting stage in the eco eng fields with average of 43-45%. From the literature about 29-91% of eggs parasitized can reduce the BPH (Claridge, 1999; 2002). Anagrus was the most common egg parasitoid at Tien Giang in the 1977-1978 survey with its parasitization fluctuating between 20 and 30% (Lam (2002). Anagrus flaveolus was also found to be the main parasitoid with less A. optapilis and Ologosita sp.(Lan et al., 2000).
The results thus confirm the importance of egg parasitism in managing BPH populations in and ecological engineering fields can lead to reduced vulnerability to BPH outbreaks. Yields of the ecological engineering fields were 6.9t/ha without any insecticide application. Further studies are needed for the selection of flower species that can contribution most to increasing parasitism and ecosystem services.
Table 1. Average percentage (%) of BPH eggs parasitized at the later stages of rice crop in the model field at Cái Bè (Tien Giang, Vietnam) monitored by the BPH eggs’ bait traps
|Rice field at developmental stage||One meter from the bund||At center|
|Eco Eng||45.95 ± 6.21||21.78 ± 3.37||43.59 ± 5.90||22.94 ± 2.19|
|Control||28.97 ± 3.67||13.07 ± 1.61||24.16 ± 2.82||10.55 ± 0.91|
a ns=non-significant, *= at 5% and **= at 1% significance.
In an earlier post Lan et al showed that parasitoid populations were higher in ecological engineering fields in Cai Be (Read: Parasitoid density higher). In Thailand Nalinee et al found that parasitoid species biodiversity was higher in ecological engineering fields (Read: Higher parasitoid biodiversity). Lu et al recorded higher natural enemy densities in ecological engineering fields grown with sesame in Jin Hua, China (Read: Higher natural enemies). It is consistent that ecological engineering with bunds populated with nectar rich plants and withholding insecticide sprays in the early crop stages would restore ecosystem services that parasitoids contribute and reduce crop vulnerability to pest outbreaks.
Claridge M.F., J.C. Morgan, A. E. Steenkiste, M. Iman and D. Damayanti. 1999. Seasonal patterns of egg parasitism and natural biological control of rice brown planthopper in Indonesia, Agricultural and Forest Entomology 1: 297-304.
Claridge M. F., J. C. Morgan, M. Iman and D. Damyanti. 2002. Experimental field studies on predation and egg parasitism of rice brown planthopper in Indonesia, Agricutural and Forest Entomology 4: 203-209.
Lan, L. P., N. P. D. Huyen, N. V. Cam, K. L. Heong and K. G. Schoenly. 2005. Species composition of arthropods in the rice field and its neighboring botanical ecosystems. Fifth National Conference in Entomology, Ha Noi, pp. 93-101 (In Vietnamese, English summary).
Lam, P. V. 2002. Natural Enemies of Insect Pests: Research and Application – Book I, Nong Nghiep Publ. house, Ha Noi, pp. 7-99 (In Vietnamese, English summary).