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Nitrogen improves ecological fitness of Cyrtorhinus lividipennis, but weakens its predation efficiency on the brown planthopper

Brown planthoppers (BPH) insert their eggs into the leaf sheaths to avoid mortality. Thus only very few natural enemies can attack them. In rice ecosystems, there are however two groups that have adapted and can access the BPH eggs and they are the egg parasitoids and the mirid egg predator, Cyrtorhinus lividipennis.

by Moni on May 27, 2013

by
Lu Zhongxian,  Zheng Xusong, Xu Hongxing, Institute of Plant Protection and Microbiology, Zhejiang Academy of Agricultural Sciences, Hangzhou 310021, China,
S. Villareal, K.L. Heong, International Rice Research Institute, Los Baños, Philippines

Cyrtorhinus lividipennis and illustration of the feeding mouth parts probing into rice plants to feed on BPH eggs

 

Brown planthoppers (BPH) insert their eggs into the leaf sheaths to avoid mortality. Thus only very few natural enemies can attack them. In rice ecosystems, there are however two groups that have adapted and can access the BPH eggs and they are the egg parasitoids and the mirid egg predator, Cyrtorhinus lividipennis. The mirid egg predator has specialized sucking mouth parts that can pierce into the BPH eggs and suck up its content thus killing the BPH before it is hatched. Besides feeding on planthopper eggs, the predator also feeds on young nymphs of planthoppers  and plant tissues.

 

High nitrogen content in plants has been known to increase planthopper fitness (Lu and Heong 2009).  Similarly nitrogen-enriched crops seem to increase the egg predator as well. Cyrtorhinus females lived longer and laid more eggs when reared on rice plants with higher nitrogen content.

 

Figure 1: Longevity and egg oviposition of Cyrtorhinus reared on plants with increasing nitrogen contents

 

However,  in functional response experiments to quantify predation we found that Cyrtorhinus had weaker attack rates in high nitrogen plant arenas.  Searching efficiency, estimated using Rogers’ Random Predator model, was found to be 0.13 and 0.28 in 200N plants and 0N plants, respectively.  Handling time or time the insect spent not searching was estimated to be about 11% higher in 200N plants than in 0N plants (20 and 18 minutes, respectively). This was probably because of the predator’s preference to feed on eggs inserted in the leaf blades rather than the leaf sheaths.

Figure 2: BPH consumed by Cyrtorhinus inserted in leaf blades and leaf sheaths

The full paper has been submitted for publication in Biological Control.

 

Reference

 

Lu, Z.X. and Heong, K.L., 2009. Effects of nitrogen-enriched rice plants on ecological fitness of planthoppers. In: Heong KL, Hardy B, (Ed.), Planthoppers: new threats to the sustainability of intensive rice production systems in Asia. Los Baños (Philippines):International Rice Research Institute. pp. 247-256.

 

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