Letourmy, P.

Mze Hassani, I.

Naudin, K.

Rabary, B.

English

Wageningen Yield 

5
th
 World Congress of Conservation Agriculture incorporating 3
rd
 Farming Systems Design Conference, September 2011 Brisbane, 
Australia www.wcca2011.org 
149 
White grubs, Scarabaeidae larvae (Insecta, Coleoptera) control by plants in Conservation Agriculture: effects 
on macrofauna diversity 
 
Rabary B
1
, Naudin K
2
, Letourmy P
2
, Mze Hassani I
3
, Randriamanantsoa R
1
, Michellon R
2
, Rafarasoa L
3
, Ratnadass A
2
 
1
FOFIFA URP Systèmes de Culture et Rizicultures durables. BP 230 Antsirabe 110, Madagascar; bodo.rabary@gmail.com 
2
 CIRAD UPR SCA, UPR URSIA and UPR HortSys, 34398 Montpellier France 
3Université d‘Antananarivo, Antananarivo 110, Madagascar 
 
Keywords: rice-based cropping system, direct seeding, cover crop, Madagascar 
 
Introduction 
Adoption of conservation tillage has reduced soil erosion in many parts of the world. Conservation management practices improve soil 
quality through the significant amounts of organic residues left on the soil surface, and cover crops also provide many benefits. These 
supply residues derived from dead plant parts and organic substances released from their living roots, and may foster soil organisms‘ 
abundance and diversity. They may also enhance ecosystem functions such as nutrient cycling (Rabary et al., 2008), soil structure and C 
sequestration, and pest and disease control (Ratnadass et al., 2006). In some regions of Madagascar, white grubs were found to be more 
abundant under direct seeding mulch based cropping systems (Ratnadass et al., 2006). White grubs are C-shaped larvae of a large group of 
beetles (Coleoptera:Scarabaeidae). Several species in this group cause significant damage to cereal crops by feeding on plant roots. The 
entomopathogenic bacterium Metarhizium anisopliae has been proven effective in controlling white grubs in some cases (Razafindrakoto et 
al., 2010), However, Randriamanantsoa et al. (2010) showed that there are many species of white grubs in Madagascar and most of them 
are endemic. Furthermore, some species are not pests but show "soil engineering" behaviour. This wide array of white grub species makes 
their biological control difficult. The fundamental dilemma in pest control with insecticide application is about significant detrimental 
effects on non-target species in the food web, which may deplete soil diversity and increase the possibility for subsequent pest outbreaks. 
This paper reports the impact a number of cover crops known for their pest-suppressing on white grub control within upland rice cropping 
systems. We presumed that these plants toxicity would alter the composition of soil macrofauna, but not negatively affect biodiversity 
overall, due to the positive effects of cover crops compared to those of the conventional tillage system. 
 
Materials and Methods 
A field experiment was conducted in 2009-10 in the Highlands of Madagascar, in the district of Andranomanelatra (S 19°46‘45‖, E 
47°06‘25‖), Antsirabe region. The area has a cold tropical upland climate with 10 – 20 days of frost annually and a mean temperature of 
16.9°C. The site is at 1600 m above sea level with an annual average rainfall of 1450 mm. The soil is an andic distrustept, pH (H2O) 5.4. 
The experiment was set up in a randomized complete block (RCB) design with 48 plots in 8 treatments over 6 blocks. Plot size was 14 m x 
9 m. The treatments within rice-based cropping systems were no-tillage (NT) with cover crops compared to sole rice under NT without 
cover crop and rice under conventional tillage (CT). The cover crops used for white grub control were: hairy vetch (Vicia villosa), fodder 
radish (Raphanus sativus), Brachiaria ruziziensis x B. brizantha (var. mulato), Crotalaria grahamiana, Cleome hirta, Tagetes minuta and 
Cosmos caudatus. The 8 treatments were: i) Rice-Brachiaria; ii) Rice-Cleome-Tagetes-Cosmos; iii) Rice- Crotalaria; iv) Rice-Vetch; v) 
Rice-Radish; vi) Rice-Bean NT; vii) Rice-Bean CT; viii) sole Rice. In 2010, soil macrofauna abundance and diversity were assessed within 
each plot. One soil monolith, 25 cm x 25 cm x 30 cm, was extracted per plot, separated into litter and three layers: 0-10 cm, 10-20 cm, and 
20-30 cm in depth according to the TSBF method. Monoliths were hand-sorted to collect invertebrates larger than 2 mm. Soil macrofauna 
were identified, counted and weighed. ANOVA were performed, using SAS (proc glm), on data transformed for non-parametric tests based 
on ranks according to Conover (1999). LSD test at P < 0.05 was performed to assess the differences among the means of abundance and 
biomass of macrofauna groups of six replicates. 
 
Results and Discussions 
In 2010, 2,155 individuals were collected from all the plots, counted and classified into 20 Orders and 48 Families. Classification were 
done up to species when possible but many species were not identified. The highest taxa numbers were found under Raphanus sativus and 
Vicia villosa (respectively 31 and 30 Families), with the lowest under CT and sole rice (19 and 20 Families). The NT system increased taxa 
number by 12% based on the rice + beans NT and rice + beans CT comparison. The NT increased taxa number by 16% under Brachiaria 
and Crotalaria cover crops. It increased up to 25% under radish. In decreasing order of abundance, the major taxa present in soil monoliths 
were Hymenoptera (ants) 32%, Haplotaxida (earthworm, mainly Pontoscolex corethrurus) 23% and Coleoptera 21%. All the other taxa 
accounted for less than 3% each, giving 24% in total. As for the feeding strategy (Table 1), there were no significant differences of 
macrofauna abundance in each group except for detritiphagous. Sole rice had the lowest number of detritiphagous although this was under 
NT system. Even so, it had no significant difference from the rice-bean NT. Sole rice NT also had poor macrofauna diversity. Our results 
confirm the importance of cover crops, especially under NT.  They improve soil microclimatic conditions such as temperature, moisture 
and physical habitat. Moreover, the soil enrichment by organic matter from these plants favoured detritiphagous activity. Concerning 
macrofauna biomass, there were significant differences between cropping systems only for phytophagous and the non-identified group. The 
lowest phytophagous biomass means were found under rice-bean CT and rice-radish NT. White grubs formed 7.7% of the macrofauna 
density and the non-pest species were dominant (Table 2). White grub pests were absent from only three cropping systems (rice-bean CT, 
sole rice and rice-radish), while they were found in highest numbers under Brachiaria and Vetch. The significant soil pest attack observed 
in the sole rice field suggests damage by adults (data not shown) or other pest species. There is therefore a need to identify all white grub 
species, of which many are endemic. We also found Polycleis africanus (Curculionidae) was an important pest in some systems. Radish 
seems promising for white grub pest control. In addition, it did not reduce macrofauna diversity and abundance. Vetch was also favourable 
for macrofauna abundance but it did not express white grub pest control potential.  Our results emphasise the importance of studying a 
wide range of plants as cover crops or residue mulch for soil pest control and the need to explore more plant species, because some have 
specific pest-suppressive effects.  
 
References 
Conover WJ 1999 Practical nonparametric statistics, 3rd edn,Wiley, New York. 
Rabary B, Sall S, Letourmy P, Husson O, Ralambofetra  E, Moussa N, Chotte JL 2008 Effects of living mulches or residue amendments on 
soil microbial properties in direct seeded cropping systems of Madagascar, Applied Soil Ecology, 39, 236-243. 
5
th
 World Congress of Conservation Agriculture incorporating 3
rd
 Farming Systems Design Conference, September 2011 Brisbane, 
Australia www.wcca2011.org 
150 
Randriamanantsoa R, Aberlenc HP, Ralisoa OB, Ratnadass A, Vercambre B 2010 Les larves des Scarabaeoidea (Insecta, Coleoptera) en 
riziculture pluviale des régions de haute et moyenne altitudes du Centre de Madagascar, Zoosystema, 32, 19-72. 
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Pretty, P Sanchez, N Sanginga and J Thies, CRC Press-Taylor and Francis, Boca Raton, Florida, pp. 589-602. 
Razafindrakoto RC, Rakotoarisoa HL, Razafindrakotomamonjy A, Ratnadass A, Vercambre B 2010 Lutte biologique intégrée contre des 
insectes terricoles, Heteronychus spp à Madagascar, par un champignon entomopathogène sur riz pluvial en semis direct sous 
couverture végétale, Etude et Gestion des Sols, 17, 2, 159-168. 
 
 
  


Effects of soil and plant management on crop pests and diseases‘ , in Biological Approaches to Sustainable Soil Systems,

Lutte biologique intégrée contre des insectes terricoles, Heteronychus spp à Madagascar, par un champignon entomopathogène sur riz pluvial en semis direct sous couverture végétale,

Practical nonparametric statistics, 3rd edn,Wiley,

White grubs, Scarabaeidae larvae (Insecta, Coleoptera) control by plants in conservation agriculture: effects on macrofauna diversity

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White grubs, Scarabaeidae larvae (Insecta, Coleoptera) control by plants in conservation agriculture: effects on macrofauna diversity

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