all sites were situated in the communes of lo , boura , and biha , within a radius of 30  km from the city of lo ( 11.10 n , 02.10 w ) .
the climate is characterized by a unimodal rainfall pattern , with the rainy season starting in may and ending in october .
the work was carried out at farmers fields and hedges of j. curcas , planted between 2009 and 2012 . to study the population dynamics of a. whitfieldi over a year s time ,
12 sites planted in 2009 were selected in the communes of lo and biha . in each commune ,
two monocultures of j. curcas , two fields where j. curcas was intercropped with various other crops , and two j. curcas hedges were monitored from 1012 september 2012 to 24 september 2013 in lo and biha , respectively . in the intercropping systems ,
planting distances for j. curcas was 2 by 2 by 8  m , i.e. , two rows of j. curcas were planted at 2  m distance and at 8  m from two other rows .
other crops were usually planted at 1.3  m distance from j. curcas stems . intercropped plants included soybean , maize , groundnut , okra or pepper , and the species varied among fields and seasons .
every week , five trees were selected haphazardly in each plantation and the number of a. whitfieldi found on each tree was counted .
tree size varied within and between plantations because trees were growing rapidly and were pruned by the farmers .
however , there was no evidence of significant differences in tree size among plantation systems throughout the year of observation . the monitoring system for assessing the population dynamics in the 12 plantations described earlier was also used to compare abundance of a. whitfieldi in monocultures , intercropped fields , and hedges
however , because of the low number of plantations involved in this study , another study to assess environmental factors influencing the abundance of a. whitfieldi was carried out from 19 september to 1 october 2012 . at that time , a. whitfieldi was present at various levels of infestation in all plantations of the region .
thirty - one plantations were chosen haphazardly in the communes of lo , boura , and biha and surveyed for a. whitfieldi : 10 hedges , 13 monoculture fields of j. curcas , and 8 fields where j. curcas was intercropped with other plants .
all fields were first planted in 2009 or 2010 , but in many cases , young seedlings were planted later to replace dead trees . in each plantation , 20 trees of at least 2-yr old ( i.e. , planted in 2009 or 2010 ) were randomly selected . for each tree , damage by a. whitfieldi was assessed only in the lower part of the tree ( 50  cm from the soil ) to minimize the effect of tree size , taking into account that trees had different heights and damage is usually higher in the lower part of the crown .
damage was assessed by evaluating , on 10 leaves , the average surface of leaves with damage by a. whitfieldi , i.e. , the surface where photosynthesis can not be performed , whether by direct feeding or drying out of the leaf due to the insect pest .
instead , we scored the average attack as follows : < 1% ( average 0.5% ) of leaf surface damaged ; 15% ( average 3% ) ; 520% ( average 12.5% ) ; 2050% ( average 30% ) ; 5090% ( average 70% ) ; and > 90% ( average 95% ) . to score the general level of infestation of a plantation
, we averaged all the average percentages of infestation of the 20 trees . at each plantation
, we also assessed the proximity with fallow lands , i.e. , we noted whether fields and hedges were directly adjacent to fallow lands or only to cultivated lands ( i.e. , where all assessed trees were at least 100  m from the next fallow ) . for fields , we also noted whether the field itself was left as fallow or weeded . when the field was not weeded , we considered it as a fallow . to further assess the influence of the distance to fallow lands on damage , in september 2012 we chose a field with 3-mo - old plants , weeded and intercropped with soybean , adjacent to fallow land at only one side , the three other sides being occupied by various weeded crops .
we assessed the level of infestation , using the same scale , of five randomly selected trees at 1 , 6 , 11 , 16 , 22 , 28 , 33 , 38 , 43 , and 48  m from the fallow land . to compare the abundance of a. whitfieldi between the three cropping systems at the 12 sites where beetle populations were monitored during 1 yr , we used a linear mixed effects model with cropping system as fixed factor , village as random factor , and the sum of beetle number per field as dependent variable . to analyze the influence of cropping systems and environmental factors on the level of infestation by a. whitfieldi at the 31 plantations monitored in september 2012
fixed factors used were j. curcas as hedge versus fields ( all data ) ; monoculture versus intercropping ( fields only ) ; and j. curcas plants adjacent to fallows in or outside the fields ( all data and fields only ) . in the 3-month - old j. curcas field adjacent to fallow lands
, the relationship between the level of infestation by the beetle and the distance to the nearest fallow was analyzed using a pearson correlation .
all sites were situated in the communes of lo , boura , and biha , within a radius of 30  km from the city of lo ( 11.10 n , 02.10 w ) .
the climate is characterized by a unimodal rainfall pattern , with the rainy season starting in may and ending in october .
the work was carried out at farmers fields and hedges of j. curcas , planted between 2009 and 2012 . to study the population dynamics of a. whitfieldi over a year s time ,
12 sites planted in 2009 were selected in the communes of lo and biha . in each commune ,
two monocultures of j. curcas , two fields where j. curcas was intercropped with various other crops , and two j. curcas hedges were monitored from 1012 september 2012 to 24 september 2013 in lo and biha , respectively . in the intercropping systems ,
planting distances for j. curcas was 2 by 2 by 8  m , i.e. , two rows of j. curcas were planted at 2  m distance and at 8  m from two other rows .
other crops were usually planted at 1.3  m distance from j. curcas stems . intercropped plants included soybean , maize , groundnut , okra or pepper , and the species varied among fields and seasons .
every week , five trees were selected haphazardly in each plantation and the number of a. whitfieldi found on each tree was counted .
tree size varied within and between plantations because trees were growing rapidly and were pruned by the farmers .
however , there was no evidence of significant differences in tree size among plantation systems throughout the year of observation . the monitoring system for assessing the population dynamics in the 12 plantations described earlier was also used to compare abundance of a. whitfieldi in monocultures , intercropped fields , and hedges
however , because of the low number of plantations involved in this study , another study to assess environmental factors influencing the abundance of a. whitfieldi was carried out from 19 september to 1 october 2012 . at that time , a. whitfieldi was present at various levels of infestation in all plantations of the region .
thirty - one plantations were chosen haphazardly in the communes of lo , boura , and biha and surveyed for a. whitfieldi : 10 hedges , 13 monoculture fields of j. curcas , and 8 fields where j. curcas was intercropped with other plants .
all fields were first planted in 2009 or 2010 , but in many cases , young seedlings were planted later to replace dead trees . in each plantation , 20 trees of at least 2-yr old ( i.e. , planted in 2009 or 2010 ) were randomly selected . for each tree , damage by a. whitfieldi was assessed only in the lower part of the tree ( 50  cm from the soil ) to minimize the effect of tree size , taking into account that trees had different heights and damage is usually higher in the lower part of the crown .
damage was assessed by evaluating , on 10 leaves , the average surface of leaves with damage by a. whitfieldi , i.e. , the surface where photosynthesis can not be performed , whether by direct feeding or drying out of the leaf due to the insect pest .
instead , we scored the average attack as follows : < 1% ( average 0.5% ) of leaf surface damaged ; 15% ( average 3% ) ; 520% ( average 12.5% ) ; 2050% ( average 30% ) ; 5090% ( average 70% ) ; and > 90% ( average 95% ) . to score the general level of infestation of a plantation
, we averaged all the average percentages of infestation of the 20 trees . at each plantation
, we also assessed the proximity with fallow lands , i.e. , we noted whether fields and hedges were directly adjacent to fallow lands or only to cultivated lands ( i.e. , where all assessed trees were at least 100  m from the next fallow ) . for fields , we also noted whether the field itself was left as fallow or weeded . when the field was not weeded , we considered it as a fallow . to further assess the influence of the distance to fallow lands on damage , in september 2012 we chose a field with 3-mo - old plants , weeded and intercropped with soybean , adjacent to fallow land at only one side , the three other sides being occupied by various weeded crops .
we assessed the level of infestation , using the same scale , of five randomly selected trees at 1 , 6 , 11 , 16 , 22 , 28 , 33 , 38 , 43 , and 48  m from the fallow land . to compare the abundance of a. whitfieldi between the three cropping systems at the 12 sites where beetle populations were monitored during 1 yr , we used a linear mixed effects model with cropping system as fixed factor , village as random factor , and the sum of beetle number per field as dependent variable . to analyze the influence of cropping systems and environmental factors on the level of infestation by a. whitfieldi at the 31 plantations monitored in september 2012
fixed factors used were j. curcas as hedge versus fields ( all data ) ; monoculture versus intercropping ( fields only ) ; and j. curcas plants adjacent to fallows in or outside the fields ( all data and fields only ) . in the 3-month - old j. curcas field adjacent to fallow lands
, the relationship between the level of infestation by the beetle and the distance to the nearest fallow was analyzed using a pearson correlation .
all sites were situated in the communes of lo , boura , and biha , within a radius of 30  km from the city of lo ( 11.10 n , 02.10 w ) .
the climate is characterized by a unimodal rainfall pattern , with the rainy season starting in may and ending in october .
the work was carried out at farmers fields and hedges of j. curcas , planted between 2009 and 2012 .
to study the population dynamics of a. whitfieldi over a year s time , 12 sites planted in 2009 were selected in the communes of lo and biha . in each commune ,
two monocultures of j. curcas , two fields where j. curcas was intercropped with various other crops , and two j. curcas hedges were monitored from 1012 september 2012 to 24 september 2013 in lo and biha , respectively . in the intercropping systems ,
planting distances for j. curcas was 2 by 2 by 8  m , i.e. , two rows of j. curcas were planted at 2  m distance and at 8  m from two other rows .
other crops were usually planted at 1.3  m distance from j. curcas stems . intercropped plants included soybean , maize , groundnut , okra or pepper , and the species varied among fields and seasons . every week
, five trees were selected haphazardly in each plantation and the number of a. whitfieldi found on each tree was counted .
tree size varied within and between plantations because trees were growing rapidly and were pruned by the farmers .
however , there was no evidence of significant differences in tree size among plantation systems throughout the year of observation .
the monitoring system for assessing the population dynamics in the 12 plantations described earlier was also used to compare abundance of a. whitfieldi in monocultures , intercropped fields , and hedges . however , because of the low number of plantations involved in this study , another study to assess environmental factors influencing the abundance of a. whitfieldi was carried out from 19 september to 1 october 2012 . at that time , a. whitfieldi was present at various levels of infestation in all plantations of the region .
thirty - one plantations were chosen haphazardly in the communes of lo , boura , and biha and surveyed for a. whitfieldi : 10 hedges , 13 monoculture fields of j. curcas , and 8 fields where j. curcas was intercropped with other plants .
all fields were first planted in 2009 or 2010 , but in many cases , young seedlings were planted later to replace dead trees . in each plantation , 20 trees of at least 2-yr old ( i.e. , planted in 2009 or 2010 ) were randomly selected . for each tree , damage by a. whitfieldi was assessed only in the lower part of the tree ( 50  cm from the soil ) to minimize the effect of tree size , taking into account that trees had different heights and damage is usually higher in the lower part of the crown .
damage was assessed by evaluating , on 10 leaves , the average surface of leaves with damage by a. whitfieldi , i.e. , the surface where photosynthesis can not be performed , whether by direct feeding or drying out of the leaf due to the insect pest .
instead , we scored the average attack as follows : < 1% ( average 0.5% ) of leaf surface damaged ; 15% ( average 3% ) ; 520% ( average 12.5% ) ; 2050% ( average 30% ) ; 5090% ( average 70% ) ; and > 90% ( average 95% ) . to score the general level of infestation of a plantation
, we averaged all the average percentages of infestation of the 20 trees . at each plantation
, we also assessed the proximity with fallow lands , i.e. , we noted whether fields and hedges were directly adjacent to fallow lands or only to cultivated lands ( i.e. , where all assessed trees were at least 100  m from the next fallow ) . for fields , we also noted whether the field itself was left as fallow or weeded . when the field was not weeded , we considered it as a fallow . to further assess the influence of the distance to fallow lands on damage , in september 2012 we chose a field with 3-mo - old plants , weeded and intercropped with soybean , adjacent to fallow land at only one side , the three other sides being occupied by various weeded crops .
we assessed the level of infestation , using the same scale , of five randomly selected trees at 1 , 6 , 11 , 16 , 22 , 28 , 33 , 38 , 43 , and 48  m from the fallow land .
to compare the abundance of a. whitfieldi between the three cropping systems at the 12 sites where beetle populations were monitored during 1 yr , we used a linear mixed effects model with cropping system as fixed factor , village as random factor , and the sum of beetle number per field as dependent variable . to analyze the influence of cropping systems and environmental factors on the level of infestation by a. whitfieldi at the 31 plantations monitored in september 2012 ,
generalized linear models were used to fit a gamma regression to infestation scores . fixed factors used were j. curcas as hedge versus fields ( all data ) ; monoculture versus intercropping ( fields only ) ; and j. curcas plants adjacent to fallows in or outside the fields ( all data and fields only ) . in the 3-month - old j. curcas field adjacent to fallow lands
, the relationship between the level of infestation by the beetle and the distance to the nearest fallow was analyzed using a pearson correlation .
the yearly abundance of a. whitfieldi at the 12 plantations is shown in figs . 1 and 2 .
it appears before the main rains in april , but it becomes abundant only when the rainy season is well established , i.e. , in late june and july .
there was no significant difference in abundance between the different cropping systems ( f  =  11.451 , p  =  0.080 , df  =  2,6 ) . 

1.average number of a. whitfieldi adults per tree in the six fields in lo : two hedges , two intercropped fields , and two monocultures , between sept . 2012 and sept .
2.average number of a. whitfieldi adults per tree it the six fields in biha : two hedges , two fields intercropped fields , and two monocultures , between sept .
average number of a. whitfieldi adults per tree in the six fields in lo : two hedges , two intercropped fields , and two monocultures , between sept .
average number of a. whitfieldi adults per tree it the six fields in biha : two hedges , two fields intercropped fields , and two monocultures , between sept .
beetles were found at all 31 field sites surveyed in september 2012 , with mean percentages of leaf surface damage varying from 0.5 to 39.5% .
the type of cropping system did not significantly affect damage levels ( hedges vs. fields , p  =  0.463 , wald   =  0.538 ; intercropped field vs. monoculture , p  =  0.573 , wald   =  0.318 , df  =  1 ) ( fig .
3 ) . however , the presence or absence of fallow land within or besides the plantation was important , i.e. , a. whitfieldi was significantly more abundant on plants that were in the vicinity of fallows or when the field itself was not weeded ( p  =  0.001 , wald   =  11.97 with all data ; p  =  0.027 , wald   =  4.92 with fields only , df  =  1 ) ( fig .
3.percentage of leaf surface of j. curcas damaged by a. whitfieldi in 13 monoculture fields , 8 fields where j. curcas was intercropped with other plants , and 10 living hedges .
4.percentage of leaf surface of j. curcas damaged by a. whitfieldi in plantations in or adjacent to fallow lands compared with plantations where no fallow land occurred at < 100  m from the assessed trees .
percentage of leaf surface of j. curcas damaged by a. whitfieldi in 13 monoculture fields , 8 fields where j. curcas was intercropped with other plants , and 10 living hedges .
percentage of leaf surface of j. curcas damaged by a. whitfieldi in plantations in or adjacent to fallow lands compared with plantations where no fallow land occurred at < 100  m from the assessed trees .
the importance of the proximity of fallows was confirmed by the separate observation in a plantation of 3-month - old j. curcas plants beside a fallow land .
the level of attack by a. whitfieldi was significantly negatively correlated with the distance to the fallow ( r  =  0.590 ; p  <  0.001 )
. trees at 1  m of the fallow were defoliation at 85% , whereas those situated at more than 10  m of the fallow were defoliated at < 40% and those at 38  m or more were defoliated at < 10% ( fig . 5 ) . in the first 6 m from the fallow ,
5.percentage of leaf surface of j. curcas damaged by a. whitfieldi in a plantation intercropped with soybean , adjacent to a fallow , according to the distance from the fallow . 
 
percentage of leaf surface of j. curcas damaged by a. whitfieldi in a plantation intercropped with soybean , adjacent to a fallow , according to the distance from the fallow .
our long - term observations showed that population densities of a. whitfieldi and their damage on j. curcas were particularly high in the second half of the rainy season .
seem to be absent or less prevalent on j. curcas in dry areas ( terren et  al .
furthermore , j. curcas loses a large part of its leaves during the dry season , which does not favor the continuous presence of defoliating insects such as aphthona spp .
it was common to observe newly planted seedlings totally defoliated and even killed by a. whitfieldi ( a. s. unpublished observations ) .
this study failed to show a significant difference in damage level in the different cropping systems , i.e. , on hedges , monoculture plantations , or intercropping .
thus , the common observation that crops and trees are less vulnerable to pests in intercropping systems and mixed stands than in monocultures ( e.g. , andow et  al .
1991 , jactel and brockerhoff 2007 ) was not verified for a. whitfieldi on j. curcas .
nevertheless , in this preliminary study , we considered all intercropping systems together because we had no control on the associated crops , which varied not only between fields but also within the same field between seasons and years .
it can not be ruled out that a specific intercropping system could be found that would be able to lower pest populations , e.g. , by repelling beetle or by attracting or hosting natural enemies .
for example , in the region of kinshasa , drc , minengu et  al .
when j. curcas was intercropped with maize and the legume plant stylosanthes guianensis ( aublet ) .
furthermore , there is a general agreement that , in africa , hedges and wide intercropping j. curcas systems should be favored over monocultures for economic , risk management , and food security reasons ( e.g. , jongschaap et  al .
interestingly , a. whitfieldi seemed to be favored by the direct vicinity of fallow lands ( wild grasses ) , including when j. curcas is planted in nonweeded land .
since we did not find a. whitfieldi on wild plants despite extensive surveys around j. curcas fields ( a. s. unpublished observations ) , it is likely that the lower abundance of the pest in a clean environment is not due to the absence of wild hosts .
instead , it may rather be due to less favorable conditions for the immature stages ( eggs , larvae , and pupae ) in the soil .
indeed , weeding or ploughing the soil may affect immature stages , either directly or indirectly , by causing unfavorable abiotic conditions .
unfortunately , for the moment , little is known about the biology and ecology of a. whitfieldi , in particular during the immature stages . for example
, it is still unclear in which stage the insect spends the dry season and how it survives the drought , how many generations it may have during the rainy season , what are its alternative host plants , etc . as other members of the alticinae subfamily , eggs are most probably laid on the ground and the larvae feed on roots .
several european aphthona spp . used for the biological control of invasive euphorbiaceae in north america
but these are temperate species , univoltine with an obligatory diapause in the soil the larval stage , broken by winter cold .
it is likely that afro - tropical species have a very different bio - ecology that remains to be investigated before sustainable control can be developed .
aphthona spp . can be easily controlled by chemical insecticides but their use is neither economically nor environmentally sustainable in africa ( cassimo et  al .
2015c ) . based on preliminary observations described in this article and elsewhere , several recommendations can already be suggested for the control of a. whitfieldi and probably other aphthona spp .
in other regions in africa . these recommendations will have to be tested through proper field experiments before being implemented .
first , early plant establishment is critical , since the flea beetles are most damaging on young seedlings ( rouamba 2011 , minengu et  al .
2015a , c ) and , as shown by this study , mainly occurs in high numbers in the second half of the rainy season .
thus , every effort should be made to favor the fast growth of newly planted seedlings in the first part of the rainy season , by planting early and by planting as intercropping with fertilized crops , e.g. , maize .
second , although the reasons are still unclear , we also showed that a. whitfieldi is more abundant in badly maintained ( i.e. , not weeded ) fields and in the close vicinity of fallows
furthermore , attention should be paid to seedlings planted right beside older j. curcas plants , even if these do not appear much affected .
established plants always sustain a variable level of flea beetles in the lower part of their crown ( a. s. unpublished observations ) and will act as a source of beetles for young , vulnerable seedlings .
 the flea beetle aphthona whitfieldi bryant ( coleoptera : chrysomelidae ) is the main pest of the bioenergy crop jatropha curcas l. ( euphorbiaceae ) in burkina faso and several other west african countries . 
 adults severely defoliate plants , resulting in seedling mortality , poor growth , and low yields . to study the population dynamics of the pest in the sissili province of burkina faso , 
 12 sites were monitored weekly during a year and 31 sites were inspected for damage at the peak period of insect abundance . 
 the effect of cropping systems ( hedge , intercropping , and monoculture ) and surrounding vegetation on population densities of a. whitfieldi was assessed . 
 beetles were rarely found in the dry season and peaked in the second half of the rainy season . 
 the cropping system did not significantly influence the abundance and attack level . 
 in contrast , the close vicinity of fallow lands seems to increase damage levels . 
 many aspects of the biology and ecology of a. whitfieldi remain to be investigated before sustainable control methods can be developed . 
 however , this study already allows us to propose recommendations for further research on management . 