repeated assessment of the abundance and diversity of phytophagous and entomophagous arthropods in crops is needed for ecological studies of population dynamics and species interactions , including the study of biological control .
rice is a major staple food , with a high potential for biocontrol by entomophagous arthropods , but which can be disrupted by insecticides .
the diversity of arthropods in rice crops can be high , and arthropod species occupy various crop strata ( e.g. , ground , stem , canopy , flowers ) , differ in mode of movement ( e.g. , walking , jumping , flying ) and foraging strategy ( e.g. , sessile sucking insects , hunting predators and flower visiting pollinators ) .
there is a wide range of arthropod sampling techniques , each with strengths and weaknesses .
for instance , pitfall traps can be used to sample ground - dwelling arthropods , but provide activity - dependent relative population estimates .
sweep nets can be used to sample fast - flying insects in the canopy , but give relative estimates of arthropod abundance .
the beat sheet method can be used to sample the plant - dwelling arthropod community and provides absolute estimates of arthropod abundance , but it can not be used effectively in flooded crop fields such as rice paddies .
suction sampling , when conducted in combination with an enclosure covering a standardized area of the field , provides absolute estimates of the densities of plant - dwelling arthropods .
the dietrick vacuum ( d - vac ) is the first commercially developed suction sampler .
although d - vacs are still widely used , they are relatively expensive , have a limited suction force and are relatively heavy , which makes them hard to handle in flooded rice fields . arida and heong   developed a suction sampler using a petrol - driven leaf blower - vac , and
advantages of the blower - vac suction sampler as compared to the d - vac are that it is much cheaper and easier to handle . although the blower - vac suction sampling method has been used in many ecological studies , the instructions for its modification and application have not been clearly described . here
we present a video - based , detailed description of the modification and application of a petrol - powered leaf blower - vac for suction sampling of arthropod populations in flooded rice fields .
the modification is inspired by arida and heong   and domingo and schoenly , but the design has been further simplified compared to these original publications , facilitating construction and use .
collect all parts listed in the materials list . connect all polyvinyl chloride ( pvc ) pipes with unplasticized polyvinyl chloride ( u - pvc ) glue ( pipes 1 - 2 - 3 - 4 - 5 and 6 - 7 ) .
drill three holes that are evenly distributed around the suction mouth of the machine . connect the machine to the end 1 of pvc pipe 1 - 5 by inserting one screw into each of the three holes . do not use glue to connect pipe end 1 to the machine because the connection should be reversible to clean the fan .
note : in case the diameter of the suction mouth of the machine differs from the model described here , the diameter of pipe end 1 should be adjusted to fit the machine seamlessly .
put the piece of metal gauze between the hose and the mouth part ( pvc pipes 6 and 7 ) to prevent the sampling net from being sucked into the machine .
connect the hose to pipe ends 5 and 6 with metal clamp hoops . remove the bottom from a plastic bucket ( 50 l , 40 cm bottom diameter ) .
this size of the enclosure covers 2 - 4 rice hills in a  transplanted rice field , depending on crop stage .
attach a nylon mesh sleeve , with a length of 1 m , to the top of the bucket using a rubber band .
for this sleeve , use a mesh size that is small enough to prevent the escape of the smallest target arthropods . use a diameter less than 0.5 mm . use two persons to operate the device in the field .
one person operates the blower - vac and the other handles the bucket enclosure and the sampling nets .
insert a sampling net into the mouth part of the blower - vac and fix it with a rubber band . for the net , use a mesh size that is small enough to catch the smallest target arthropods , but does not create obvious airflow resistance . use the light nylon material with a mesh diameter between 0.2 - 0.5 mm .
place the enclosure quickly over the plants at a random location in the field and push the bottom of the bucket firmly into the soil .
make sure that the sleeve is closed to prevent arthropods from escaping from the top of the enclosure .
remove all arthropods from inside the enclosure in a top - down spiraling way , for a standardized sampling duration . for rice crops in the vegetative and reproductive stages ,
use sampling durations of 1 and 2 min , respectively . after finishing the sample ,
remove the rubber band from the sampling net , quickly close the net and take it out of the mouth part of the blower - vac and close it with a knot , while keeping the machine running .
repeat steps 3.2 to 3.5 at random locations in the field for the next samples .
the number of replications depends on the variation in the spatial distribution of arthropods in the field , the required accuracy of the estimate and the purpose of the study .
typically , six replicates will give a good impression of the arthropod community and species abundances .
collect all parts listed in the materials list . connect all polyvinyl chloride ( pvc ) pipes with unplasticized polyvinyl chloride ( u - pvc ) glue ( pipes 1 - 2 - 3 - 4 - 5 and 6 - 7 ) .
drill three holes that are evenly distributed around the suction mouth of the machine . connect the machine to the end 1 of pvc pipe 1 - 5 by inserting one screw into each of the three holes . do not use glue to connect pipe end 1 to the machine because the connection should be reversible to clean the fan .
note : in case the diameter of the suction mouth of the machine differs from the model described here , the diameter of pipe end 1 should be adjusted to fit the machine seamlessly .
put the piece of metal gauze between the hose and the mouth part ( pvc pipes 6 and 7 ) to prevent the sampling net from being sucked into the machine .
remove the bottom from a plastic bucket ( 50 l , 40 cm bottom diameter ) .
this size of the enclosure covers 2 - 4 rice hills in a  transplanted rice field , depending on crop stage .
attach a nylon mesh sleeve , with a length of 1 m , to the top of the bucket using a rubber band .
for this sleeve , use a mesh size that is small enough to prevent the escape of the smallest target arthropods . use a diameter less than 0.5 mm .
one person operates the blower - vac and the other handles the bucket enclosure and the sampling nets . insert a sampling net into the mouth part of the blower - vac and fix it with a rubber band . for the net , use a mesh size that is small enough to catch the smallest target arthropods , but does not create obvious airflow resistance . use the light nylon material with a mesh diameter between 0.2 - 0.5 mm .
place the enclosure quickly over the plants at a random location in the field and push the bottom of the bucket firmly into the soil .
make sure that the sleeve is closed to prevent arthropods from escaping from the top of the enclosure .
remove all arthropods from inside the enclosure in a top - down spiraling way , for a standardized sampling duration . for rice crops in the vegetative and reproductive stages ,
use sampling durations of 1 and 2 min , respectively . after finishing the sample ,
remove the rubber band from the sampling net , quickly close the net and take it out of the mouth part of the blower - vac and close it with a knot , while keeping the machine running .
repeat steps 3.2 to 3.5 at random locations in the field for the next samples .
the number of replications depends on the variation in the spatial distribution of arthropods in the field , the required accuracy of the estimate and the purpose of the study .
typically , six replicates will give a good impression of the arthropod community and species abundances .
a total of 295 arthropods were collected in 8 three - minute blower - vac samples from a rice crop in the ripening stage in jiangxi province , china , in september 2015 . to determine the relationship between relative yield ( proportion of the arthropods collected in the sample ) and sampling duration ,
the mean number of individuals per sample was 36.9  4.1 ( mean  sem ) .
a total of eight arthropod orders were found , with hemiptera ( 28.8% ) , araneae ( 27.5% ) and diptera ( 17.6% ) being dominant ( figure 1 ) .
the relative yield , expressed as a percentage of the number of collected arthropods after three minutes , was 52.9%  5.1 , 92.4%  1.9 and 97.3%  0.9 after 30 seconds , 2 and 2.5 minutes , respectively ( figure 2 ) .
figure 1.species composition ( at the order level ) of arthropod samples in the suburbs of nanchang city in jiangxi province , china .
cumulative relative yield as a function of total sampling duration based on sub - samples of 30 seconds each .
the total number of arthropods collected over a sampling duration of three minutes is set at 100% .
suction sampling is one of many possible methods to sample arthropod communities in crops . for scientific research in rice systems ,
suction sampling is an appropriate option because the method provides absolute estimates of arthropod densities , it is non - destructive , and  in contrast to visual counts  allows collection and storage of samples for later processing .
compared to the commercially available d - vac , the blower - vac is smaller , lighter and easier to handle in ( flooded ) rice fields and also easier to combine with an enclosure . for example , a blower - vac weighs about 6 kg , whereas the backpack d - vac model , presented as the international standard for insect sampling , has a weight 12 kg .
more importantly , the sampling efficiency of the blower - vac is higher than the d - vac , while the cost of the blower - vac is less .
the modification of a leaf blower - vac into a suction sampler does not require special skills or equipment and takes less than an hour after all additional parts have been collected .
the blower - vac described here is easier to construct and operate than versions described previously in the literature , and the required parts ( table 1 ) are standard construction materials that are widely available .
this makes the blower - vac also accessible to researchers with small budgets in developing countries .
the power and displacement of the engine determines the suction force of the blower - vac .
here we recommend a machine with a power between 0.7 - 1.2 kw and a displacement between 25 - 35 cc , which is adequate for sampling the plant - dwelling arthropod community in rice .
the length of the flexible plastic hose and the diameter of the sucking mouth part ( pipe 7 ) are critical for a good sampling performance .
a hose that is too long will reduce the suction power , whereas a hose that is too short will be inconvenient to use during sampling . similarly , a mouth part with too large
a diameter will reduce the suction power , whereas a diameter that is too small will reduce the sampling efficiency due to the small surface .
if sampling is conducted throughout the growing season , the sampling duration may have to be adjusted to the plant size , structure , and planting density to maintain a similar level of efficiency .
sampling efficiency should be checked by careful visual inspection of the enclosed area after sampling .
the recommended sampling durations for rice crops in the vegetative stage is 1 minute  and in the reproductive and ripening stages it is 2 minutes .
suction sampling with the blower - vac can be conducted in flooded fields , while alternative methods , such as pitfall and beat sheet sampling are not feasible in standing water .
the blower - vac can also be used to sample the arthropod community on the water surface of flooded rice fields ( e.g. , predatory water bugs ) , as the machine is capable of sucking in some water .
however , it is not recommended for sampling aquatic arthropods as the motor may stop running when the mouth part is inserted deeply into the water and the airflow is blocked .
apart from rice , the blower - vac can also be used in other crops and non - crop habitat , as long as the height and structure of the vegetation allows proper placement of the enclosure .
almost all arthropods collected in the sampling net survived , including those soft bodies such as mosquitos and damselflies .
the blower - vac in the field will result in some disturbance , and therefore this method may underestimate disturbance - sensitive species such as grasshoppers . fast and
abrupt placement of the enclosure in a relatively undisturbed area in the forward direction of movement may limit this potential bias .
the loud noise of the blower - vac machine may also cause disturbance , and sampling at night in residential areas is not recommended .
the method is not suitable for sampling highly mobile flying insects , such as predatory odonata or larger hymenopterous parasitoids . as with any sampling method ,
the combination of the blower - vac with other methods , such as sweep net sampling or destructive harvesting of plants , can provide a more complete and balanced assessment of the arthropod community .
 rice fields host a large diversity of arthropods , but investigating their population dynamics and interactions is challenging . here 
 we describe the modification and application of a leaf blower - vac for suction sampling of arthropod populations in rice . when used in combination with an enclosure , application of this sampling device 
 provides absolute estimates of the populations of arthropods as numbers per standardized sampling area . 
 the sampling efficiency depends critically on the sampling duration . in a mature rice crop , a two - minute sampling in an enclosure of 0.13 m2 yields more than 90% of the arthropod population . 
 the device also allows sampling of arthropods dwelling on the water surface or the soil in rice paddies , but it is not suitable for sampling fast flying insects , such as predatory odonata or larger hymenopterous parasitoids . the modified blower - vac is simple to construct , and cheaper and easier to handle than traditional suction sampling devices , such as d - vac . 
 the low cost makes the modified blower - vac also accessible to researchers in developing countries . 
Introduction
Protocol
1. Modification of a Leaf Blower-vac for Suction Sampling
2. Prepare the Sampling Enclosure
3. Field Application of the Modified Leaf Blower-vac for Suction Sampling
Representative Results
Discussion
Disclosures