Radar and opto-electronic measurements of the effectiveness of Rothamsted Insect Survey suction traps

Abstract

Radar methods have been extended to measure the aerial density of small insects. Results obtained during an outbreak of the cereal aphid Metopolophium dirhodum (Walker) in south-eastern England were compared with simultaneous suction trap catches to study the sensitivity of trap effectiveness to windspeed. Two traps were studied: the Rothamsted Insect Survey trap (12-2-m) and a standard aerofoil trap. The Survey trap effectiveness is moderately sensitive to windspeed, decreasing exponentially by a factor of two for each 2-4 m/s (5 knots) of average windspeed. The two trap sensitivities did not differ significantly, but both results are very significantly different (P<0-001) from the published predictions, which were based upon a comparison of catches from suction traps and a combination of a rotary (whirligig) net and a tow net. These differences are discussed. The average catching rate is about 40% of that of an ideal trap. Seven-day catches could vary by a factor of 0-5-2-0 from average due to prolonged periods of extra strong or light winds. Systematic windspeed gradients can corrupt suction trap studies of insect dispersal in relation to vertical density profiles, diurnal flight patterns and geographical distribution. Absolute calibration of the aerofoil trap was achieved by using the remote-sensing IRADIT infra-red system to measure the aerial density of aphid-size insects near to the trap inlet in very light winds; the effectiveness was not statistically different from unity, and the Survey trap is expected to perform similarly. IntroductionThe Rothamsted Insect Survey (12-2-m) suction trap (Taylor & Palmer, 1972) has become a standard tool for monitoring the density of flying insects, particularly aphids. A network of traps, at present at 23 sites, has been managed by the Survey for 15 years in the United Kingdom, and in recent years similar traps have been operated throughout Europe (Taylor et ai, 1981). The Survey trap takes in air from a height of 12-2 m (40 ft) at the rate of approximately 0-8 m 3 /s, through a circular inlet pipe with a diameter of 0-254 m (10 in.) at a speed of about 16 m/s. Trapped insects are removed daily, the aphids identified and weekly bulletins distributed to the agricultural industry giving warnings of impending outbreaks (Woiwod et ai, 1984).The 'efficiency' of suction traps for quantifying the aerial density of passing insects has been assessed by Taylor (1962) by an indirect method. The insect catching rates of a variety of traps were measured relative to that of an aerofoil trap with an inlet diameter of

Relative importance off environmental variables in determining the growth off nestling Tree Swallows Tachycineta bicolor

“…The 12-m Rothamsted suction trap used in this study is designed to be immune to the effects of wind on trap efficiency (Muirhead-Thomson 1991). However, it is still possible that some of the negative relationship found between insect abundance and wind speed is partly due to the decreasing efficiency of the suction trap at high wind velocities (Schaefer et al 1985).…”

Sampling Adults with Non-attractant Traps

“…Errors are approximately within ±1%. Schaefer et al (1985) used radar methods and the remote sensoring IRADIT infra-red system to measure aerial densities of insects near the Rothamsted Insect Survey (lO-in diameter) traps positioned with their inlet at 12•2 m, and aero foil traps (l2-in diameter). The aim was to study the effectiveness of these suction traps in relation to increasing wind speeds, such as when traps are used at elevations or in exposed areas.…”

Sampling Adults with Non-attractant Traps

“…Errors are approximately within ±1%. Schaefer et al (1985) used radar methods and the remote sensoring IRADIT infra-red system to measure aerial densities of insects near the Rothamsted Insect Survey (lO-in diameter) traps positioned with their inlet at 12·2 m, and aerofoil traps (l2-in diameter). The aim was to study the effectiveness of these suction traps in relation to increasing wind speeds, such as when traps are used at elevations or in exposed areas.…”