Density Distributions of Hoppers of the Red Locust, Nomadacris septemfasciata (Serv.) (Orth., Acrid.), in Relation to Control by Insecticides

1958 ◽  
Vol 49 (3) ◽  
pp. 467-478 ◽  
Author(s):  
C. C. Scheepers ◽  
B. J. Eyssell ◽  
D. L. Gunn
Keyword(s):  
Population Distribution ◽  
Egg Laying ◽  
Control Measures ◽  
Nomadacris Septemfasciata ◽  
Red Locust ◽  
Density Distributions ◽  
Outbreak Area ◽  
Observation Area ◽  
The Mean ◽  
Insecticide Control

In continuation of a study of the process of swarm formation in the Red Locust, Nomadacris septemfasciata (Serv.), to enable rational plans for control measures to be made, the population distribution of about 44½ million hoppers of the Red Locust was investigated in an observation area of 1,052 acres in the Iku outbreak area of the Rukwa Valley, Tanganyika Territory, from 18th January to 24th February 1957. to see if the hoppers showed a tendency to concentrate, which would have the effect of producing, immediately after the last moult, adult swarms from hoppers that were originally more scattered. From 25th January onwards, the estimated population remained constant in numbers. Densities over 50 per sq. yd. were unusual and, taking any continuous infestation over one per sq. yd. as a band, the mean density of hoppers in bands was 15 per sq. yd. There was a tendency for such bands to become larger by fusion and for the area quite free from locusts to increase slightly but the number of dispersed locusts increased. There would therefore have been no advantage in withholding insecticide control in the hope of attacking denser and more economical targets. Nevertheless, such populations have to be controlled.In the Red Locust, under the conditions described, it seems probable that the behaviour of the young adults is most important in the formation of dense swarms, while in certain other species but not in the Red Locust, concentrated egg-laying and the behaviour of the hoppers are also important.Investigations are required on more economical enumeration of patchy gregarious distributions.

The Effect of Climate and Weather on the Numbers of the Red Locust, Nomadacris septemfasciata (Serv.), in the Rukwa Valley Outbreak Area

1959 ◽  
Vol 50 (3) ◽  
pp. 507-521 ◽  
Author(s):  
P. Symmons
Keyword(s):  
Adult Population ◽  
Dry Season ◽  
Egg Laying ◽  
Control Measures ◽  
Multiple Regression Equation ◽  
Nomadacris Septemfasciata ◽  
Red Locust ◽  
Outbreak Area ◽  
Adult Locust ◽  
Very High

An examination of the records from 1930 onwards shows that a very high level of Lake Rukwa is correlated with small numbers of the red locust, Nomadacris septemfasciata (Serv.), in the Rukwa Valley outbreak area in Tanganyika. When the lake level is not very high, the size of the adult locust population (taken as that present in the middle of the dry season) is correlated negatively with the total rainfall of the last but one wet season (broadly, November–May), positively with the size of the preceding parental population (taken as that present at the time of oviposition) and possibly also with the rainfall of the preceding October–December, but not significantly with the date of the drop in temperature that is thought to be associated with the start of ovarian development.Three tentative explanations of the correlation between adult population and rainfall are offered. First, if the water-table is high because of heavy rain in the previous season, the early rains may make the soil unsuitable for successful egg-laying and incubation; second, after a season of heavy rainfall the grass cover may be particularly dense at the end of the following dry season and the consequent reduction of the oviposition sites may make breeding unsuccessful; third, parental mortality may be high during a dry season following heavy rains. These possibilities are being further investigated.It is suggested that by using a multiple regression equation incorporating the correlations that have been established, the size of the adult locust population can be forecast in time for the scale of hopper control measures to be appropriately modified and economies thereby achieved.

Enumerating Populations of Adults of the Red Locust, Nomadacris septemfasciata (Serville), in its Outbreak Areas in East and Central Africa

1958 ◽  
Vol 49 (2) ◽  
pp. 273-285 ◽  
Author(s):  
C. C. Scheepers ◽  
D. L. Gunn
Keyword(s):  
Total Population ◽  
Central Africa ◽  
Nomadacris Septemfasciata ◽  
Natural Mortality ◽  
Red Locust ◽  
Frequency Distributions ◽  
Moving Vehicle ◽  
The North ◽  
Outbreak Area ◽  
Outbreak Areas

SummaryA method is described of estimating the total numbers and frequency distributions of adults of the Red Locust, Nomadacris septemfasciata (Serv.), in outbreak areas of hundreds of square miles, based upon counting the numbers that fly up in a two-yard strip in front of a moving vehicle. The method has proved itself valuable for indicating both immediate and future requirements for killing the locusts, but it requires refining for some research purposes.By this method, the importance has been clearly shown of the process of congregation of scattered adult locusts in forming emigrant swarms that could start a plague. The locusts do not congregate but actually disperse just before laying eggs.The total population in part (189 sq. miles) of the North Rukwa Outbreak Area (a self-contained area of 253 sq. miles) in Tanganyika Territory has been followed for four years. There are indications that a small migrant swarm contains 5–10 million locusts, that a total population in the whole of the North Rukwa Outbreak Area of 20 million locusts is unlikely to yield a migrant swarm, but that 50 million locusts could readily do so.In 1953, after poor rains, no natural mortality was detected between July and October by the assessment methods described. In 1957, after good rains, natural mortality of 70–90 per cent. was revealed by the same methods, although the dry season was not fully covered by the assessments.

Some Factors affecting Breeding and Oviposition of the Red Locust, Nomadacris septemfasciata (Serv.)

1959 ◽  
Vol 50 (2) ◽  
pp. 333-353 ◽  
Author(s):  
P. Symmons ◽  
A. J. M. Carnegie
Keyword(s):  
Soil Moisture ◽  
Soil Temperature ◽  
Dry Season ◽  
Oviposition Site ◽  
Nomadacris Septemfasciata ◽  
Wet Season ◽  
Red Locust ◽  
Factors Affecting ◽  
Outbreak Area ◽  
Primary Object

Observations were made on the red locust, Nomadacris septemfasciata (Serv.), between October 1957 and February 1958 in an area of grassland, six miles long by one mile wide, marked out by beacons and divided lengthwise by a line of beacons down the centre, in the Rukwa Valley of south-west Tanganyika.One half of the plot had been burnt off completely in the latter part of the dry season; the other half was unburnt and carried in part a four-year accumulation of growth and in part an area of standing grass that had regenerated after a damaging fire during the previous wet season and then, for the most part, flooded. Vegetation profiles were made along the whole length of the plot, and rain gauges, soil thermometers and soil tensiometers were installed at regular intervals along the three lines of beacons. Assessments of the population and distribution of adult locusts within the plot were made from Land-Rover or on foot in mid-October, mid-December (ten days after the onset of the rains) and early in January. A systematic search was made for egg-pods, starting at the end of December, along furrows ploughed down the middle of each of a number of narrow strips mown in the grass in sets near each beacon and sampling equally the burnt and unburnt halves of the plot. The first hoppers were seen on 3rd January, and assessments of hopper populations were carried out four times during January.The primary object of the work was to study the effect on choice of oviposition site and on incubation success of the type and condition of the grassland (whether burnt during the previous dry season, at an earlier date, or left unburnt) and its possible bearing on control of the species in an outbreak area. Data were also obtained on the conditions of air temperature, soil moisture, soil temperature and rainfall in which eggs are laid and incubated; and the effect of variations in these factors on oviposition and on incubation success was examined.It was observed that, in the hot, dry conditions of mid-October, adult locusts were completely absent, from the recently burnt-over ground, and were found almost exclusively in that part of the standing grass that had suffered a wet-season burn. By mid-December, the locusts had spread out from the unburnt into the burnt-over zone, where the grass had put out fresh growth, but many were still to be found hi the former, with a concentration along the line of contact with the latter. By early January, the size of the population had been greatly reduced and it was evenly distributed over the whole plot.The distribution of egg-pods snowed that the locusts had laid almost exclusively in the burnt-over zone, about 50 per cent. being found within 0·1 mile of the line of contact with the unburnt zone.The hoppers were likewise almost exclusively confined to the burnt-over zone, and with numbers significantly higher in the ¼-mile band next to the contact line than in the band at ¼–½ mile from it. The numbers of hoppers in the unburnt grass was significantly lower than might have been expected from the results of the egg-pod survey, suggesting that survival was lower there than under fresh grass following a dry-season fire. A subsidiary experiment, in which adult locusts were confined in cages placed on the lately burnt-over zone, the early-burnt and unburnt areas, respectively, suggested that, where there was no choice of oviposition site, the greatest number of surviving egg-pods occurred in the first zone, almost as many in the second and about half as many in the third.During the incubation period, the soil under the unburnt grass was significantly colder, and tended to be moister, to moisten more slowly and to dry out less rapidly than that which had been burnt over. No significant correlation was found between incubation success in the burnt-over zone and total rainfall, mean recorded soil temperature or soil moisture.It is concluded that, since these observations show that, for oviposition, adults of N. fasciata exhibit a very significant preference for ground that has been burnt over in the previous dry season, the burning of selected strips should lead to the concentration of oviposition and, consequently, of hoppers, thus making chemical control of the latter easier and cheaper.There was some evidence, also, that when locusts could not move to bare ground, either oviposition or egg-pod survival (or both) were least successful where the grass cover was thickest.

Field trials with a presistent stomach insecticide against populations of the red locust, Nomadacris Septemfasciata (Serv.), in an outbreak area

1963 ◽  
Vol 54 (2) ◽  
pp. 349-359 ◽  
Author(s):  
G. J. W. Dean
Keyword(s):  
Standard Method ◽  
Field Trials ◽  
Nomadacris Septemfasciata ◽  
Mosaic Pattern ◽  
Tall Grass ◽  
Red Locust ◽  
Total Cost ◽  
Outbreak Area ◽  
Outbreak Areas ◽  
The Cost

In its potential outbreak areas in Northern Ehodesia and Tanganyika, sexually immature populations of adults of Nomadacris septemfasciata (Serv.) tend to concentrate in the islands of grass that remain unburnt after the annual fires that occur during the dry season. The locusts use the tall grasses as roosting sites and descend in the daytime to feed on adjacent short grasses, where these occur as constituents of an internal mosaic within the islands, or, in the case of islands composed wholly of tall grasses, on the fresh grass-shoots on the burnt-over ground surrounding them.Two methods are described whereby emulsified solutions of dieldrin were applied in the Central Bukwa plain, Tanganyika, in 1960 as a stomach poison at dosages of 2·9 and 4·5 oz. active ingredient per acre from aircraft to the whole of individual islands showing the internal mosaic pattern (4 trials) or at 2·9, 4·5 and 8·2 oz. per acre to a swath 20 or 40 yd. wide around the perimeter of tall-grass islands (8 and 4 trials, respectively). Results were assessed by counting the numbers of locusts flushed by a vehicle driven along strips parallel to one another and 0·1 mile apart, and checked by counts of dead locusts. Mortality reached at least 90 per cent, within four days, at either dosage, following the first method, and 21–89 per cent, within 14 days following the second, being significantly greater at the higher dosages but not with the wider swath.These results are compared with those obtained in preceding years by the standard method of applying DNC from aircraft at 20 per cent, in oil as a contact insecticide; in the latter case, the cost of insecticide was more per acre sprayed, but less per 1,000 locusts killed because the density (5 locusts per sq. yd. of grass island) in the trials was greater than in those using dieldrin (1 per 3 sq. yd.). Even so, when dieldrin was used, many more locusts were killed per sortie flown, and the total cost (of flying plus insecticide) per island was much less, and per 1,000 locusts killed very much less, than in the standard method, which nevertheless has to be used against mobile swarms because DNC is quick acting.

Assessing the size of populations of adults of the red locust, Nomadacris septemfasciata (Serv.), in their outbreak areas by means of a helicopter

1966 ◽  
Vol 56 (4) ◽  
pp. 715-723 ◽  
Author(s):  
P. M. Symmons
Keyword(s):  
Central Africa ◽  
Early Morning ◽  
Rotor Blades ◽  
Nomadacris Septemfasciata ◽  
Red Locust ◽  
Outbreak Area ◽  
South Central ◽  
Outbreak Areas ◽  
Considerable Length ◽  
On Line

Populations of the red locust, Nomadacris septemfasciata (Serv.), can build up to large numbers in certain of the grass plains of south-central Africa. Adult populations are always under-dispersed, and estimates of their size can be made economically only by counting the locusts flushed on line traverses of considerable length. It is necessary, in such traverses, to determine the width of the strip swept, the proportion of the locusts in it that are flushed, and the accuracy with which these are counted. Investigations into the use of a three-seat Hiller helicopter for this purpose were carried out in south-west Tanzania in 1964–65. It proved possible to cause virtually all the locusts in a strip the width of the rotor blades to rise ahead of the machine, provided it was flown at a height of about 10 ft. and at less than 10 m.p.h. and neither in the early morning nor in the late evening. A comparison of estimates of the size of the population in a 1-sq.-mile plot made by Land-Rover traverses with those made by helicopter, both when the traverse strip was marked on the ground and when it was assessed from within the helicopter, showed no evidence of systematic errors in estimating from the helicopter either the number of locusts flushed or the width of strip. Further, two observers simultaneously counting locusts rising from one strip achieved very similar results. Thus, estimation of the size of a complete outbreak-area population by means of a helicopter is clearly possible.

The assessment of the size of populations of adults of the red locust, Nomadacris septemfasciata (Serville), in an Outbreak Area

1963 ◽  
Vol 54 (3) ◽  
pp. 549-569 ◽  
Author(s):  
P. M. Symmons ◽  
G. J. W. Dean ◽  
C. W. Stortenbeker
Keyword(s):  
Standard Error ◽  
Large Scale ◽  
Considerable Proportion ◽  
Nomadacris Septemfasciata ◽  
Random Errors ◽  
Red Locust ◽  
Moving Vehicle ◽  
Outbreak Area ◽  
Outbreak Areas ◽  
Valid Estimate

Estimates of the size of populations of the red locust, Nomadacris septemfasciata (Serv.), in their outbreak areas have been made in Tanganyika from counts of adults caused to fly up by the approach of a slowly moving vehicle. For research purposes it was desirable both to improve and estimate the accuracy of such assessments. For control purposes it was desirable to devise an objective aerial assessment technique which could be used in areas where ground methods were either impracticable or expensive. The errors involved in both ground and air estimates can be divided into those concerned with the ratio of locusts counted in the sample area to those actually present, and those concerned with the distribution of the locusts.It was found that a Land-Rover moving at five miles an hour, with the wind blowing from a rear quarter, flushed a high and virtually constant proportion of locusts during most of the day and in the most important grasses of the Rukwa outbreak area, throughout the dry season. Variation in locust density and in the state of the grass had little effect, if any, on the value of the equivalent strip (e), i.e., a strip whose width is such that the number of locusts in it is equal to the number flushed by the vehicle in a strip equal in width to its own. The change with time, and thus presumably with locust behaviour, in the value of e, estimated as recommended, was small but significant.Counts by various observers in one vehicle gave similar results and it seems likely that, even with high numbers, there was no systematic mis-estimation. This is almost certainly true for counts of under a hundred locusts flushed per 0·1 mile. With upwards of one thousand 0·1-mile counts in each assessment, it is believed that the random errors due to mis-counting of the locusts flushed will be negligible.The locusts are always distributed in an over-dispersed manner, consequently normal techniques for ascertaining the standard error of estimate cannot be used. Three assessments were made by the methods recommended, using a grid of two-mile squares; in one case, where the distribution was very gregarious, the most densely populated sector was more intensively sampled. The standard error of assessments laid out in this way was estimated. The method of analysis overestimates the standard error to some degree. Alternatively, the standard error resulting from the nature of the locust distribution can be computed for assessments where the 0·1-mile counts can be shown to be distributed log-normally.Provided the population assessment is carried out under the conditions stipulated above, the additional errors will be minor. The effect of such errors will be likely to be so small that the estimated standard error, derived from the lognormal or assessment-grid analysis, may be regarded as a valid estimate of the standard error of the population estimate.An attempt was made to estimate populations of the red locust in part of an outbreak area from locusts flushed by a ‘ Prospector ’ aircraft. The trials suggested that, given a clear rear view, red locusts which were flushed could be identified as such. Further, the number of locusts flushed could be counted at low densities, and it is thought likely that a reasonably objective technique could be developed for estimation at higher densities.Flushing appeared to be most effective at an aircraft height of 20 ft. or less and when the direction of flight was with the wind. However, the majority of locusts present failed to take off and the proportion which did rise varied very greatly. The spraying of concentrated ammonia under pressure increased the efficiency of flushing.A large-scale comparison of air and ground assessments suggested that, under the prevailing conditions, a considerable proportion of the locusts could be flushed only from the dense concentrations. At all densities the proportion of locusts which the aircraft caused to rise was a small fraction of those present. With flushing of such a low level of efficiency, little idea could be obtained of the size of the locust population at a moderate or low density.

Dieldrin lattices applied by aircraft for controlling hoppers of the red locust, Nomadacris septemfasciata (Serville).

1960 ◽  
Vol 51 (3) ◽  
pp. 441-460 ◽  
Author(s):  
W.N. Yule
Keyword(s):  
Large Scale ◽  
Accurate Method ◽  
Nomadacris Septemfasciata ◽  
Lattice Distribution ◽  
Red Locust ◽  
Aqueous Emulsion ◽  
The North ◽  
Outbreak Area ◽  
Aircraft Pilots

Large-scale operational trials of dieldrin lattices applied by aircraft for controlling hoppers of the red locust, Nomadacris septemfasciata (Serv.), were carried out in the North Eukwa outbreak area in south-western Tanganyika during 1958 and 1959. Single swaths of dieldrin aqueous emulsion spray were applied by aircraft to vegetation at wide intervals and in two directions at 90°, forming a rectilinear lattice distribution of poisoned strips of vegetation over large, hopper-infested areas. Hoppers, especially those in bands, were killed on eating the poisoned vegetation in the strips which they encountered during their migrations. An accurate method of lattice layout by aircraft pilots without assistance from ground marking parties was developed, and the whole operation was used on a large scale for controlling the hopper infestation in North Eukwa in 1959.

Sign in / Sign up

Export Citation Format

Share Document