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The reporter used the time up to the commencement of the IRLCO-CSA assignment to evaluate the locust situation. Together with the representative of IRLCO-CSA in Malawi he visited the districts of Lake Chilwa and the Elephant Marsh in the Lower Shire Valley. The situation was as follows:
Lake Chilwa: At the northern edge of the lake basin dispersed populations of red locust were found in only one of five places visited. Dense populations are reportedly present further inland in marshy or flooded parts of the basin. In one village gregarious adults (7 eye strips) were being sold as food. The existence of swarming populations in the largely flooded areas lying further inland was therefore to be presumed. This was to be checked by prospection with the helicopter. There was hardly any damage due to locusts this year. So far the locusts have remained in the particularly lush natural vegetation.
Elephant Marshes: It was not possible to show the reporter any place with notable locust populations, there were only widely distributed insignificant frequencies (e.g. 200 insects) in the transient phase (8 eye strips). There was nothing to report from the well monitored private sugar cane plantation SUCOMA either.

In this situation it appeared advisable to prospect the region of Lake Chilwa and to treat it if this proved necessary. For safety reasons the Elephant Marshes were to be prospected by helicopter.

The IRLCO-CSA assignment to survey and control the locusts began on 21. May in the Lower Shire Valley.

During the first week of the reporter's assignment the funds approved for monitoring and prospecting were transferred from the GTZ project office to an account of the Ministry of Agriculture and Livestock Development. They served to finance
per diem allowances and overnight accommodation allowances
fuel, engine oil
during the monitoring and control measures.

The transfer of K 357,950 (approx. DM 42,100) was effected on the basis of a plan of expenditures submitted to the project service office by the Ministry (Annex 9.1). Only the amount for the inputs listed under Point A in Annex 9.1 was transferred. The funds for protective clothing were not awarded since no ground control measures were carried out.

The accounts will be settled by the GTZ project office on submission of invoices by the Ministry. The local Plant Protection Project will support the handling.

The insecticides were provided by the Ministry of Agriculture and Livestock Development. The costs of the helicopter and aircraft as well as per diem allowances and overnight accommodation allowances for the IRLCO-CSA staff were assumed by that organisation. During the first application for emergency aid, financing of the prospection and treatment costs had been requested and approved. However, IRLCO-CSA generally pays these costs from contributions from member countries. The application was therefore amended by the Malawian side to request that the funds thus released be allocated to the insecticides. However, in the opinion of the reporter and the Supra-regional Locust Project, the locust situation did not justify any further purchase of insecticides. At the start of the measure the ministry had stocks of about 10,000 Sumithion 100. Approximately 1600 litres were used in the course of this measure.

With the agreement of the reporter the ministry used a sum of approx. 1140 US$ from the funds provided for the purchase of 1600 1 fuel for the helicopter and 200 1 fuel for the treatment aircraft. These costs are actually assumed by the IRLCO-CSA. However, as a result of the strategy applied (intensive helicopter monitoring and direction of the aircraft on application by the helicopter) the fuel consumption exceeded the planned quantities.

• 1 helicopter of type Bell Jet Ranger 111, 4 seats
• 1 aircraft, type CESSNA 185 AGWAGON, equipped with 2 Micronair AU4000, 200 1 insecticide tank with electric pump
• 2 pick-up four-wheel drive vehicles for carrying staff (one additional four-wheel drive vehicle for part of the time)
• 1 truck for transporting fuel and insecticide
• 1 GPS
The insecticide used was:
• Sumithion 100 (approx. 10 years old).

The equipment used was in good condition. Any defects which occurred such as a leak in the feed-line to the Micronair AU4000 were eliminated promptly by mechanics.

Ministry of Agriculture and Livestock Development of Malawi:
• Assistant Director of the Department of Agricultural Extension and Training (DAET) for part of the time
• Head of the Department of Entomology from Bvumbve
• Representatives of the local administrations (ADD, Field assistance)
• 3 drivers, occasionally 4
• Staff for filling up and cleaning the aircraft and helicopter IRLCO-CSA:
• Scientist
• Representative of the IRLCO-CSA in Malawi
• 2 pilots
• 2 mechanics

Following the survey trip to the potentially infested areas described in Chapter 4.1, the IRLCO-CSA-Team arrived on 18.05.97.

The monitoring and prospections began in the Lower Shire Valley. The landing strip of the SUCOMA sugar cane plantation served as an airfield. The surveys were conducted with the helicopter which flew over the potentially infested areas at an elevation of 1-2 m. The locusts were found mainly in the 1-2 m high grass and flew up when the helicopter flew over them. By circling round the location the size of an infested area was estimated, its coordinates were noted by means of GPS and it was subsequently treated. The pilot carried an escort equipped with GPS with him, who guided him to the place to be treated.

However, the locust situation in the Lower Shire Valley was found to be altogether insignificant. At a meeting held in the ADD the suspicion was voiced that the flooding in January and February, the heaviest for at least 70 years, may have contributed to reducing the locust population. After one assignment day the team transferred to the Chilwa basin area. The military airport in Zomba was used as a base.

A first prospection flight by helicopter showed that the areas with crops in the west and north-west of the basin were almost free of locusts. However, in the north of the basin concentrations and small swarms of the red locust were identified. These were in the gregarious phase. However, the locust populations could not be recognised from the aircraft and a precise application of treatment agents over these areas proved to be difficult. Due to the patchy distribution of the locust population, large-scale treatment did not enter into question. For this reason it was decided to use the helicopter to guide the aircraft during treatment.

The following procedure was adopted for the treatment operations:

The helicopter positions itself over the leeward side of the area of locust concentration.

The aircraft passes over the first strip or track to be treated and flies past in front of the helicopter, which hovers at a sufficient altitude above the flying level of the aircraft. The aircraft must be careful not to fly too close beneath the helicopter, since otherwise it would come into conflict with the downwash current created by the helicopter. The Head of Operation in the helicopter gives the aircraft pilot instructions to switch the spray equipment on and off. He sees the locusts flying up beneath the aircraft and is in the best position to specify the length of the spray treatment tracks. The height of application was 3-5 m. In the course of treatment the helicopter moves upwind at intervals corresponding to the width of the treatment tracks (standard value 50 m).

This procedure made it possible to control the locust populations selectively. Two attempts at treatment without the assistance of the helicopter produced questionable results. The places for treatment had been marked in advance by rolls of toilet paper thrown out of the helicopter which unwound as they fell. The identification of the plot from the aircraft proved to be very problematic. This was aggravated further by the fact that it is very hard to see the locusts and that the concentration could have changed position in the meantime.

Nor was it possible to treat places whose coordinates are known properly using just the aircraft and a manual GPS instrument. The progress of treatment is too fast for the user of the GPS unit to be able to read off the data and give the pilot the correct flight instructions for the tracks to be treated. This is only possible with an appropriate GPS navigation system.

Despite the support for the aircraft provided by the helicopter, exact spraying with parallel tracks at regular 50 m intervals was not possible. These specifications are simply target values which are achieved to a greater or lesser extent depending on the circumstances. The direction of flight continually changed slightly, the intervals were too large or too small, tracks were flown over more than once, intersected, and after a track too far up was followed, a further track was flown between this and the previous track. Now and again the pilot had difficulties in flying a treatment path against the sun. For the helicopter it is difficult to maintain regular 50 m intervals since the vegetation surface is so monotonous. GPS provides assistance here. Three seconds represent approximately 50 m. It is true that the precision of the system lies specifically in this sector. However, if the individual GPS readings are not taken precisely but instead as a guiding value when relatively large numbers of treatment strips are flown, average treatment widths of 50 m are achieved.

Table 4 Treatments with Fenitrothion 100 against the red locust during the emergency aid measure in Malawi 1997

The often combined survey and treatment flights were generally flown once in the morning and once in the afternoon. The helicopter started first and reached the infested area after about 20 minutes. It then began to locate the places to be treated and to assess their extent. After about 10 minutes the aircraft followed and began to circle close to the helicopter. On instructions from the helicopter the treatment then commenced. Once the identified areas were treated and if the aircraft still had insecticide in its tank, the aircraft continued to circle while the helicopter sought out a new infested place. However, it also happened that treatment had to be interrupted due to the fact the insecticide tank was empty, or surplus insecticide had to be simply sprayed (insecticide may not remain in the aircraft tank after treatment). Renewed treatment of a swarm following interruption due to lack of insecticide was carried out at the earliest two days later. In this way a second treatment of locusts which had already received sufficient doses was to be avoided. After completion of the treatment the helicopter sought out the application locations for the next assignment before returning to the airfield.

The areas treated in the vicinity of Lake Chilwa are entered in the map in Figure 1. The plots marked show the approximate position of the places where insecticide was applied. The map illustrates the selective treatment of the infested areas. Non-infested areas in the infested district were left untreated.

In some cases multiple treatment of the same areas occurred. This may be due to the fact that after treatment further locusts flew in, that treatment had to be interrupted after the insecticide tank was emptied, or that the treatment was not effective enough. The observations set out in the next chapter concerning mortality favour the first two possibilities. The fact that only two assignments were flown per day was due partly to the low temperatures and partly to the number of daylight hours available each day. In the morning it was not possible to start before 09.00 h; the morning assignment was completed between 11.30 h and 12.00 h. After the lunch break work commenced again at about 14.00 h. The aircraft and helicopter had to be back at the airfield by 16.30 h at the latest, since it became dark at 17.30 h. On two days no flights were flown due to the cold weather.

With an insecticide tank capacity of 200 1 and two flights per day, the maximum possible treatment area was 800 ha. If no sufficiently large infested areas were found during prospections, however, the tank was not filled completely.

It was not possible to examine mortality by density determinations before and after treatment because - apart from a few exceptions - the treatments were carried out over flooded or marshy terrain and the vegetation consisted of dense grass 1 - 1.5 m high.

In order to obtain an indication of the effectiveness of treatment despite this, locusts were caught after treatment in two cases of treatment on dry land. It was not possible to pursue locusts flying up out of the treated area in the high grass. However, this did not turn out to be necessary since at the low temperatures of below 23° C the locusts were not very flight-active so that such swarming up was rare.

In a first case 29 locusts were caught with a sweeping net 10 to 30 minutes after treatment. Since it was not very warm and the catcher was running against a not too weak wind, catching was very simple. The catcher did not aim for the locusts which flew up last, but for those which flew up at a medium distance from him. It can be assumed that these locusts caught shortly after the application form a representative sample as regards the dose of insecticide received by the insects in the respective plot.

In a second case 21 locusts belonging to a swarm which had been treated in the morning were caught in the afternoon, about 5 - 6 hours after the application. In this case, however, it was mainly slower-flying locusts which found their way into the net. The random sample originated from that part of the population which already showed signs of treatment impact.

In both cases all locusts were dead one day after treatment. It cannot be concluded from this that the treatment mortality was 100%. However, in the case of selective treatment of locusts a high mortality rate which may range between 80% and 100% can be assumed.

The presence of a gregarious population of red locusts in the Lake Chilwa region justified the assignment of IRLCO-CSA in Malawi. The equipment, personnel input and strategy were ideally adapted to the situation. Non-treatment of the population could have led to a critical situation in the following hatching season.

The results of the emergency aid measure, selective control of locust concentrations with a high mortality rate in the vicinity of a region with one of the highest population densities south of the Sahara and with maize and rice crops urgently required to supply this population, justify the assignment.

An assessment of the economic efficiency of the measure is difficult. It is necessary to distinguish between the overall assignment and the contribution made by the GTZ. The latter largely concerned the per diem allowances and transport expenditures incurred during the assignment. The operating costs for the helicopter and aircraft were assumed by the IRLCO-CSA. The combined use of helicopter and aircraft is very expensive for control measures. By way of experience it can be assumed that the damage - which may have been - sustained the next year due to locusts would have been below the costs of the assignment.

However, in the case of locust control the preventive aspect must also be taken into account. This requires, for example, that gregarious populations must be controlled in order to prevent swarming. Economic assessments are not possible for individual cases in this connection.

The fact that a locust control organisation such as the IRLCO-CSA maintains its own helicopter is due above all to the fact that the red locust multiplies in marshy regions which are poorly accessible, if at all. If infested areas cannot be reached by land, effective control is only possible by helicopter. This is true above all for prospecting. The actual control could be carried out with aircraft if these were equipped with suitable navigation systems. If the helicopter is only used for prospecting and the aircraft could subsequently treat the areas defined precisely with the aid of a navigation system, the economic viability of control measures would be improved substantially.

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