Selective chemical control techniques for the desert locust, Schistocerca gregaria (Orthoptera : Acrididae).

El-gadgoud, Khaled Mohamed (1999) Selective chemical control techniques for the desert locust, Schistocerca gregaria (Orthoptera : Acrididae). University of Southampton, Doctoral Thesis.

Abstract

The possibility of improving chemical spray applications has been explored with the aim of achieving more efficient locust control which is hazardous to non-target organisms.

Microencapsulated insecticide formulations with three wall capsule thicknesses (small, medium and large) were assessed in three trials against second instar desert locust hoppers. The results showed that poor suspension time and the aggregation of capsules affected the efficiency of the microencapsulated formulations, and it is suggested that further improvement to the physical properties of the formulation are needed.

The way in which the locust body collects insecticide, either directly in the form of spray droplets or indirectly from residues on the vegetation was also studied. Dead desert locust adults were mounted on artificial supports, stimulating the roosting sites. Three projected surface areas of the locust body were tested. The man droplet number detected on the total surface area of the locust was highly significantly different between the three surfaces. However, there were no significant differences in droplets collected on those surfaces when measured as the mean number per unit area.

There was a highly significant correlation between the number of droplets collected on the locusts bodies and the volume of spray used. Locusts were mounted on a support four different orientations. Using the correlation parameters derived experimentally, a mathematical model was developed to predict the insecticide dose that was received in each position.

It was shown that fifth instar hoppers can pick up about 50% of the insecticide deposited on a leaf surface as a result of a single contact. The amount taken up increases if there are further contacts with contaminated vegetation, but decreases if there are further contacts with clean vegetation. A spreadsheet model has been developed which predicts the insecticide dose collected by fifth instar hoppers on contact with barley plants, and the mortality caused by that dose.

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