Alternative Strategies for Controlling the Brown Locust, Locustana pardalina (Walker)

Regular and often intense outbreaks of the brown locust, Locustana pardalina (Walker), in the semi-arid Nama Karoo region of South Africa present a formidable pest control problem. Outbreak patterns over a 64-year period (1941–2005) were reviewed indicating a very high frequency of outbreak years with regular ‘plague’ periods being experienced, while a more detailed analysis of the numbers of locust targets controlled during a 22-year period (1983–2005) described the intensity and scale of the outbreaks. The operational constraints associated with the traditional ground-based control strategy employed against the thousands of individual roosting brown locust hopper band and swarm targets in the Karoo are discussed. A brief review of laboratory and field trials of alternative methods of controlling the brown locust, such as insecticide baits, barrier treatments and the Green Muscle® myco-insecticide, as an alternative to broad-spectrum pyrethroid insecticides are described. In addition, alternative control strategies to the current ‘Commando’ system of ground-based control operations are discussed. The recommendation is for a modernised and technology-equipped integrated brown locust management strategy (IPM), combining ground and aerial tactics that will have the flexibility and the capacity to deal effectively with outbreaks. The integrated management strategy should focus on ground-based control of hopper bands and fledgling swarms in the Upper and eastern Karoo, while outbreaks over most of the Central Karoo and arid Bushmanland areas should be left to fledge and coalesce into large-sized swarms that could then be targeted by spray aircraft as they migrate along their known swarm flight paths. The introduction of electronic reporting and GIS mapping technologies for brown locust campaign management is essential.

Endocrine Activity During Insect Embryogenesis. Control of Events in Development Following the Embryonic Moult (Locusta Migratoria and Locustana Pardalina, Orthoptera)

1. Secretory activity of the ventral head glands in embryos of Locustana pardalina and Locusta migratoria is necessary for inducing the moult and controlling subsequent events in late development. 2. Continued secretory activity of the glands for a period after the moult is required for further progress in development. 3. The development hormone released by the glands activates in turn the pleuropodial glands. The latter, in order to become fully functional, also require the continued secretory activity of the endocrine glands for a period after the moult. 4. The enzyme-substrate system responsible for the formation of melanin does not become active until the development hormone is liberated. However, the system was present in the egg beforehand in an inactive state and it is suggested that it is held in check by an inhibiting influence. 5. The amount of melanin deposited appears to be correlated with the amount of development hormone released.

Endocrine Activity During Insect Embryo-Genesis. Function of the Ventral Head Glands in Locust Embryos (Locustana Pardalina and Locusta Migratoria, Orthoptera)

1. A brain-ventral head gland system operates in embryos of Locustana pardalina and Locusta migratoria. 2. The initiation of growth and differentiation on the termination of diapause in the egg of pardalina takes place before the ventral head glands are formed. 3. Maximal activity in the ventral head glands coincides with the retraction of the epidermis from the cuticle. 4. Embryos, dissected out of the egg, were kept alive in aerated sterile Ringer's solution for up to 2 weeks during which time they progressed in their development. 5. If post-katatrepsis embryos are ligatured between the thorax and abdomen before a ‘critical’ period the moult is limited to the thorax. If ligatured immediately behind the head, the body fails to moult. 6. Since on the termination of diapause in the egg of pardalina mitosis begins before the formation of the ventral head glands, it is suggested that in locust embryos these glands are exclusively concerned with the retraction of the epidermis from the cuticle. 7. It is suggested that the uptake of water by the egg of pardalina in stretching the cells stimulates a growth factor which, although present throughout the diapause phase, is only capable of initiating mitosis after the diapause phase has come to an end.