Juvenile hormone (JH) was shown to effect the central nervous processing of aggregation pheromones in the antennal lobe (AL) of the desert locust, Schistocerca gregaria resulting in changes in the aggregation behaviour. The aggregation behaviour of gregarious male and female desert locusts was monitored for individual control insects or insects subjected to either of three treatments; allatectomy, sham-operation and JH-injection. Two parameters were recorded to characterise aggregation behaviour (a) tendency to aggregate and (b) changes in behavioural activity, in a two-choice bioassay applying the main adult aggregation pheromone component phenylacetonitrile (PAN) in the treatment arena. Individual locusts were monitored at days 1, 8, 15, 22 and 29 after adult emergence in order to evaluate behavioural changes over time. Both male and female control and sham-operated locusts displayed behavioural changes coinciding with the naturally fluctuating JH-titre. Locusts generally displayed an increase in aggregation tendency and in behavioural activity up to days 8 and 15, which coincided with a low titre of JH. At days 15, 22 and 29, coinciding with a high JH titre, locusts displayed an initial (days 15 and 22) increase in behavioural activity and a tendency to avoid the treatment area followed by a low behavioural activity and no apparent attraction or repellency (at day 29). Locusts that were deprived of (allatectomised) or injected with JH either displayed a high behavioural activity and a high tendency to aggregate or did not show any specific behavioural response respectively. Intracellular recordings from projection neurons (PNs) in the antennal lobe of 8 and 29 days old control, allatectomised and JH-injected locusts revealed differences in the central olfactory processing; low JH-level (young and allatectomised) locusts displayed a fully functional olfactory system whereas high JH-level locusts displayed impairments in the olfactory system. In order to exclude the possibility of a diminished sensory input to the AL, electroantennograms (EAG) were performed. No significant differences in EAG amplitude between the three groups were observed. We conclude that the observed changes in aggregation behaviour may be regulated through a direct or an indirect effect of JH on the central nervous processing. We postulate that the observed behavioural indifference to PAN in high JH-level locusts arise due to a significant changes in the central nervous processing of aggregation pheromone components.

Index terms: Schistocerca gregaria, aggregation pheromone, electrophysiology

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