Six electrophysiologically active aromatic compounds, viz., anisole, benzaldehyde, veratrole, guaiacol, phenylacetonitrile, and phenol, were identified in the volatiles of older-adult male desert locust. Young adults and females of all age groups produced none or only trace quantities of these compounds. Comparison of the aggregation responses of young and older adults to the crude, older-adult, volatile extract and different synthetic blends of the six compounds showed that the aggregation pheromone system of the adult gregarious locust consists of phenylacetonitrile, guaiacol, phenol, and benzaldehyde. Like the crude volatile extract of older males, neither the synthetic blend of the six compounds nor the adult pheromone blend evoked any significant aggregation responses from nymphs. These results confirm our previous report of sexual differentiation in the production of adult aggregation pheromone in the desert locust and of the evidence of two distinct aggregation pheromone systems in the two stages of the insect.

Termites encounter a diverse array of potentially useful and harmful fungi in their subterranean habitats. These vary from symbiotic to harmful species with varying levels of virulence. How these hemiedaphic insects survive in habitats with infective fungi is not well understood. Possible mediation of olfactory signals in avoiding contact with entomopathogenic fungi has been explored by a number of workers. In the present study, we initially found that Macrotermes michaelseni detected a virulent isolate of Metarhizium anisopliae from some distance and avoided direct physical contact. We hypothesized that there may be a relationship between virulence and repellency of different isolates of M. anisopliae and Beauveria bassiana to the termite. We compared these for selected isolates of the two fungi. Positive correlations between the two parameters for both sets of isolates of the fungi were obtained. The results show an interesting co-evolutionary phenomenon in which the termite's response to either M. anisopliae or B. bassiana is directly related to potential harm these fungi can inflict on the insect and that the virulent strains are more likely to be recognized from some distance and avoided.

The results and insights from recent research on the chemical ecology of polymorphic acridids are reviewed. Many of the new findings come from studies on the desert locust, Schistocerca gregaria, which has continued to be the primary research insect in most laboratories. Earlier confusion between stimuli associated with phase change and social cohesion has been resolved. The roles of chemotactile and olfactory cues together with tactile and visual stimuli in key locust processes, comprising gregarization, social cohesion, synchronous maturation, mating, oviposition, and maternal transfer of gregarious character, are better understood. Some of the key pheromones of the gregarious phase have been characterized. Chemical communication is also shown to be important in the life style of the solitarious phase. The behavioral pattern and responses of this phase reflect a strong propensity of the species to exploit opportunities under appropriate conditions to form or join the crowd and to gregarize. Outstanding questions are highlighted.

FemaleCotesia flavipes Cameron andCotesia sesamiae (Cameron) were attracted to odors in a Y-tube olfactometer from uninfested maize (Zea mays L.), sorghum [Sorghum bicolor (L.)], and napier grass (Pennisetum purpureum Schumach). In dual choice tests,Cotesia flavipes showed a preference for maize over sorghum, while maize and napier grass were equally attractive. In contrast,Cotesia sesamiae preferred volatiles from sorghum and napier grass over those from maize. The two parasitoids were significantly more attracted to maize infested with the stemborers,Chilo partellus (Swinhoe),Chilo orichalcociliellus Strand,Sesamia calamistis Hampson, andBusseola fusca (Fuller), than uninfested maize. In dual choice tests,Cotesia flavipes andCotesia sesamiae were unable to discriminate between odors from plants infested by the different species of stemborers.

Hexanal, octanal, nonanal, decanal, hexanoic acid, octanoic acid, nonanoic acid, and decanoic acid were identified in the volatile emissions from fifth instars ofSchistocerca gregaria by coupled gas chromatography-electroantennography (GC-EAD) detection and coupled GC-mass spectrometry (MS). In laboratory assays, synthetic blends of the eight compounds, with acids and aldehydes tested separately, evoked strong aggregation responses from fifth instars, similar to responses evoked by a crude volatile extract of the nymphs. A nymphal fecal volatile phenolic blend of guaiacol and phenol, which we have previously shown to evoke an aggregative response from different stages of the insect, significantly synergized the activity of the blend of eight compounds, suggesting mutually augmentative roles for nymphal and fecal volatiles in evoking aggregation. These results indicate that the aggregation behavior of gregarious second to fifth instars is modulated by three sets of pheromonal compounds: aldehydes and acids emitted by the nymphs themselves and phenols associated with their feces.