An airflow olfactometer for measuring olfactory responses of hymenopterous parasitoids and other small insects

ABSTRACT. A new type of airflow olfactometer is described, and results given of experiments using it to measure behavioural olfactory responses of hymenopterous parasitoids. Compared with Y-tube olfactometers it shows several advantages. In its exposure chamber four separate abutting odour fields are presented so that the test insect can readily enter and re-enter them. More than one odour (or different concentrations of one odour) can be tested at the same time, thereby providing complex preference test situations. The various behavioural measures that can be assessed in the apparatus are examined and discussed.     

Oviposition by the African migratory locust, Locusta migratoria migratorioides, in a crop environment in South Africa

Oviposition by the African migratory locust, Locusta migratoria migratorioides (Orthoptera: Acrididae), was studied in maize and wheat crops on the Orange Free State Highveld. Maize was shown to be the most important oviposition habitat with peak laying taking place in autumn and early winter when highest pod densities were recorded. Laying was mainly concentrated along the middle of the crop interrows in maize and within clearings in the wheat crop. Despite the uniform layout of these crops, the distribution of egg pods was found to be aggregated. Non-reproductive behaviour, such as locust aggregation, basking and feeding, as well as environmental factors appeared to influence the distribution of egg pods in these crops. Secondary selection for optinum soil moisture and compaction on the laying site enhanced the aggregation of pods.     

Comb cutting inRopalidia plebeiana: a new process of colony fission in social wasps (Hymenoptera: Vespidae)

Summary Females of an Australian polistine wasp,Ropalidia plebeiana, often use their mandibles to cut their nest-comb in spring, dividing it into two or more completely independent nests. Prior to the division, each of the major egg layers, often with some subordinates, tended to occupy a different part of a single comb. These females gnawed cells in the intermediate zone between such territories, and ultimately divided the comb. Many other females also built new nests near the nest aggregations, but addition of new nests by comb cutting represented 34.8 % of the increase in nest number. This method of colony fission is so far unknown in any eusocial Hymenoptera.     

An odd activity of an ant (Cataglyphis bicolor); ≪visiting≫

Summary An unexplained form of behaviour connecting nests of an antCataglyphis bicolor F. is described. Individuals from one nest visit another wandering around the nest entrance, for periods of up to half an hour or more. Their behaviour is quite distinct from any seen in normal foraging. These individuals come from the upper end of the range of size; more frequently but not always from a larger to a smaller nest. Nests are normally antagonistic. These ants back away rapidly from an ant of the nest visited.     

The influence of azadirachtin on the feeding behaviour of cereal aphids and slugs

The probing behaviour of Rhopalosiphum padi (L.) and Sitobion avenae (F.) and the feeding behaviour of several slug species, (Deroceras reticulatum (Müller), Arion distinctus Mabille, Agriolimax caruanae Pollonera, Maximus sp.) were assessed on seedlings of winter barley (Hordeum marinum) treated with different concentrations of azadirachtin. Settling behaviour of both aphid species was strongly biased towards the untreated seedlings or those treated with low concentrations of azadirachtin. Concentrations of <500 ppm were effective with topical application and probing activity was reduced for at least 4 days after application. Systemic activity of azadirachtin against cereal aphids was also demonstrated. Feeding behaviour of the slug species, as seen by the amount of leaf eaten compared to the controls, was not affected by the presence of azadirachtin at those concentrations which deterred aphids from feeding. The relevance of these results to crop protection is discussed.     

Comparison of learning in related generalist and specialist eucoilid parasitoids

Effects of learning in two microhabitat specialists, Leptopilina boulardia Barbotin et al. and L. fimbriata Kieffer were compared to previous and new results of learning in the microhabitat generalist L. heterotoma Thomson. Females were given one or more oviposition experiences on hosts in different types of substrate. In all species oviposition experience affected the choice for a substrate, although this effect of learning was considerably less in L. fimbriata compared to the other two species. Patch times, known to be highly determined by experience in the generalist L. heterotoma, were much less flexible in the specialists. L. boulardi and L. fimbriata have fixed patch times on their natural substrate and have variable patch times on other substrates only. In all three species one oviposition affected the choice for a substrate. Additional ovipositions showed no different effect. An accumulative effect of the number of ovipositions on patch times was found in L. heterotoma only. Retention of the learning effect was only studied in L. boulardi, and was shown to be similar to that reported for L. heterotoma, i.e. two to three days. Although learning was found in both the generalist and the specialist species studied, it seems to affect their foraging behaviour differently.     

The use of genetic marking to assess the reproductive success of mature male Atlantic salmon parr (Salmo salar, L.) under natural spawning conditions

The reproductive success of mature male Atlantic salmon parr ( Salmo salar ) under natural spawning conditions was estimated using the polymorphism at the MEP - 2 * locus as a genetic marker. The percentage of eggs per redd fertilized by parr varied considerably over the five redds examined (0·9–27.7%, mean 10·8%), but a gametic contribution from mature parr was detected in each case. Parr reproductive success has important implications for the population structure and evolution of the Atlantic salmon through its effect on gene flow.     

Foraging behavior of specialist and generalist caterpillars on plantain (Plantago lanceolata) altered by predatory stinkbugs

Summary To examine the effects of predators and plant genotype on the behavior, patterns of herbivory, growth and survivorship of caterpillars, we used an experimental garden in which we contrasted two hostplant genotypes of plantain (Plantago lanceolata), two kinds of herbivores (specialist Junonia coenia vs. generalist Pyrrharctia isabella) and two levels of caterpillar predation (with and without Podisus maculiventris stinkbugs). Each of the replicate plots per treatment contained two plants of the same genotype. The stinkbugs reduced the survivorship of the specialist caterpillars but not that of the generalists, which reflects the differences in predatoravoidance behaviors of these species. Nonetheless, the stinkbugs influenced the behavior of both caterpillar species. When stinkbugs were present, both specialist and generalist caterpillars were less likely to be found on the plant upon which they were initially placed (=initial plant), and they were more likely to be off both plants within the plot than larvae in the absence of predators. Consequently in the presence of the stinkbug predators, the proportion of the initial plants consumed was less than in the absence of the predators. Plant genotype influenced plant size and the proportion of individual plants eaten, but it did not affect larval location on the plots. Neither presence of predators nor plant genotype had an effect on relative growth rate of the caterpillars.     

The influence of plant architecture on the foraging efficiencies of a suite of ladybird beetles feeding on aphids

By manipulating plant variety and predator species, we investigated the interactions of plant and predator traits in determining predation effectiveness. The predators were all coccinellid adults (Hippodamia convergens, Hippodamia variegata, Coccinella apunctata, and Coccinella septempunctata) and the prey were cabbage aphids (Brevicoryne brassicae). Foraging behavior of the four predators was observed on four crucifers that differed widely in their structures and surface textures (Brassica oleracea caulorapa, Brassica campestris, Brassica juncea crispifolia, and Hirschfeldia incana). Predation rates were significantly influenced by plant variety, a result we attribute to direct effects of plant morphology on predator mobility, falling frequency, and prey accessibility. Predation rates did not vary significantly among the ladybirds, although the four species did exhibit distinct foraging strategies as measured by time spent actively foraging, the rate of encountering aphids, and the fraction of aphids encountered that were consumed. The coccinellids also differed in their propensity for flying away from the plant, and in the frequency with which they fell from the plant. We did not detect any significant interaction effects between plant and predator species, suggesting that the main effects of plant and predator species may overwhelm their interactions in this kind of system. Our results suggest that the level of predation upon herbivorous insects may depend more upon plant architecture than on the particular species of natural enemies present.