Do anthocorid predators respond to synomones from Psylla-infested pear trees under field conditions?

Because Y-tube olfactometer experiments in the laboratory showed a response of anthocorid bugs to odour fromPsylla-infested leaves, it was of interest to assess its relevance under field circumstances. This was done by measuring the density of predatory bugs on pear trees adjacent toPsylla-infested or control trees that were covered with fine mesh gauze-screens. In this way odours from these caged trees could spread through the screen, while contact with thePsylla prey in the cage was prevented. The density of anthocorid predators around cages with heavily infested trees was significantly higher than around uncaged control trees and around cages containing uninfested or little infested trees. Covering a cage withPsylla-infested trees by an airtight plastic sheet led to an immediate drop in the density of anthocorid predators, whereas removal of the sheet led to predator aggregation again. The results of these field experiments strongly support the hypothesis that anthocorid predators respond to volatile chemicals emanating fromPsylla-infested pear trees.     

烟粉虱B生物型若虫、皮蜕及成虫提取物对双斑蚜小蜂行为的影响

烟粉虱B生物型的若虫、皮蜕及其成虫的提取物作为一种利它素信息源,在室内对其在双斑蚜小蜂寻找寄主取食、寄生行为的影响进行了生物测定。烟粉虱的若虫、皮蜕及其成虫分别用正己烷、乙醇和无菌水进行粗提。研究结果发现,双斑蚜小蜂在处理区寻找寄主停留的时间高于对照区。在处理区,双斑蚜小蜂行动活泼,对利它素源表现出高的正趋向性和选择性。对于同一利它素源、同一提取介质的两种不同浓度,双斑蚜小蜂在若虫 水提取物的高浓度区停留的时间（111.23s）最长,与在低浓度区的停留时间差异显著;而在烟粉虱皮蜕及其成虫的水、正己烷和乙醇提取物处理区,不同浓度的提取物对蚜小蜂停留的时间影响差异不显著。本研究的结果表明,利它素可以增加蚜小蜂寻找寄主的效率,有利于蚜小蜂寻找到适宜的寄主。     

Characterization of restricted area searching behavior following consumption of prey and non-prey food in a cursorial spider, Hibana futilis

Cursorial spiders are important predators of crop pests in a variety of agricultural systems. Their survivorship, growth, and fecundity can be enhanced by the consumption of extra‐floral nectar. We recently showed that Hibana futilis (Banks) (Araneae: Anyphaenidae) engages in restricted area search following contact with nectar, is stimulated by nectar aroma, and can learn to recognize novel aroma cues. Studies have shown that H. futilis is also responsive to solvent extracts of the eggs and scales of the corn earworm, Helicoverpa zea Boddie (Lepidoptera: Noctuidae), one of its primary prey insects in cotton. The arrestment behavior of cursorial spiders following consumption of prey and non‐prey food has not been characterized. In the present study, the responses of spiders were measured following consumption of prey (H. zea eggs) or non‐prey (droplets of dilute honey) food items and compared with individuals tested without food items. The food items were presented to the spiders in test arenas constructed from the top of an inverted glass Petri dish cover. A combination of real time and recorded observations were made via a video camera attached to a computer. The behaviors and movement patterns of individual spiders were analyzed with behavioral tracking software. Significant differences in the behaviors and motion paths of spiders tested in the different treatments were observed. Hibana futilis displayed significantly more dispersal behavior on a blank test arena, than on test arenas supplied with honey droplets or moth eggs. Likewise, spiders tested on the blank arena crawled faster and their motion paths were significantly less tortuous than those of spiders tested in the arenas with honey or moth eggs. Following consumption of both the honey droplets and moth eggs, spiders showed elevated levels of restricted area search and lowered levels of dispersal behavior. The analysis showed that these spiders could crawl rapidly for extended distances. Behaviors such as restricted area search and learned recognition of food‐based stimuli would facilitate efficient location of the food resources needed to maintain their high activity levels.     

Measuring host finding capacity and arrestment of natural enemies of the cassava mealybug,Phenacoccus manihoti, in the field

In unifested fields, 80 cassava tips were artificially infested with 0, 1, 2, 4, 8, 16, 32, or 64 third instars, and 20 or 100 eggs of cassava mealybug,Phenacoccus manihoti Matile-Ferrero (Hom., Pseudococcidae). Another 80 uninfested tips served as a control. Tips were arranged in a circle of 28 m diameter, in the centre of which the following exotic natural enemies ofP. manihoti were released:Apoanagyrus (Epidinocarsis) lopezi De Santis andA. diversicornis (Howard) (Hym., Encyrtidae),Hyperaspis notata (Mulsant) andDiomus hennesseyi Fürsch (Col., Coccinellidae), and others. This experiment was repeated six times. During the 4–14 days following release, all experimental tips were inspected at two-hour intervals during each day and the presence of exotic as well as indigenous natural enemies, likeExochomus troberti Mulsant (Col., Coccinellidae), ants and spiders was noted. The experiment was repeated six times measured the aggregative response by the natural enemies to different host densities, achieved through host attractance and arrestment. All exotic natural enemies, except the males ofApoanagyrus spp., were fast attracted to the host colonies. As compared to the control tips, they concentrated on the infested tips about 50-fold for the twoApoanagyrus spp. and 10 to 20-fold for the exotic coccinellids. By contrast, non-coevolved indigenous coccinellids, as well as generalist predators like ants and spiders were attracted to the infested tips only 2 to 5-fold.A. lopezi responded best to different host densities, followed byA. diversicornis and the coccinellids, followed by ants and spiders. None of the parasitoids or predators was particularly attracted to egg masses. These results correspond closely to the known efficiencies of these natural enemies,A. lopezi standing out among all candidates. The results of such aggregation studies are compared with those of life-table studies.     

Evidence for male- and juvenile-specific contact pheromones of the common bed bug Cimex lectularius

Males and females of the common bed bug, Cimex lectularius L. (Heteroptera: Cimicidae), have been shown to produce and respond to an aggregation pheromone. We tested whether juvenile C. lectularius also produce and respond to aggregation pheromone, and whether the pheromone is perceived by contact chemoreception. In dual‐choice laboratory experiments, juveniles, but not males or females, preferred juvenile‐exposed paper discs to control discs. Unlike juveniles, males and females preferred male‐exposed paper discs to control discs. Neither juveniles, males, nor females preferred female‐exposed discs to control discs. When test stimuli were inaccessible, C. lectularius failed to show any preference. Male‐ and juvenile‐specific contact pheromones may have contrasting functions of marking shelters as safe refugia for development and growth (juveniles) or mate encounter (adults), but result in the same phenomenon, the aggregation of conspecifics.     

截形叶螨对胡瓜钝绥螨的吸引作用

室内测定表明,截形叶螨不同螨态对胡瓜钝绥螨均有显著的吸引作用,均达到极显著水平,而胡瓜钝绥螨对截形叶螨的排泄物没有明显的反应。截形叶螨对胡瓜钝绥螨的这种吸引作用说明胡瓜钝绥螨具有自动搜索截形叶螨的能力,表明胡瓜钝绥螨可以用于截形叶螨的生物防治。     

Synergism in the Oviposition Behavior of Plutella xylostella: Sinigrin and Wax Compounds

Diamondback moth, Plutella xylostella, host examining and oviposition behaviors were measured in response to sinigrin dosages (10 ^–3 , 10 ^–4 , and 10 ^–5 M) and controls with and without the addition of n-alkanes. Individual females were presented with a treatment and videotaped while an observer documented specific behaviors during 5-min observation periods. Behavior in response to sinigrin alone was not significantly different from that in response to controls. Alkane alone significantly reduced movement rate during treatment contact, but did not significantly affect other behaviors. Sinigrin concentrations combined with alkane significantly slowed the rate of insect movement, increased turning, and led to significantly longer treatment encounter durations. Behavior changes in response to sinigrin + alkane increased insect exposure to the sinigrin concentrations and led to greater oviposition compared to that in response to sinigrin treatments alone. The synergistic effect that mixing sinigrin and alkane has on P. xylostella behavior arises because the additional time females spend in contact with the treatment increases the rate at which they experience the available stimuli. Involvement of the antennae during examining of a treatment, referred to as swabbing, was usually associated with oviposition on alkane-coated sinigrin treatments. The presence of alkane may alter the way sinigrin is perceived. Oviposition in response to the treatment combinations was also tested in overnight bioassays. The pattern of oviposition in response to treatments during bioassays differed from that established during observations. The value of direct observations and the mechanistic interpretations they allow are emphasized.     

Do Herbivore-Induced Plant Volatiles Influence Predator Migration and Local Dynamics of Herbivorous and Predatory Mites?

If predators lack information on the prey's position, prey have more chance to escape predation and will therefore reach higher population densities. One of the many possible cues that predators may use to find their prey are herbivore-induced plant volatiles. Although their effects on the behaviour of foraging predators have been well studied, little is known about how these prey-related odours affect predator–prey dynamics on a plant. We hypothesise that herbivore-induced plant volatiles provide the major cue eliciting predator arrestment on prey-infested leaves and that the response to these volatiles ultimately leads to lower prey densities. To test this hypothesis experimentally, we created two types of odour-saturated environments: one with herbivore-induced plant volatiles (treatment), and one with green-leaf volatiles (control). An odour-free environment could not be tested because herbivores require plants for population growth. We measured the rate at which predatory mites (Phytoseiulus persimilis) immigrate, emigrate and exploit a single leaf infested by two-spotted spider mites (Tetranychus urticae). The experiments did not show a significant difference between treatment and control. At best, there was a somewhat higher rate of predator (and possibly also prey) emigration in the treatment. The lack of a pronounced difference between treatment and control indicates that at the spatial scale of the experiments random searching for prey was as effective as directional searching. Alternatively, predators were arrested in the prey patch by responding not merely to herbivore-induced plant volatiles, but also to other prey-related cues, such as web and faeces. Based on our current experience we advocate to increase the spatial scale of the experiment (>1m²) and we provide other suggestions for improving the set-up.     

Relationship between sex pheromone elicited behaviour and response of single olfactory receptor neurones in a wind tunnel

Responses from pheromone‐specific receptor neurones in male Agrotis segetum (Denis & Schiffermüller) (Lepidoptera: Noctuidae) were recorded in a laboratory wind tunnel. Stimuli were: (1) rubber septum dispensers loaded with single components or a four‐component pheromone blend, (2) excised glands from female A. segetum, (3) constrained A. segetum females with extruded glands. Dose–response curves for three neurone‐types with different specificity were established. The neurones were specifically tuned to respond to either one of the two pheromone components (Z)‐5‐decenyl acetate and (Z)‐7‐dodecenyl acetate, or to the behavioural antagonist (Z)‐5‐decenol. In parallel, a behavioural dose–response curve with males flying upwind to a four‐component pheromone blend was established. There was a clear correlation between behavioural arrestment of upwind flight and maximum spiking activity in Z5–10:OAc‐specific neurones. The pheromone release rates of individual females and synthetic dispensers were compared. A load of 50–200 ng of Z5–10:OAc on a rubber septum elicited approximately the same neural response as one female gland.     

Emergence,dispersal, and mate finding via a substrate‐borne sex pheromone in the parasitoid Metaphycus luteolus

Metaphycus luteolus Timberlake (Hymenoptera: Encyrtidae) is a facultatively gregarious parasitoid of soft scale insects. We conducted behavioral experiments to better understand the mating structure of this species. Emergence of male and female offspring is synchronized, beginning at the onset of photoperiod. Both sexes are able to disperse, although dispersal of males from natal patches appears to take longer than dispersal of females. We demonstrated the presence of a female‐produced contact pheromone using open arena bioassays and motion tracking software, testing residues deposited by walking females, and extracts of females. Males responded to the females' ‘chemical footprints’ and to acetone and hexane extracts of females by searching and arrestment on the chemical residues. Responses of males were dose dependent and diminished with time since the stimulus was deposited. Our findings support the hypothesis that non‐local mating among wasps emerging from different hosts may be quite common in these parasitoids. The implications of our results for the mating structure and previously documented sex ratio patterns of these parasitoids are described.