Patch choice from a distance and use of habitat information during foraging by the parasitoid Ibalia leucospoides

1. In environments in which resources are distributed heterogeneously, patch choice and the length of time spent on a patch by foragers are subject to strong selective pressures. This is particularly true for parasitoids because their host foraging success translates directly into individual fitness. 2. The aim of this study was to test whether: (i) females of the parasitoid Ibalia leucospoides (Hymenoptera: Ibaliidae) can discriminate among patches according to host numbers; (ii) the surrounding context affects the initial choice of patch, as well as time spent on patch; and (iii) the perceived quality of a given patch is affected by the quality of the surrounding patches. 3. Each female was randomly exposed to one of three different three‐patch environments which differed in host number per patch, mean environment host number and host distribution among patches. For each treatment level, the first patch chosen and the time allocated to each patch visited by the female were recorded. 4. Females of I. leucospoides were able to discriminate different levels of host numbers among patches from a distance. The patch bearing the highest number of hosts was, predominantly, the first choice. Patch host number in association with mean habitat profitability influenced the length of time spent on the first patch visited. By contrast, variance in habitat profitability did not influence time allocation decisions. Contrary to the study prediction, there were no significant habitat‐dependent time allocation differences among patches holding the same number of hosts. 5. The results indicate that, for I. leucospoides, patch exploitation decisions are partially influenced by information obtained from the habitat as a whole, a behaviour that may prove to indicate adaptive ability in highly patchy environments, as well as suggesting the presence of good cognitive abilities in this parasitoid species.     

Sequence data reflect the introduction pathways of the Sirex woodwasp parasitoid,Ibalia leucospoides (Ibaliidae,Hymenoptera)

1. The parasitoid wasp Ibalia leucospoides is native to the northern hemisphere and has been introduced to the southern hemisphere as a biological control agent for the invasive woodwasp Sirex noctilio. Two subspecies of the parasitoid, Ibalia leucospoides leucospoides (Palearctic distribution) and Ibalia leucospoides ensiger (Nearctic distribution), were introduced and are reported to have hybridized.
2. Despite extensive records of the numbers and origins of the wasps imported into the southern hemisphere, nothing is known regarding their current population diversity. We investigated the genetic variation of I. leucospoides in its native and introduced ranges using mitochondrial (COI) and nuclear (ITS) markers.
3. Mitochondrial DNA diversity in the introduced range was limited, with only five haplotypes, although sequence divergence between these haplotypes was high. Similarly, the ITS rDNA sequences revealed multiple clades present in the introduced range.
4. These results reflect introductions from a wide geographical range but where genetic bottlenecks have possibly reduced the genetic diversity. The data further reflect the origin of the I. leucospoides populations in South America and South Africa from New Zealand or Australia. We found no evidence of hybridization between the two subspecies of the parasitoid in its introduced range, and no evidence that I. leucospoides ensiger has established outside its native range.

     

Flight potential of <Emphasis Type="Italic">Microplitis mediator</Emphasis>, a parasitoid of various lepidopteran pests

The efficacy of using natural enemies to control pests under field conditions largely depends on their mobility and, more specifically, on their capacity to quickly locate pest infestation. For many natural enemies, for example parasitoids, mobility is directly related to flight aptitude, which is determined by the capacity and inclination of a species to engage in flight. In this study, we determined the various factors that affected flight performance of Microplitis mediator (Haliday) (Hymenoptera: Braconidae), using a computer-monitored flight mill. No differences were found in flight performance (i.e., flight distance, duration, speed) between both sexes of M. mediator, and flight capacity increased up to an age of 5–7 days followed by a gradual decline afterwards. For one-day-old female parasitoids, mean (±SE) flight distance and duration were 6.23 ± 0.88 km and 85.15 ± 14.44 min, respectively, with a maximum flight distance of 18.0 km. For male parasitoids, mean flight distance and duration were 5.27 ± 0.51 km and 85.74 ± 7.63 min, respectively. Mating status did not affect flight performance of males, while flight distance of four-day-old ovipositing M. mediator females was much lower than that of un-mated females of the same age. Un-mated adults flew most actively at 22–24°C and inclination to fly gradually declined with decreasing temperature. Temperatures above 26°C considerably reduced flight activity of M. mediator. Wasps engaged in normal flight under a broad range of relative humidity (RH) conditions, with an optimum RH range identified as 75–90%. Our research shows that M. mediator is a highly active parasitoid, because both sexes show great inclination to fly under a range of environmental conditions and flight capacity at different ages. Our results can help explain parasitoid performance in the field and provide baseline information to help guide augmentative releases. Handling editor: Dirk Babendreier.     

Patch Time Allocation by a Parasitoid: The Influence of Con-specifics,Host Abundance and Distance to the Patch

Patch residence time is at the core of models of decision making by foragers living in patchy environments. We studied patch residence time (PRT) of Ibalia leucospoides, a parasitoid of the woodwasp Sirex noctilio, as assigned to 4 treatments (recent feeding and/or oviposition experience) foraging in an array of host-infested pine logs. We tested the effects of distance from release point, host abundance, and the number of con-specifics at the time of arrival, on patch (pine log) residence time. PRT depended on a combination of patch quality (number of hosts in a log) and distance from the release point. Neither the presence of con-specifics on the patch, prior exposure to hosts, nor feeding prior to the experiment affected the time spent on a patch. We conclude that PRT in I. leucospoides meets Marginal Value Theorem predictions qualitatively, overruling the effects recent oviposition experience, access to food and contact with conspecifics. These findings are in line with the reported pro-ovigeny in I. leucospoides as well as the strong spatial aggregation of hosts in the field.     

Sex,life history and morphology drive individual variation in flight performance of an insect parasitoid

1. The movement of organisms can be driven by multiple factors and has implications for fitness and the spatial distribution of populations. Insects spend a large proportion of their adult lives foraging by flying for resources; however, their capability and motivation to move can vary across individuals. 2. The aims of this study were to examine interindividual and sex differences in flight performance and flight characteristics, using a flight mill bioassay, in Megarhyssa nortoni (Hymenoptera; Ichneumonidae), a parasitoid of the invasive woodwasp Sirex noctilio (Hymenoptera: Siricidae), one of the most important pests of pine afforestation worldwide. We also assessed the influence of morphological traits in combination with sex on flight and explored the cost of flight on longevity and mass loss. 3. The results show a difference between sexes in flight characteristics and performance. Females show greater total distance flown than males, and have a better capacity to undergo sustained flight. Sexual size dimorphism was also found and it was noted that size positively affects distances travelled. Females have a longer life span than males, yet no differences were noted in longevity within sex between individuals that did not fly and those that flew. Age did not influence flight performance of females or impacted on post‐flight longevity. Females lost less body mass than males even after flying longer distances. 4. These results suggest that sex‐specific behaviours probably govern flight abilities together with (and not only because of) morphological traits. The paper discusses sex‐specific life‐history strategies in parasitoids and their implications for biocontrol programmes.     

Factors influencing the dispersal of a native parasitoid, <Emphasis Type="Italic">Phasgonophora sulcata</Emphasis>, attacking the emerald ash borer: implications for biological control

High parasitism by a native parasitoid, Phasgonophora sulcata Westwood (Hymenoptera: Chalcididae), has been reported on emerald ash borer (hereafter EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), in North America. Use of this parasitoid in an augmentative biological control program has been proposed to slow the spread of EAB, yet information is lacking on key aspects of this parasitoid’s dispersal. We document the flight capacity and walking activity of P. sulcata, its potential fecundity, and describe how age, body size, temperature, and time of day affect these parameters. Wasp flight capacity, measured using flight mills, increased with temperature and decreased with age. Unexpectedly, age and body size did not affect wasp walking activity, and we saw no relationship between walking activity and flight capacity. Older wasps had lower potential fecundity than younger wasps. These results suggest that P. sulcata should be released as pupae near EAB-infested ash trees to improve efficacy and potential biological control success.     

Effect of parasitism on flight behavior of the soybean aphid, Aphis glycines

Many aphid species possess wingless (apterous) and winged (alate) stages, both of which can harbor parasitoids at various developmental stages. Alates can either be parasitized directly or can bear parasitoids eggs or larvae resulting from prior parasitism of alatoid nymphs. Winged aphids bearing parasitoid eggs or young larvae eventually still engage in long-distance flights, thereby facilitating parasitoid dispersal. This may have a number of important implications for biological control of aphids by parasitoids. In this study, we determined the effect of parasitism by Aphelinus varipes (Hymenoptera: Aphelinidae) on wing development and flight of the soybean aphid, Aphis glycines (Hemiptera: Aphididae). We also quantified the influence of aphid flight distance on subsequent A. varipes development. Parasitism by A. varipes was allowed at different A. glycines developmental stages (i.e., alatoid 3rd and 4th-instar nymphs, alates) and subsequent aphid flight was measured using a computer-monitored flight mill. Only 35% of aphids parasitized as L3 alatoid nymphs produced normal winged adults compared to 100% of L4 alatoids. Flight performance of aphids parasitized as 4th-instar alatoid nymphs 24 or 48 h prior to testing was similar to that of un-parasitized alates of identical age, but declined sharply for alates that had been parasitized as 4th-instar alatoid nymphs 72 and 96 h prior to testing. Flight performance of aphids parasitized as alate adults for 24 h was not significantly different from un-parasitized alates of comparable ages. Flight distance did not affect parasitoid larval or pupal development times, or the percent mummification of parasitized aphids. Our results have implications for natural biological control of A. glycines in Asia and classical biological control of the soybean aphid in North America.     

Effects of Wind Speed and Atmospheric Pressure on Mate Searching Behavior in the Aphid Parasitoid Aphidius nigripes (Hymenoptera: Aphidiidae)

The effects of wind speed and atmospheric pressure on male mate searching behavior, modulated by a female sex pheromone, were investigated in the aphid parasitoid Aphidius nigripes (Hymenoptera: Aphidiidae). Male A. nigripe generally did not reach females at wind speeds of 100 cm/sec, as the majority of individuals taking flight in the pheromone plume (81.8%) were unable to sustain upwind flight. At lower wind velocities, male responsiveness to females generally decreased with distance from the source. However, wind speeds approaching the upper threshold (100 cm/sec) tended to eliminate this distance effect. Therefore, there appears to be a trade-off between the need for higher wind speeds to detect the pheromone source from long distances, and a reduction in male flight capacity as wind velocity increases. Our results also indicate that chemical communication in A. nigripes could be affected by variations in atmospheric pressure, as we observed a relationship between pressure fluctuations in the 24 hr prior to testing and male responsiveness to females. The importance of these abiotic factors on mate searching behavior is discussed within the context of the reproductive biology of A. nigripes.     

Winter and spring ecology of <Emphasis Type="Italic">Anaphes nitens</Emphasis>, a solitary egg-parasitoid of the <Emphasis Type="Italic">Eucalyptus</Emphasis> snout-beetle <Emphasis Type="Italic">Gonipterus scutellatus</Emphasis>

We investigated the effects of temperature, photoperiod, food and host availability, and body size on the overwintering abilities of the egg parasitoid Anaphes nitens Girault (Hymenoptera, Mymaridae) under natural conditions. Seven groups of eighty females received one of four treatments (n = 20): (i) honey and hosts, (ii) water and hosts, (iii) honey, or (iv) water. Seven groups of forty males received only honey or water (n = 20). To test if short day-length is the main cue for larval dormancy, the experiment was replicated inside a climate chamber at 20°C and under a winter photoperiod. A. nitens overwinters because of quiescence or oligopause inside the hosts and increased adult longevity. Mean pre-emergence mortality was up to 26% indoors and 15.2% outdoors, males being more affected. Development time had a significant and positive effect on body size. Honey-fed females without hosts had the highest longevity (53 days). Mother’s diet and size affected development time, body size, longevity, and fecundity of the progeny. The results confirm the good adaptation of the parasitoid to the environmental conditions of NW Spain and its ability to synchronize its life cycle with the phenology of the host. Handling editor: Drik Babendreier.     

Life history studies of <Emphasis Type="Italic">Prorops nasuta</Emphasis>, a parasitoid of the coffee berry borer

Life history studies were conducted in the laboratory on the African parasitoid Prorops nasuta Waterston (Hymenoptera: Bethylidae), a parasitoid of the coffee berry borer, Hypothenemus hampei (Ferrari) (Coleoptera: Scolytidae). The female wasp enters an infested coffee berry, kills the adult borer and seals the entrance of the berry with the body of the borer, impeding the entry of other organisms into the berry. The preoviposition period ranges from 3 to 14 days (mean 5.42 ± 0.37 SE). During this time females feed on the immature stages and paralyse fully grown larvae and pupae of the CBB. P. nasuta is an idiobiont solitary ectoparasitoid. Eggs are laid externally on the last instar larvae and pupae. Mean development time (egg to adult) for males and females was 27.7 (±0.37 SE) and 30 (±0.12 SE) days, respectively. Median survival for wasps fed on final instar CBB larvae was 27.7 days, significantly longer than any other treatment, while for females without food it was 2.5 days. In culture, females produced an average of 4.3 (±0.39 SE) progeny during their lifetimes. Adults began emerging at 30.6 days (±0.28 SE) after cultures were started and peak production was reached at 36 days, declining thereafter. Males normally emerged from coffee beans 2–3 days before females. Males usually emerged from 07:00 to 09:00h and females from 10:00 to 14:00 h. The culture sex ratio (proportion of males) was 0.21. Virgin females produced only male offspring.     

Size‐dependent insect flight energetics at different sugar supplies

Under most circumstances, large body size confers a higher fitness and is positively selected, whereas selection against large size is empirically poorly documented. Physiologically, according to the ¾ power law, larger animals have lower relative but higher absolute energy demands, such that large body size may become disadvantageous, particularly under fast locomotion in food‐limited environments. After a period of initial feeding on different sugar concentrations, we investigated size‐dependent energy content (reserves) at baseline and of females unflown (i.e. resting) or flown for 18 h in two (replicate) insect species: the yellow dung fly Scathophaga stercoraria and the yellow fever mosquito Aedes aegypti. Tethered adults of various sizes were tested in a flight mill. In both species, teneral glycogen, sugar, and lipid content increased with sugar availability, and isometrically or even hyper‐allometrically (slope > 1) with body size. Activity treatment also revealed the expected consumption effects. Both species increased their flight distance with sugar supply, although only larger mosquitoes flew longer. Crucially, larger females of both species disproportionately exhausted more glycogen and sugars (but not lipid) during flight. The mosquitoes appeared to adjust their flight more finely to their size‐dependent energy reserves at all sugar availabilities, whereas, in the dung flies, size‐dependent energy demands were detectable only with a low but not with an overly high sugar supply. Although we found a greater absolute and relative locomotory energy demand for the larger flies, which is in agreement with interspecific patterns in insects, this was (more than) compensated by their greater baseline energy reserves, resulting in the greater net flying capacity of larger individuals. Consequently, we found no evidence for energetic mechanisms limiting the performance of large flying insects under food limitation. The differences between the two species presumably relate to mosquitoes inherently being long distance flyers and dung flies being short distance flyers. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ●● , ●●–●●.     

Parasitism and dispersal potential of Sirex noctilio: implications for biological control

1 Sirex noctilio F. (Hymenoptera: Siricidae) is a wood‐boring wasp that attacks many pine species, including commercial trees planted throughout the world. Management of its populations is largely based on biological control using the nematode Beddingia siricidicola. Adult females are sterilized by the nematode, but are free to move and attack new trees, promoting nematode dispersal. Although generally successful, wasp management through nematode introductions has sometimes been inadequate. 2 We evaluated the effect of parasitism by B. siricidicola on flight performance of woodwasps under laboratory conditions. Using flight mills, we recorded a total of 46 flight trials over 23 h, obtained from infected and control (uninfected) females. 3 Although all wasps lost weight during flight, parasitized females were significantly smaller and suffered larger weight losses than uninfected females. In addition, total flight distance and velocity were lower in parasitized females. 4 Because nematode infection transmission relies on healthy wasps attacking trees previously visited by nematode‐bearing females, differential dispersal capacity could limit biological control success.     

A double-edged sword: Amylostereum areolatum odors attract both Sirex noctilio (Hymenoptera: Siricidae) and its parasitoid,Ibalia leucospoides

The Eurasian woodwasp, Sirex noctilio, is an invasive pest of pines in temperate regions of the Southern Hemisphere, and has been introduced to North America. A parasitoid, Ibalia leucospoides, has been broadly employed for biological control of this pest. Volatiles emitted from the fungal symbiont of S. noctilio, Amylostereum areolatum, are reliable cues for S. noctilio and I. leucospoides females to optimize their foraging behavior (host location and host habitat finding) in a chemically complex environment. The headspace volatiles of A. areolatum, were analyzed using coupled gas chromatography-mass spectrometry (GC-MS) and GC-electroantennographic detection (GC-EAD) for both S. noctilio and I. leucospoides females. Analyses revealed that both species could detect several fungal volatiles. In olfactometer bioassays, S. noctilio females were attracted to a 4-component blend of 6-methyl-5-hepten-2-one, trans-3-hexenyl acetate, linalool, and geraniol, while the addition of ρ-anisaldehyde to the blend was necessary for attraction of I. leucospoides females. The results of trap catches in field experiments confirmed that these fungal volatiles in combination with host tree volatiles are attractive to both species, although the release rate of the fungal volatiles is important. These volatiles can serve as a basis for the development of improved lures for both species.     

Evidence for acoustic communication in the parasitoid wasp Glyptapanteles flavicoxis

Females of the parasitoid wasp Glyptapanteles flavicoxis (Marsh) (Hymenoptera: Braconidae) deposit sex pheromone on substrate that elicits attraction and wing fanning in conspecific males. We tested the hypothesis that wing fanning sound induces a behavioral response from females which, in turn, affects the males’ orientation toward them. Females exposed to playback of the males’ wing fanning sound engaged in short flights, with sound characteristics different from those of the males’ wing fanning sound. In two‐choice bioassays, playback of the females’ flight sound attracted significantly more males than a silent control stimulus, and in combination with pheromone‐containing body extract of females it attracted more males than female body extract alone. Our data support the conclusion that the males’ wing fanning induces sound and visual reply signals from females that help males orient toward them.     

Sex-biased and body condition dependent dispersal capacity in the endangered saproxylic beetle <Emphasis Type="Italic">Osmoderma eremita</Emphasis> (Coleoptera: Cetoniidae)

The dispersal capacity of rare and endangered insect species has rarely been estimated even though it is essential for their management. For these species, laboratory based experiments are considered more appropriate for determining dispersal capacity as well as the factors influencing it. We aimed to characterize dispersal capacity of the endangered saproxylic beetle Osmoderma eremita (Scopoli, 1763) (Coleoptera: Cetoniidae). We studied the influence of sex and body condition on several parameters of dispersal (seven parameters of flight capacity measured in laboratory and pre-flight behaviour observed in the wild). Tethered flight experiments, conducted on 30 individuals collected in several regions of France, revealed: (1) maximal single flight distance of 1,454 m and maximal total flight distance of 2,361 m; (2) higher flight capacity in females than males; (3) flight speed and take-off completion decreasing with increasing body condition only for females. Additionally, 32 individuals displaying pre-flight behaviour in the wild showed similar interacting influences of sex and body condition: females initiating pre-flight behaviour had lower body condition than males. Thus, males and females have different dispersal strategies. We propose that body condition influences on dispersal capacity should be considered for species conservation by, for instance, managing adult food resources at the landscape scale and need to be taken into account in introduction programmes.     

Linking reproductive and feeding strategies in the parasitoid Ibalia leucospoides: does feeding always imply profit?

Resource acquisition and allocation to different biological functions over the course of life have strong implications for animal reproductive success. Animals can experience different environmental conditions during their lifetime, and this may play an important role in shaping their life-history and resource allocation strategies. In this study we investigate larval and adult resource allocation to reproductive and survival functions in the parasitoid wasp Ibalia leucospoides (family Ibaliidae). The pattern of larval resource allocation was inferred from the relationship between adult body size and ovigeny index (OI; a relative measure of investment in early reproduction determined as the ratio between the initial egg load and the potential lifetime fecundity); and adult resource allocation was explored through the influence of adult feeding on reproduction, maintenance and metabolism, in laboratory experiments. Food acquisition by this parasitoid in the wild was also examined. The relationship between size and OI was constant, suggesting no differential resource allocation to initial egg load and potential lifetime fecundity with size. This finding is in line with that predicted by adaptive models for the proovigenic egg maturation strategy (OI = 1). Despite of this, I. leucospoides showed a high OI of 0.77, which places this species among the weakly synovigenic ones (OI < 1). Adult feeding had no effect on post-emergence egg maturation. However, wasps extended their lifespan through feeding albeit only when food was provided ad libitum. Although the information we obtained on the feeding behaviour of free-foraging wasps is limited, our results suggest that food intake in the wild, while possible, may not be frequent in this parasitoid. We discuss the results relative to the environmental factors, such as reproductive opportunities and food availability, which may have driven the evolution of larval and adult pattern of resource allocation in parasitoids.     

Flight manoeuvers used by a parasitic wasp to locate host-infested plant

Cotesia rubecula Marshall (Hymenoptera: Braconidae) is a specialist larval parasitoid of the butterfly Pieris rapae L. which itself feeds almost exclusively upon cruciferous plants. Female wasps are attracted to the odour of host-infested plant (plant-host complex: PHC) and the probability of flights in a wind tunnel depends on females' prior oviposition experience with the PHC and on the concentration of the PHC odour. This study considers the effect of both factors on characteristics of oriented flight upwind towards the PHC. The flight track parameters that we measured and calculated were not significantly affected by these factors. C. rubecula females exhibited high average flight velocity and relatively straight flight tracks. There was a considerable variability between individuals, however, in their odour-modulated upwind flight tracks. Some females generated a zigzagging upwind flight track similar to those commonly observed from male moths responding to female sex pheromone. Other females flew along a straight track directly upwind. The flight tracks of most female wasps were intermediate between these extremes. The full range of these flight performances was observed to all experimental treatments.     

Egg resorption behaviour by the solitary egg parasitoid Anaphes nitens under natural conditions

We investigated under outdoor conditions and inside a climate chamber: (i) whether Anaphes nitens Girault (Hymenoptera: Mymaridae), an egg parasitoid of the Eucalyptus snout beetle, Gonipterus scutellatus Gyllenhal (Coleoptera: Curculionidae), experienced egg resorption, and (ii) how various treatments (location, food, and/or host supply) and body size influenced egg load, egg resorption, fecundity, and longevity. One‐day‐old females were mated and randomly assigned to five groups: (A) honey + hosts, (B) water + hosts, (C) only honey, (D) only water, and (E) control females killed at emergence. We compared the egg load of the newly emerged females, which represent the control group (egg load = ovarian eggs present at emergence), with the lifetime egg load (i.e., ovarian eggs + emerged offspring + not emerged offspring) of the females with various host and diet treatments, by dissection of the ovaries to find evidence of egg resorption. All groups reared outdoors had fewer eggs than the control, while indoors there was no significant difference. Outdoors, starved but host‐provided wasps (B) experienced the highest reduction of the lifetime egg load (51%). Groups without access to food (B + D) resorbed more eggs than groups provided with honey (A + C). Females with honey and hosts (A) had the highest lifetime fecundity, but those with water and hosts (B) showed a higher daily realized fecundity. Host‐deprived females with access to food (C) attained the longest lifespan. Our results suggest that under stress conditions, such as low temperature and food shortage, A. nitens females practice egg resorption, probably to save energy.     

Genetic variation in the behavioural mechanisms involved in the response of the egg parasitoid Trissolcus brochymenae to contact chemical cues left by the pest Murgantia histrionica

1. The ability of parasitoid females to perceive chemical traces left by their hosts is of utmost importance in the host location process. The behaviours involved in such ability have thus most likely been promoted by natural selection in the course of the evolutionary time. For this to happen, however, there must be significant genetic variation in natural populations on which natural selection could act.
2. Using the isofemale line method and motion analysis, we detected significant intra‐population genetic variation for several walking behaviour traits of the egg parasitoid Trissolcus brochymenae (Hymenoptera: Scelionidae) females responding to chemical traces left by its host Murgantia histrionica (Heteroptera: Pentatomidae).
3. Besides opening new avenues of research on the reproductive strategies, behaviour, and biological control potential of parasitoid wasps, these results also have implications for understanding their life‐history evolution in general.

     

The Effect of Abiotic Factors on the Male Mate Searching Behavior and the Mating Success of Aphidius ervi (Hymenoptera: Aphidiidae)

The effect of wind speed and distance from the source on the male response of the aphid parasitoid, Aphidius ervi (Hymenoptera: Aphidiidae), to a pheromone source was studied in a wind tunnel. The number of males taking flight, entering the plume and successfully reaching the source, decreased at wind speeds >50 cm/s. Furthermore, the proportion of those attempting upwind flight that fell to the ground increased with increasing wind speed. In contrast, distance from the source had no significant effect on any of the parameters examined. While male flight behavior was significantly reduced at 70 cm/s, some males walked to the source when there was a bridge connecting the pheromone source and the release platform. This suggests that ambulatory behavior could be a significant component of male mate searching in A. ervi when wind conditions are too strong for upwind flight. The possible effects of variation in atmospheric pressure on male flight behavior to the long distance pheromone, as well as to the short distance one, were also investigated. No significant effects of atmospheric pressure were observed. These findings differ significantly from those previously reported for another aphid parasitoid, A. nigripes, and the reasons for such differences are discussed.