Glyphosate-induced changes in the attack success and development of the mountain pine beetle and impact of its natural enemies

Roundup (active ingredient glyphosate) administered into the sapwood around the root collar of lodgepole pine trees, Pinus contorta var. latifolia Engelm., was investigated as a tool for creating trap trees for the mountain pine beetle (MPB), Dendroctonus ponderosae Hopk. MPB's attacked semiochemical-baited, glyphosate-treat trees before attacking baited control trees. Bark samples disclosed an increase in survival of MPB eggs and early instar larvae, enhanced larval development and increased attacks by insect parasites and predators in treated trees. The braconid wasp, Coeloides dendroctoni Cush., parasitized MPB larvae found at high densities in treated trees two months following attack. The dipteran predator, Medetera aldrichii Wh., was only found in treated trees. Increased competition by Ips pini (Say) had a negative impact on MPB survivorship. The enhanced impact of insectan agents apparently offset any glyphosate-induced gains in MPB survival or development, but did not cause a significant reduction in MPB emergence.     

Carbohydrate reserves,radial growth,and mechanisms of resistance of oak trees to phloem-boring insects

Summary The twolined chestnut borer, Agrilus bilineatus (Weber) (Coleoptera: Buprestidae), attacks oaks (Quercus spp.) that have been weakened by prior environmental or biotic stress. Our earlier work showed that trees with relatively low winter starch reserves are more likely to be attacked by A. bilineatus the following summer. We hypothesized that such trees may have less energy available for defense (Callus formation and allelo-chemical synthesis) in tissues wounded by borer larvae. However, wounding experiments showed little or no relationship between winter or summer carbohydrate reserves, callus formation, radial growth, or concentrations of tannins and phenolics in wounded or nonwounded phloem tissues. Trees with relatively low winter carbohydrate reserves were again found to be attractive to adult A. bilineatus, although not all low starch trees were attacked or successfully colonized by borers. There was a trend for carpenterworm larvae, Prinoxystus robiniae (Lepidoptera: Cossidae), a generalist bark and wood borer, to be more successful in establishing galleries on low starch trees. Carpenterworms gained significantly more weight when fed phloem from trees attractive to A. bilineatus. Oaks that attracted large numbers of A. bilineatus or that were successfully colonized by the borer produced significantly less callus than did non-attacked trees when experimentally wounded at about the time of Agrilus egg hatch. Callus formation may limit the establishment of small larvae that feed slowly in the cambial region. These results indicate that current theory regarding relationships between increased tree stress and decreased allocation of energy reserves to radial growth and defense against phloem borers may be an oversimplification. We suggest that tree growth and the defensive response of phloem tissues may be limited more by the rate of carbohydrate utilization or by changes in source-sink relationships than by storage levels. Callus formation and synthesis of allelochemicals in wounded phloem may be under the same control as cambial activation, which is mediated by plant growth regulators and can be influenced by environmental conditions.     

Interactions between ants attendingAphis fabae ssp.cirsiiacanthoidis on thistles and foraging parasitoid wasps

We describe the behavioral interactions between honeydew-collecting workers of the ants Lasius nigerand Myrmica ruginodisand females of three species of aphidiid wasps (Lysiphlebus cardui, Lysiphlebus testaceipes, Trioxys angelicae)foraging for their aphid host, Aphis fabaessp. cirsiiacanthoidis,on thistles. Using field and laboratory experiments, we show that the ant-parasitoid interactions are species specific. Workers of both ant species generally attacked and killed females of T. angelicae,but they ignored those of L. cardui.This pattern was not altered when we anesthetized the wasps slightly with carbon dioxide to reduce their mobility. Prior contacts between L. carduiand either conspecific L. nigerfrom a different nest or workers of a different ant species (M. ruginodis)did not influence L. niger'snonaggressive behavior. The number of aphids parasitized by L. testaceipeswas significantly reduced in aphid colonies attended by L. niger,although this parasitoid was rarely attacked by ants. In encounters between these species of ants and wasps, ant aggression is consistent with differences in wasp behavior. We suggest that, in addition, chemical cues located in the cuticula may enable L. carduito avoid detection by honeydew-collecting ants.     

Parasitism of orangestriped oakworm (Lepidoptera: Saturniidae) eggs in the urban landscape

Orangestriped oakworm, Anisota senatoria (J. E. Smith), has caused widespread defoliation of oak trees in the urban landscape of southeastern Virginia since 1985. Egg masses were collected from 1988 to 1990 to determine the impact of native egg parasites on A. senatoria populations. The most abundant egg parasite was Aprostocetus new sp. and mean egg mass parasitism was 24.6%. The eupelmid Anastatus hirtus (Ashmead), a new host record, parasitized a mean of 11.7% of A. senatoria egg masses. The encyrtid Ooencytrus sp., a new host record, had a mean egg mass parasitism of 0.09%. Inundative releases of Trichogramma minutum (Riley) in 1989 and 1990 did not increase parasitism rates and mean egg mass parasitism was 2.3%. Parasitism of first generation A. senatoria egg masses was higher compared with second generation. The four egg parasites collected in this study parasitized 30% of A. senatoria egg masses and within egg mass parasitism was 7.9%. These relatively low parasitism rates may partially explain the presence of consistently high A. senatoria populations in southeastern Virginia.     

Consequences of chronic infections with three different avian malaria lineages on reproductive performance of Lesser Kestrels (Falco naumanni)

We studied the consequences of chronic infections by three different lineages of avian malaria, two Plasmodium (RTSR1, LK6) and one Haemoproteus (LK2), on reproductive performance of Lesser Kestrels (Falco naumanni). Malaria infections in male and female parents had no effect on clutch size, hatching success or nesting success. However, when only successful nests were considered, we found that males parasitized by LK6 raised a lower number of fledglings, suggesting that the level of parental effort by males may be limited by this particular lineage of Plasmodium. This effect was not evident in females, probably due to the higher investment of males during the chick rearing period in this species. Overall, we have found that chronic stages of specific malaria lineages have certain negative consequences on host reproductive performance, highlighting the importance of considering genetic differences among malaria parasites to study their consequences on natural bird populations.     

Variation in life-history traits among Urtica dioica populations with different history in parasitism by the holoparasitic plant Cuscuta europaea

Several studies demonstrate that natural enemies (e.g. parasites) have profound negative effects on the life-history traits of their hosts. If the host can compensate for the negative effects of parasitic infection by altering its life history, these modifications may partly form the basis of resistance or tolerance against parasites. Thus, parasites may be of considerable importance in shaping the evolution of life-history traits of their hosts. To examine if previous parasitism is associated with differences in life-history traits of the host, I conducted a common garden experiment with Urtica dioica plants originating from eight populations of which four were unparasitized, and four parasitized by the holoparasitic plant, Cuscuta europaea. A field survey indicated no differences between unparasitized and parasitized populations in, for example, the number of plant species and nutrient levels in the soil. Thus, it seems reasonable to assume that differences in life-history traits between the two population types in the common garden would reflect the effects of previous selection by the parasite. In the common garden, plants from parasitized populations started to flower later and allocated less biomass to asexual reproduction (measured as the production of stolons, i.e. clonal propagation) compared to plants from unparasitized populations. These results thus indicate that selection by the parasite may have favoured later onset of flowering, and may have selected against asexual reproduction.     

Recognition of heterospecific parasitism: Competition between Aphidiid (Aphidius ervi) and Aphelinid (Aphelinus asychis) parasitoids of Aphids (Hymenoptera: Aphidiidae; Aphelinidae)

The solitary parasitoids Aphidius erviHaliday (Hymenoptera: Aphidiidae) and Aphelinus asychisWalker (Hymenoptera: Aphelinidae) attacked but generally did not oviposit in pea aphids parasitized by the other species. Wasps selectively oviposited in unparasitized hosts when given a choice. Host discrimination depended on the recognition of internal cues. Females of A. asychiseither could not recognize or ignored A. ervi'sexternal host marking pheromone. Under most conditions, A. ervisurvived in superparasitized hosts, killing competing A. asychislarvae by physical attack and possibly physiological suppression. The outcome of larval competition was not affected by oviposition sequence or age difference between larvae; A. asychissurvived only when it had substantially completed larval development before the host was superparasitized by A. ervi.It is suggested that competition for host resources incurs a cost, for the winner in terms of reduced size or increased development time and for the loser in terms of lost progeny and searching time. Consequently, heterospecific host discrimination can be functional. Internal, and probably general, cues enable wasps to recognize and avoid oviposition in hosts already parasitized by an unrelated species.     

Interspecific competition between the braconid endoparasitoids Glyptapanteles porthetriae and Glyptapanteles liparidis in Lymantria dispar larvae

The effect of interspecific competition between the solitary endoparasitoid Glyptapanteles porthetriae Muesebeck (Hymenoptera: Braconidae) and the gregarious Glyptapanteles liparidis Bouché (Hymenoptera: Braconidae), was investigated in larvae of Lymantria dispar L. (Lepidoptera: Lymantriidae). Host larvae were parasitized by both wasp species simultaneously in premolt to the 2^nd or the 3^rd host instar or in an additional approach with a 4-day delay in parasitization by the second wasp species. Host acceptance experiments revealed that both wasp species do not discriminate between unparasitized host larvae and larvae parasitized previously by the same or the other species. In more than 90% female wasps parasitized the larva they encountered first. During the period of endoparasitic development, larvae of the competing parasitoid species never attacked the egg stage of the other species. When host larvae were parasitized simultaneously by both wasp species, the rate of successful development of both species depended on the age of the host larva at the time of its parasitization; G. liparidis emerged successfully from 44% of host larvae parasitized during the premolt to 2^nd instar, G. porthetriae from 28%, and in 20% of the hosts both parasitoid species were able to develop in one gypsy moth larva. However, when host larvae were parasitized simultaneously during premolt to the 3^rd instar, G. liparidis was successful in 90% of the hosts, compared to 8% from which only G. porthetriae emerged. In the experiments with delayed oviposition, generally the species that oviposited first succeeded in completing its larval development. Larvae of the species ovipositing with four days delay were frequently attacked and killed by larvae of the first parasitizing species or suffered reduced growth. As the secondary parasitoid species, G. porthetriae-larvae were never able to complete their development, whereas G. liparidis developed successfully in at least 12,5% of the multiparasitized host larvae. Thus, multiparasitism of gypsy moth larvae by both Glyptapanteles species corresponds to the contest type; however, G. porthetriae is only able to develop successfully as the primary parasitoid of young host larvae.     

Effect of distance,aggregation, and habitat on levels of seed predation for two mammal — dispersed neotropical rain forest tree species

The effect of seed aggregation and distance from conspecific trees on seed predation was experimentally examined for two neotropical tree species, Macoubea guianensis (Apocynaceae) and Pouteria sp. (Sapotaceae) in a lowland tropical rain forest in northeastern Peru. Results of these experiments are discussed in the context of the Janzen-Connell model (Janzen 1970; Connell 1971), which predicts decreased seed survival near parent trees due to either density-or distance-responsive mortality, and Howe's model (Howe 1989) which predicts that trees with seeds dispersed in clumps (aggregated) will not suffer density-dependent predation, and will have higher survival of seeds near the parent tree than other trees. We also examined whether predation on seeds of these species was affected by seed placement in or near 30-m-wide strips regenerating after clear-cutting. Both species appeared to be mammal-dispersed but differed in how frugivores handled seeds, seed size, overall fruit crop size, and gemination time. Neither of the two species studied appeared to suffer seed predation in a manner predicted by the Janzen-Connell model, and patterns of seed predation for only one of the species was similar to predictions of Howe's model. For neither species did seed predation along the edge of, or in the center of, regenerating clear cuts differ from predation 15 m into the primary forest. For Pouteria, seed predation in and near regnerating strips was significantly greater than around forest trees, but the opposite pattern held for Macoubea. Overall, seed predation was much greater on Macoubea. The difference in seed predation for these two species was most likely a result of differences in the types of seed predators that attacked these two species.     

Host-discrimination by <Emphasis Type="Italic">Phymastichus coffea</Emphasis>, a parasitoid of the coffee berry borer

Phymastichus coffea (LaSalle) (Hymenoptera: Eulophidae) is an African endoparasitoid of the coffee berry borer, Hypothenemus hampei (Ferrari) (Coleoptera: Scolytidae) that has been introduced to several countries to control this important pest. In the present study we performed a series of laboratory experiments in order to determine if there was evidence of host discrimination and superparasitism in P. coffea. Our choice experiments demonstrate that P. coffea females showed significant preference to attack unparasitized hosts, rather than those parasitized conspecifically. No significant preferences were detected in self-specific attacks between parasitized hosts and the healthy ones. A further dissection of hosts sequentially attacked either self or conspecifically, revealed that there were no more than two eggs per host. As P. coffea is a species that normally allocates two eggs per host in a single attack, we assumed that females were able to attack already parasitized hosts, but they did not lay eggs in them. Based on this fact, we conclude that there is a host discrimination ability in P. coffea females. With respect to the superparasitism by P. coffea using non-choice experiments, there was no significant difference between self-specific or conspecific attacks with respect to the control after one or two successive attacks. Conspecific attacks yielded the largest numbers of eggs after 3rd, 4th and 5th attacks and significant differences were found between this treatment and the control. The maximum number of eggs found in a single host was six individuals (conspecific treatment). These results confirmed that P. coffea usually laid two eggs per host; however, when there are no hosts available, conspecific attacks can result in the superparasitism in this species.     

The influence of host fruit morphology on parasitization rates in the Caribbean fruit fly,Anastrepha suspensa

Among the host fruits of the Caribbean fruit fly there are a variety of sizes and shapes. These morphological differences may influence the vulnerability of the larvae to parasites. In the laboratory, Caribbean fruit fly larvae placed in the smaller of 2 different sizes of artificial ‘fruit’ (cloth spheres filled with a diet material) were parasitized at a higher rate by the braconid,Diachasmimorpha longicaudata (Ashmead) when spheres were presented separately. However, when parasites were simultaneously presented with 6 different sizes of ‘fruit’ there was no significant relationship between size and parasitization rate. This may be due to the parasites preference to search for larvae in larger ‘fruit’. In field collections of different species of host fruit, a significant inverse correlation exists between fruit radius and rate of parasitization. However, host fruit size accounts for only about 5% of the variance in yearly parasitization rates.      

Host selection and larval interactions among three primary parasitoids ofPlathypena scabra (Lep.: noctuidae)

Three hymenopteran parasitoids that attackPlathypena scabra (F.) larvae often oviposit into consecutive instars of the host. We investigated host discrimination by adults and competitive interactions among larvae of these three parasitoid species. Avoidance of superparasitism byCotesia marginiventris (Cresson) andDiolcogaster facetosa Ashmead was tested. Females of each species were presented either withP. scabra parasitized by a different female of the same species 6 h earlier or unparasitizedP. scabra. Under these conditions,C. marginiventris attacked similar numbers of parasitized and unparasitized hosts.D. facetosa attacked 31% fewer parasitized than unparasitizedP. scabra. The avoidance of multiple parasitism byD. facetosa was studied in a similar bioassay. AlthoughD. facetosa females parasitized fewerP. scabra that had been attacked byC. marginiventris 6 h previously, the reduction in parasitism was only about 23%. In competition studies, immatureD. facetosa were better competitors than immatureC. marginiventris. Aleiodes (=Rogas) nolophanae (Ashmead) was an inferior competitor against bothC. marginiventris andD. facetosa when the duration between parasitism events was 1 h, but their competitive ability increased when they multiply parasitized hosts at least 32 h after the initial oviposition.     

Predator and parasitoid attacking ant-attended aphids: effects of predator presence and attending ant species on emerging parasitoid numbers

Interaction between a predator and a parasitoid attacking ant-attended aphids was examined in a system on photinia plants, consisting of the aphid Aphis spiraecola, the two ants Lasius japonicus and Pristomyrmex pungens, the predatory ladybird beetle Scymnus posticalis, and the parasitoid wasp Lysiphlebus japonicus. The ladybird larvae are densely covered with waxy secretion and are never attacked by attending ants. The parasitoid females are often attacked by ants, but successfully oviposit by avoiding ants. The two ants differ in aggressiveness towards aphid enemies. Impacts of the predator larvae and attending ant species on the number of parasitoid adults emerging from mummies per aphid colony were assessed by manipulating the presence of the predator in introduced aphid colonies attended by either ant. The experiment showed a significant negative impact of the predator on emerging parasitoid numbers. This is due to consumption of healthy aphids by the predator and its predation on parasitized aphids containing the parasitoid larvae (intraguild predation). Additionally, attending ant species significantly affected emerging parasitoid numbers, with more parasitoids in P. pungens-attended colonies. This results from the lower extent of interference with parasitoid oviposition by the less aggressive P. pungens. Furthermore, the predator reduced emerging parasitoid numbers more when P. pungens attended aphids. This may be ascribed to larger numbers of the predator and the resulting higher levels of predation on unparasitized and parasitized aphids in P. pungens-attended colonies. In conclusion, a negative effect of the predator on the parasitoid occurs in ant-attended aphid colonies, and the intensity of the interaction is affected by ant species.     

Parasites of the spotted stalk borer,Chilo partellus [Lepidoptera: Pyralidae] in South Africa

One egg parasite, 7 larval parasites, 2 pupal parasites and 3 larval hyperparasites were recorded parasitizing the spotted stalk borer,Chilo partellus (Swinhoe) on maize and grain sorghum in South Africa.Trichogrammatoidea lutea Girault [Trichogrammatidae] parasitized eggs ofC. partellus mainly in mid-summer. The larval parasites were active throughout the season with occasional peaks of up to 75% parasitism.Apanteles sesamiae Cameron [Braconidae], proved to be the most abundant larval parasite. It was recorded fromca. 93% of parasitized larvae but its efficiency was reduced by the hyperparasite,Aphanogmus fijiensis (Ferriére) [Ceraphronidae], which reached sometimes up to 100% parasitism on cocoons ofA. sesamiae. The efficiency ofIphiaulax sp. [Braconidae], the 2^nd most abundant larval parasite, was also hindered by the hyperparasite,Eurytoma sp. [Eurytomidae] Pupal parasites were sometimes very abundant reaching up to 100% parasitism without any interference by hyperparasites. The most abundant pupal parasites wereDentichasmias busseolae Heinrich [Ichneumonidae] andPediobius furvus (Gahan) [Eulophidae].      

Emission of volatile organic compounds by apple trees under spider mite attack and attraction of predatory mites

Emission rates of volatile organic compounds (VOCs) from Pirus malus L. subsp. mitis (Wallr.) var. Golden Delicious and var. Starking attacked by the phytophagous mite Panonychus ulmi Koch, and their attractiveness to the predatory mites Amblyseius andersoni Chant and Amblyseius californicus McGregor, were studied during three years. A large variability was found in the emission of individual VOCs depending on the infestation, the apple tree variety and the date. There were larger total VOC emission rates and larger total VOC leaf concentrations in apple trees attacked by phytophagous mites, especially in the var. Starking. In infested trees of this variety, there were also more predatory mites. An olfactometer assay showed that predatory mites preferentially chose branches infested by Panonychus ulmi (85% went to infested branches vs 15% to uninfested control branches) indicating that volatiles may be used as cues to find their prey.     

Parasitoid complex of black scale <Emphasis Type="Italic">Saissetia oleae</Emphasis> on citrus and olives: parasitoid species composition and seasonal trend

The parasitoid complex of black scale Saissetia oleae (Olivier) (Hemiptera: Coccidae) was studied on citrus and olives to determine their relative abundance, seasonal trend, geographical distribution, and their incidence on black scale populations. Branches and leaves of ten citrus and four olive groves infested with black scale were periodically collected over the period March 2003–December 2005 in eastern Spain, covering an area of 10,000 km². Adult parasitoids were also sampled with a portable engine-powered suction device. Black scale females were attacked by Scutellista caerulea (Fonscolombe) (Hymenoptera: Pteromalidae), which was found beneath 35.4 ± 7.5% and 22.4 ± 3.5% female scale’s body in citrus and olive groves, respectively. However, S. caerulea attacked the scales when most of their eggs had already hatched. The parasitic mite Pyemotes herfsi (Oudemans) (Prostigmata: Pyemotidae) fed on all development stages of S. caerulea. The gregarious female’s endoparasitoid Metaphycus lounsburyi (Howard) (Hymenoptera: Encyrtidae) was common in citrus and olive trees, but the parasitism rates it reached was low. Second and third instars of black scale were mainly parasitized by the solitary endoparasitoid Metaphycus flavus (Howard), and secondarily by Metaphycus helvolus (Compere) which was much less abundant and limited in distribution. Thus, M. helvolus, introduced 30 years ago, has not displaced M. flavus as in other Mediterranean areas. According to their abundance, distribution and incidence, M. flavus and S. caerulea appeared as the main parasitoids of black scale in eastern Spain, whereas M. helvolus and M. lounsburyi, considered the main parasitoids in other citrus and olive areas of the world, had a limited incidence. Recommendations for improving the level of biological control are discussed.     

Laboratory rearing ofAnaphes sordidatus [Hym.: Mymaridae] on carrot weevil eggs [Col.: Curculionidae]

A technique for rearingAnaphes sordidatus (Girault) on eggs of laboratory-reared carrot weevil,Listronotus oregonensis (Le Conte), is described. Individual rearing was possible by using polyethylene embedding capsules that enabled easy manipulation of parasitized carrot weevil eggs for use in subsequent experimental procedures. The technique described resulted in 65% parasitization of carrot weevil eggs and 90 mn per day were sufficient to obtainca. 200 parasites daily.      

Host selection by the heteronomous hyperparasitoid Encarsia pergandiella: multiple-choice tests using Bemisia argentifolii as primary host

The ovipositional patterns of the heteronomous hyperparasitoid Encarsia pergandiella Howard (Hymenoptera: Aphelinidae) in the presence of its primary host Bemisia argentifolii Bellows & Perring (Hemiptera: Aleyrodidae), and in the presence or absence of conspecific and heterospecific secondary hosts (Encarsia formosa Gahan andEretmocerus mundus Mercet; Hymenoptera: Aphelinidae) were examined to assess host species preferences. Host preferences by heteronomous hyperparasitoids may affect the relative abundance of co-occurring parasitoid species and may influence host population suppression by the parasitoid community. Four combinations of hosts were tested: (1) B. argentifolii, E. mundus, and E. formosa, (2) B. argentifolii, E. formosa, and E. pergandiella, (3) B. argentifolii, E. mundus, and E. pergandiella, and, (4) B. argentifolii, E. mundus, E. formosa, and E. pergandiella. Arrays of hosts (24) were constructed in Petri dishes using leaf disks, each bearing one host. Thirty arrays of each host combination were exposed to single females for 6 h. All hosts were dissected to determine number of eggs per host. Encarsia pergandiella parasitized E. formosa hosts as frequently as E. mundus hosts. However, E. pergandiella parasitized either of these heterospecific hosts more frequently than conspecific hosts in treatments including two secondary host species. When a third parasitoid species was included in host arrays, E. pergandiella parasitized conspecific hosts as frequently as heterospecific hosts. Developmental stage of the hosts did not significantly influence host species selection by E. pergandiella. Our results indicate that host selection and oviposition by heteronomous hyperparasitoids like E. pergandiella, vary with the composition of hosts available for parasitization, and suggest a preference for heterospecific over conspecific secondary hosts.     

Changes in abundance of native and introduced parasites (Hymenoptera: Braconidae), and of the target and non-target plant bug species (Hemiptera: Miridae), during two classical biological control programs in alfalfa.

High numbers of tarnished plant bugs [Lygus lineolaris (Palisot)], were once common in alfalfa, as was a low level of parasitism (9%) by the native Peristenus pallipes (Curtis). After the bivoltine European parasite Peristenus digoneutis Loan became well established, average parasitism of the first and second generations increased to 64%, and tarnished plant bug numbers dropped by 65%. This reduced host density eventually caused a decline in total parasitism by both parasite species to 22%. A few P. digoneutis also attacked the alfalfa plant bug, Adelphocoris lineolatus (Goeze), but did not reduce this pest or increase its parasitism rate. At another location, where P. digoneutis is not established, parasitism of first generation alfalfa plant bugs, an adventive (accidently introduced) pest, was increased to 21% by the introduced univoltine parasite, Peristenus conradi Marsh, and a slight reduction in the pest may have resulted. P. digoneutis did not parasitize the meadow plant bug, Leptopterna dolabrata (L.), an adventive pest of forage grasses, so did not affect this mirid or its parasite. Neither introduced parasite eliminated the native parasites of the tarnished or alfalfa plant bugs. The narrow host ranges of the braconid parasites of mirid nymphs are contrasted with the broad host range of the native tachinid parasite [Phasia robertsoni (Towns.)] of adult mirids. The major changes in mirid abundance and their mortality by parasites that slowly occurred during this 19-year study demonstrate the need for long-term field research, to adequately document and understand these complex interactions.