Unparasitized Aphids Research Articles

Geographic and microgeographic genetic differentiation in two aphid species over southern England using the multilocus (GATA)4 probe.

Samples of the grain aphid Sitobion avenae (F.) and the rose-grain aphid Metopolophium dirhodum (Walker) were collected in late March from wheat fields and adjacent road-side grasses at a number of locations in southern England. Unparasitized aphids were DNA fingerprinted using the multilocus (GATA)4 probe. Over all locations, the fingerprints of individual S. avenae caught in wheat had lower overall average distances of band migration (ADBM) and shared a higher proportion of bands, than fingerprints of individuals caught in adjacent road-side grasses. The ADBM of fingerprints of S. avenae collected on road-side grasses altered significantly with geographical location, while the ADBM of fingerprints of S. avenae caught on wheat did not. A comparison of the fingerprints of individual M. dirhodum caught in wheat and neighbouring road-side grasses did not reveal any genetic differentiation. Fingerprints of M. dirhodum that were caught in the same host type did however, show significant variation in ADBM between different locations. With both S. avenae and M. dirhodum, spatial autocorrelation revealed that locations that were close together were no more likely to have individuals with similar ADBM than locations that were far apart. Our results suggest that (i) particular clones of S. avenae prefer to colonize wheat, and/or that (ii) particular clones of S. avenae perform better on wheat than other clones. It is unclear why M. dirhodum did not show any genetic structuring according to host type, but this species appears to engage in sexual reproduction much more frequently than S. avenae in southern England.(ABSTRACT TRUNCATED AT 250 WORDS)

Oviposition Behavior of Monoctonus paulensis (Hymenoptera: Aphidiidae): Factors Influencing Reproductive Allocation to Hosts and Host Patches

Mated females of the solitary parasitoid Monoctonus paulensis (Ashmead) frequently self-superparasitize pea aphids, Acyrthosiphon pisum (Harris), during single encounters. Superparasitism varied with egg load but was independent of host density. Two-day-old virgin females abandoned host patches earlier, and superparasitized fewer pea aphids, than did 2-d-old mated females. Six-day-old virgins did not superparasitize more pea aphids than did 2-d-old virgins. However, 6-d-old virgins remained in host patches as long as mated females of the same age, and ai tacked similar numbers of aphids. Prepatch encounters with conspecific females caused virgins to superparasitize a larger proportion of aphids. Virgin females that had encountered con specifically parasitized aphids shortly after emergence remained longer in patches of unparasitized aphids, and parasitized a larger proportion of them, than did virgins that had encountered only unparasitized aphids.

Morphological observations on the preimaginal stages ofAphelinus varipes (Hym., Aphelinidae) and the effects of this parasitoid on the aphidRhopalosiphum padi (Hom., Aphididae)

Three instar larvae could be observed forAphelinus varipes. In the second and third instars, the colon which forms the largest part of the hindgut was composed of secretory cells. There was a reduction in the size and number of embryos produced by parasitized aphids. Fat cells of parasitized aphids also degenerated sooner than those of unparasitized aphids. The number of mycetocytes remained higher in parasitizedRhopalosiphum padi than in non-parasitized aphids. During the last instar ofA. varipes the host aphid developed into a mummy in which black pigments were incorporated into the exocuticle and the integument of the aphid became sclerotized.

Nutritional Ecology of an Insect Host‐Parasitoid Association: The Pea Aphid‐Aphidius Ervi System

Evolutionary host—size models assume that host quality for parasitoid growth and development is a linear function of host size. To test this assumption, we compared the growth patterns of the hymenopteran parasitoid Aphidius ervi when it developed in different nymphal instars of apterous pea aphids, Acyrthosiphon pisum. At daily intervals, unparasitized aphids and aphids that were parasitized at age 24, 48, 72, and 120 h (corresponding to nymphal instars L1—L4) were dissected. We weighed parasitoid larvae and host remains to determine changes in their relative growth rates, based on wet mass (WM) and dry mass (DM). The growth in DM of unparasitized aphids followed a sigmoid curve. Aphids that were parasitized by A. ervi continued to grow for 5—7 d before their DM started to decline. Trajectories of the parasitoid's growth during its larval and pupal stages could be described by nonlinear equations. The maximum larval DM and the time for oviposition to adult eclosion of parasitoids varied with host age at parasitization, and thus suggested differences in host quality. We proposed that, for parasitoids developing in growing and feeding stages of the host, host quality is not a linear function of host size at parasitization but reflects the degree of integration of the two systems.

Influence of Superparasitism on Development Rate and Adult Size in a Solitary Parasitoid Wasp, Aphidius ervi

We tested the assumption that superparasitism by solitary species of parasitoid wasps has no fitness consequences For the surviving larva. Using Aphidius ervi and its aphid host, Acyrthosiphon pisum, as an experimental system, we compared adult dry mass and development time from oviposition to adult eclosion between male wasps that developed in single- and in superparasitized aphids. Parasitoids gained 14% more dry mass (with no increase in development time) in superparasitized hosts. It is suggested that superparasitized aphids have higher growth potential for the surviving parasitoid larva because they ingest more food than single-parasitized and unparasitized aphids, in that order

AGE-SPECIFIC PATTERN OF HOST DISCRIMINATION BY THE APHID PARASITOID EPHEDRUS CALIFORNICUS BAKER (HYMENOPTERA: APHIDIIDAE)

AbstractThe solitary aphid parasitoid Ephedrus californicus Baker is able to discriminate between unparasitized and parasitized third-instar nymphs of the pea aphid, Acyrthosiphon pisum (Harris). Superparasitism varied with the number of mature eggs (which is age-dependent) present in the ovaries as well as with the number and the quality of any hosts encountered. Conspecific superparasitism varied with wasp age; older females, with a large egg supply, accepted hosts parasitized by a conspecific female if unparasitized aphids were unavailable. Self superparasitism occurred at all ages; it was the least likely behaviour compared with egg deposition in unparasitized and conspecific-parasitized hosts. Prior experience (learning) was not necessary for host discrimination, but it did influence the search rate, which was higher in inexperienced than experienced females. In choice experiments, wasps preferred conspecific- over self-parasitized aphids and thus were able to distinguish between them. It is suggested that oviposition markers vary among conspecific females. The data are discussed with reference to theories about oviposition decisions and progeny allocation in solitary hymenopteran parasitoids.

HOST DISCRIMINATION BY THE APHID PARASITOID APHELINUS ASYCHIS (HYMENOPTERA: APHELINIDAE): WHEN SUPERPARASITISM IS NOT ADAPTIVE

AbstractFemales of the solitary parasitoid Aphelinus asychis Walker discriminated between unparasitized and parasitized second-instar nymphs of the pea aphid, Acyrthosiphon pisum (Harris). Wasps normally avoided superparasitism, except when they were confined with few hosts for a long time. Parasitoid females did not need previous experience with unparasitized aphids (learning) in order to discriminate. They probed with the ovipositor any aphids encountered, a behaviour suggesting that host acceptance and rejection were determined by internal cues. Prolonged ovipositor insertion (>80 s) was correlated with host acceptance and egg deposition, but short insertion times (≤80 s) generally indicated host rejection. Females tended to reject both self- and conspecific-parasitized aphids when provided with two of each kind. We consider hypotheses mat conspecific superparasitism may be adaptive and give examples to show exceptions. We propose that, in egg-limited parasitoid species such as A. asychis, a reproductive strategy based on the regulation of egg production and on oosorption can explain the equal avoidance of self and conspecific superparasitism.

Oviposition and host‐feeding patterns in Aphelinus asychis (Hymenoptera: Aphelinidae) at different aphid densities

Abstract. 1. The patterns of host‐feeding and oviposition were examined in Aphelinus asychis Walker, which had been provided with second‐instar pea aphids as hosts.2. Female wasps responded to increasing host density (between one and forty aphids for 24 h) with an increasing tendency to oviposit rather than to feed. Superparasitism occurred at all aphid densities, even when unparasitized aphids were available.3. Aphids intended for feeding were paralysed and died. Wasps did not feed on and oviposit in the same aphid.4. Feeding to satiation lasted between 4 min and 42 min. Females that had starved for ≰18 h generally deposited one or more eggs before feeding again, while the reverse was true in wasps that had starved for 21 h.5. The host‐feeding behaviour of A. asychis is determined by a female's nutritional status. At low rates of host encounter, the anhydropic eggs may be resorbed. This reproductive strategy conforms to the destructive non‐concurrent type among the Hymenoptera.

APHID FECUNDITY, REPRODUCTIVE LONGEVITY, AND PARASITE DEVELOPMENT IN THE SCHIZAPHIS GRAMINUM (RONDANI)(HOMOPTERA: APHIDIDAE) – LYSIPHLEBUS TESTACEIPES (CRESSON) (HYMENOPTERA: BRACONIDAE) SYSTEM

AbstractThe fecundity and reproductive longevity of Schizaphis graminum (Rondani) parasitized by Lysiphlebus testaceipes (Cresson) were determined in the laboratory under four temperature regimes. Daily reproduction by S. graminum declined rapidly after parasitization except at a relatively low temperature regime (12–16 °C). The mean progeny production by parasitized aphids of 2.75 ± 0.08 nymphs per parasitized adult was not significantly different than that for unparasitized aphids (2.94 ± 0.23 nymphs) during the period of time equal to the reproductive life of parasitized aphids. Reproductive longevity of parasitized aphids was longest at the lowest temperature (5.67 ± 0.25 days at 12–16 °C). No significant differences were observed in total progeny produced at different temperatures. The number of progeny within parasitized nulliparous adults (3.37 ± 0.33) as determined by dissections was not significantly different from the mean total progeny produced by parasitized aphids. Parasitization thus seems to interfere with oogenesis, but not with embryonic development or progeny deposition.

Parasitism byEphedrus cerasicola [Hym.: Aphidiidae] developing in different stages ofMyzus persicae [Hom.: Aphididae

The parasitoidEphedrus cerasicola Stary oviposited in the 4 nymphal instars and in newly moulted apterous adults ofMyzus persicae (Sulzer). Development and reproduction of unparasitized and parasitized aphids at 21°C were compared. Unparasitized aphids developed to adults in 6.5 days and started to reproduce after 7 days. Longevity varied between 7 and 42 days. Net reproductive rate (R0) was 40.7. In contrast to older nymphs, aphids parasitized in the 1 st instar almost never reached the adult stage before mummification. Aphids parasitized in 2nd, 3rd and 4th instar and as newly moulted adults produced respectively 0.07 %, 2 %, 23 % and 32 % of offspring produced by unparasitized aphids. Corresponding reproductive periods were 1, 1.4, 3 and 4 days. Host age at parasitization had a slight effect on the parasitoid's developmental rate and had no effect on egg or pupal survival, or on the sex ratio of the emerging parasitoids.

REPRODUCTION AND LONGEVITY OF CABBAGE APHID,BREVICORYNE BRASSICAE(HOMOPTERA: APHIDIDAE), PARASITIZED BYDIAERETIELLA RAPAE(HYMENOPTERA: APHIDIIDAE)

AbstractParasitized cabbage aphids,Brevicoryne brassicae(Linnaeus), produced fewer offspring than unparasitized aphids. Aphids parasitized byDiaeretiella rapae(M'Intosh) during the first, second, or third instar died before producing any offspring; those parasitized during the fourth instar or the adult stage produced a variable number of offspring. The aphid's survival time was correlated with the rate of development, as measured by the length of the pre-reproductive period. A multiple-linear-regression equation is provided for predicting the mean total fecundity of parasitized cabbage aphids from the host age at the beginning of parasitism and the pre-reproductive period.

Limitation of superparasitism by Aphidius rhopalosiphi: a consequence of aphid defensive behaviour

Abstract. 1. The behavioural mechanisms limiting superparasitism by Aphidius rhopalosiphi (DeStefani‐Perez) are described.2. A.rhopalosiphi did not discriminate between parasitized and unparasitized aphids, or avoid attacking and ovipositing in previously parasitized aphids.3. Aphid defensive behaviour was increased for a short period after a parasite stabbing attack. In response to this behaviour the number of parasite stabbing attacks subsequently undertaken declined.4. Once a stabbing attack had been initiated, parasite oviposition success was unaffected by aphid defensive behaviour.5. It is concluded that applied defensive behaviour, by limiting the number of stabbing attacks undertaken by A.rhopalusiphi, effectively limits the number of parasite eggs laid and the extent to which super parasitism occurs.

Preference for and Effect of Greenbug 1 Parasitism and Feeding by Aphelinus asychis 23

The ages of greenbugs, Schizaphis graminum (Rondani), preferred for oviposition and feeding by the parasite Aphelinus asychis (Walker), the percent parasite emergence, aphid age class, and the reproductivity of stung and parasitized aphids were determined under laboratory conditions. Statistical analyses of data were made to study the daily reproductive potential of A. asychis . The parasite's preference was young>middle>old for oviposition and young>old>middle aged aphids for feeding. Elapsed time from oviposition to emergence of parasites was usually 11–12 days for all age groups of aphids with males usually the 1st to emerge. Success in parasite oviposition generally decreased as the age of the aphid increased. No aphid progeny was produced if they were parasitized during the 1st 3 days of their lives. Aphids which were parasitized when they became older showed a significant decrease in reproduction. Stung unparasitized aphids reproduced at a rate similar to unstung aphids.

Studies on Host Selection and Host Specificity of the Aphid Hyperparasite Charips victrix (Hymenoptera: Cynipidae). 5. Host Selection

Several aspects of host selection by Charips victrix (Westwood) were investigated. The following summarizes the experimental findings: (1) unparasitized aphids were probed but eggs were not deposited in them; (2) parasitized aphids were found readily among unparasitized aphids; (3) unparasitized pea aphids, Acyrthosiphon pisum (Harris), were probed more frequently by females than unparasitized spotted alfalfa aphids, Therioaphis trifolii (Monell); (4) more eggs were deposited in larvae of Aphidius smithi Sharma & Subba Rao through the pea aphid than in larvae of Trioxys complanatus Quilis through the spotted alfalfa aphid; and (5) C. victrix females could discriminate between suitable hosts (A. smithi) and unsuitable hosts (Aphelinus “L”) both through the pea aphid.

Studies on Host Selection and Host Specificity of the Aphid Hyperparasite Charips victrix (Hymenoptera: Cynipidae). 2. the Bionomics of Charips victrix

The bionomics of Charips victrix (Westwood) when associated with the primary parasites Aphidius smithi Sharma & Subba Rao and Trioxys complanatus Quilis have been examined. This investigation indicates that all developmental stages of A. smithi which occur in nonmummified aphids are attacked. However, only the larval stages are suitable hosts for the development of C. victrix progeny. Several aspects of the development of C. victrix in this host differ from those previously described. Although the development of C. victrix described from T. complanatus is similar to that from A. smithi , the following differences were noted: (1) a few eggs were deposited in the haemocoels of several parasitized and one unparasitized aphid(s), (2) these eggs failed to develop, and (3) T. complanatus embryos were not attacked. Behavioral responses of the spotted alfalfa aphid to C. victrix attacks tend to restrict the ability of the latter to parasitize C. complanatus . A somewhat different behavioral response is observed when the pea aphid is attacked by C. victrix . Both parasitized and unparasitized aphids are investigated by C. victrix females.

Influence of Parasitization on Form Determination in Aphids

PARASITIZATION of the immature stages of some insects and Crustacea is known to result in structural abnormalities in the adults. Examples from insects are the production of ‘intersexes’ in certain Homoptera and Hymenoptera when parasitized by Strepsiptera1, and of ‘intercastes’ of ants parasitized by nematodes2. Unparasitized aphids intermediate in structure between alate and apterous forms have been observed and described a number of times3, and it has now been found that in Aphis craccivora Koch this kind of intermediate can be produced by parasitization of alatiform nymphs by the braconid wasp Lysiphlebus testaceipes (Cresson).