Stung Hosts Research Articles

Further notes on the biology of Pseudavga flavicoxa Tobias, 1964 (Hymenoptera, Braconidae, Rhysipolinae)

Pseudavga flavicoxa, a solitary koinobiont ectoparasitoid of Bucculatrix thoracella, attacks host larvae early rather than late in their final instar, subsequent development of the parasitoid then occurring within the host cocoon. This paper supplements an earlier contribution outlining other aspects of its biology and taxonomy. The host is stung repeatedly, both into the thoracic region and elsewhere on its body, causing temporary paralysis and also enabling host-feeding, which preceded oviposition in all observed cases. Stung hosts then intercepted without oviposition occurring recovered and (like parasitized hosts) resumed feeding and then constructed a cocoon, but suffered developmental arrest as a prepupa. The egg is invariably laid onto the arthrodial membrane between the first and second thoracic segments, to which it is glued. This site is first prepared by the female by a to-and-fro motion involving contact by the lower valves of the ovipositor, which are somewhat blade-like and sharp-edged. It is unclear whether dried traces of a ‘glue’, presumably originally liquid, subsequently seen at this site were of host origin resulting from a small wound or arose as a secretion from the female wasp, but the former is suggested. The egg was seen to issue from the extreme base of the ovipositor, at most guided onto the prepared patch by the parted lower valves. Although clearly partly plurivoltine, P. flavicoxa is remarkably long-lived as an adult, both sexes being easily kept alive under semi-natural conditions (Edinburgh, U.K.) during the late summer and autumn, males for 8 weeks and females for up to 20, despite their small size (ca 2.2–2.4 mm long). Dissection of gravid females showed that each of the 4 ovarioles carried just one mature egg at a time, with submature eggs remaining only poorly developed until the mature egg was expended.

A comparison of the host‐searching efficiency of two larval parasitoids of Plutella xylostella

Summary1. A host specialist parasitoid is thought to have greater efficiency in locating hosts or greater ability to overcome host defence than a generalist species. This leads to the prediction that a specialist should locate and parasitise more hosts than a generalist in a given arena. The work reported here tested these predictions by comparing the host‐searching behaviour of Diadegma semiclausum (a specialist) and Cotesia plutellae (an oligophagous species), two parasitoids of larval Plutella xylostella.2. Both parasitoids employed antennal search and ovipositor search when seeking hosts but D. semiclausum also seemed to use visual perception in the immediate vicinity of hosts.3. Larvae of P. xylostella avoided detection by parasitoids by moving away from damaged plant parts after short feeding bouts. When they encountered parasitoids, the larvae wriggled vigorously as they retreated and often hung from silk threads after dropping from a plant.4. These two parasitoids differed in their responses to host defences. Diadegma semiclausum displayed a wide‐area search around feeding damage and waited near the silk thread for a suspended host to climb up to the leaf, then attacked it again. Cotesia plutellae displayed an area‐restricted search and usually pursued the host down the silk thread onto the ground.5. Diadegma semiclausum showed a relatively fixed behavioural pattern leading to oviposition but C. plutellae exhibited a more plastic behavioural pattern.6. The time spent by the two parasitoids on different plants increased with increasing host density, but the time spent either on all plants or a single plant by D. semiclausum was longer than that of C. plutellae. Diadegma semiclausum visited individual plants more frequently than C. plutellae before it left the patch, and stung hosts at more than twice the rate of C. plutellae.7. The results indicated that the host‐location strategies employed by D. semiclausum were adapted better to the host's defensive behaviour, and thus it was more effective at detecting and parasitising the host than was C. plutellae.

Apparent Fate of Gypsy Moth (Lepidoptera: Lymantriidae) Pupae Stung by the Introduced Parasite Coccygomimus disparis (Hymenoptera: Ichneumonidae)

Observations on stinging behavior of Coccygomimus disparis (Viereck), an introduced pupal parasite of the gypsy moth, Lymantria dispar (L.), and its impact on host fate were made in a field study at 3 sites in a forested community near Hartly, DE. Incidence of ichneumonid parasitism and other mortality sources were compared in hosts known and not known to have been stung by C. disparis . Both parasitism and other mortality were higher in stung pupae. Survival of pupae, as evidenced by emergence of adult moths known to have been stung by C. disparis , was significantly lower than those not known to have been stung at 2 of the 3 study sites, and at all 3 sites when only female pupae were considered. The only site where no difference was noted had sustained heavy mortality (>80%), induced by other factors, especially Calosoma sycophanta (L.) and Brachymeria intermedia (Nees). Parasitization by ichneumonids and B. intermedia , as well as incidence of disease and desiccation, were higher in pupae of L. dispar experimentally stung by C. disparis than in those which were not. Attacks by C. disparis ranged from 10 s to a17 min in duration, but averaged <4 min. Host feeding by C. disparis females did not affect survival in stung hosts but did prolong attack duration. Attack duration differed among sites.

Protein expression during parasite redirection of host ( Trichoplusia ni) biochemistry

Expression of proteins during normal egg and larval development of Trichoplusia ni was compared with that occurring in hosts stung as eggs by the parasitic wasp Chelonus sp. near curvimaculatus. Those stung hosts which produced a parasite (truly parasitized), precociously expressed proteins associated with larval-pupal metamorphosis, as did those stung hosts which did not contain a developing endoparasite (pseudoparasitized). No highly abundant, low-intermediate molecular weight hemolymph proteins were observed in truly or pseudoparasitized larvae which did not also occur at some point in the development of normal larvae. A low abundance, high molecular mass (160,000 Da) protein was observed in the hemolymph of truly parasitized larvae, but not of normal or pseudoparasitized larvae. The protein is glycosylated and very acidic (pI near 4.5). The data show that any parasitization proteins injected or induced by the ovipositing female parasite are in low abundance, in contrast to situations reported for parasitic wasps which sting hosts as larvae.

Parasite regulation of host insect metamorphosis: a new form of regulation in pseudoparasitized larvae of Trichoplusia ni.

When eggs of Trichoplusia ni (lepidoptera) are stung by a parasitic wasp, Chelonus sp., the developing host larvae precociously initiate metamorphosis ten days later. Precocious initiation of metamorphosis occurs even in 'pseudoparasitized' stung hosts which contain no living parasites at the time of symptoms of host regulation by the parasite. In feeding, penultimate instar, pseudoparasitized hosts, the corpora allata activity, hemolymph juvenile hormone esterase activity, in vivo rates of juvenile hormone metabolism and changes in hemolymph protein composition all follow the pattern of the normal last instar. This and other evidence suggests the entire developmental pattern of the last larval instar is precociously expressed in penultimate instar, pseudoparasitized hosts. The cause of precocious expression of the developmental program leading to metamorphosis is a significant decrease in the critical size parameter that, in normal larvae, signals attainment of the last instar. The induction, in preultimate instar larvae, of the entire feeding stage developmental program leading to metamorphic commitment, using either biochemical, surgical or parasitic experimental probes, has not been previously reported. The results have important implications for the study of host-parasite endocrine interaction, of normal insect metamorphosis and even of human puberty.

Endocrine Interaction between Host (Lepidoptera) and Parasite (Cheloninae: Hymenoptera): Is the Host or the Parasite in Control?

Parasitic wasps of the subfamily Cheloninae (Braconidae: Hymenoptera) have been thought by most previous researchers to be under the endocrine control of their lepidopteran hosts. The current hypothesis that these parasites wait passively until the host begins to metamorphose incorrectly emphasizes the host as the dominant partner. Recent data demonstrate that, in contrast, some Chelonus species actively regulate the metamorphosis of their host. For example, host larvae are induced by the parasite to initiate metamorphosis precociously, but then halt the metamorphic process midway through. These expressions of parasite regulation of the host occur even in stung hosts that contain no parasite at the time the endocrine disruptions become manifest. In light of this information, I examined previous studies on this group of parasites, and found that the entire subfamily Cheloninae should serve as a model of host/parasite interaction in which the parasite is dominant.