The effect of phytophagous beetles on plant succession in an old—field community in southeastern Ontario was investigated over a 5—yr period. An experimental comparison of insecticide treated and untreated plots indicates that grazing by Trirhabda spp. on the goldenrod Solidago canadensis resulted in a reduction in precent cover of this species (from 40—70% to °1%), and a significant increase in percent cover of a number of earlier stage successional species.
Females of the solitary aphid parasitoids Aphidius ervi Haliday and A. smithi Sharma & Subba Rao (Hymenoptera: Aphidiidae) discriminated between unparasitized pea aphids and those parasitized by the other species. Oviposition restraint varied with the attack sequence and the length of the interval between successive attacks. The tendency to reject a previously parasitized host increased with interval length; A. smithi females rarely oviposited in aphids that had been parasitized > 30 h earlier by A. ervi. Early first-instar larvae ofA. ervi physically attacked and killed older A. smithi larvae, and older A. ervi larvae killed younger A. smithi, possibly by physiological suppression. Neither species appeared to have a competitive advantage when their eggs hatched at the same time. The evolution of heterospecific host discrimination in A. ervi and A. smithi is discussed. It is suggested that avoidance of multiparasitism is adaptive for both parasitoid species: for A. smithi because it is the inferior larval competitor, and for A. ervi because immatures develop more slowly in multiparasitized than in initially unparasitized hosts.
Oviposition by a parasitoid wasp in an already parasitized host (= superparasitism) may result in larval competition and the loss of offspring. Consequently, in solitary species, the decision to superparasitize should be based on the probability of offspring survival. Females of Aphidius ervi Haliday and A. smithi Sharma & Subba Rao (Hymenoptera: Aphidiidae), two parasitoids of the pea aphid, discriminated between conspecific‐ and heterospecific‐parasitized hosts. Both species showed partial preference for aphids previously attacked by A. smithi, a result predicted from the fact that A. ervi is superior to A. smithi in larval competition under most conditions. Females of A. smithi selectively attacked conspecific‐parasitized pea aphids when given a choice between these and self‐parasitized hosts. Results indicated that females of both species responded to an external pheromone‐like marker to discriminate between self‐, conspecific‐ and heterospecific‐parasitized aphids. In addition, A. smithi may use internal cues to recognize, and avoid oviposition in, aphids previously parasitized by A. ervi. Résumé La décision de superparasiter basée sur la survie larvaire: compétition entre les parasites du puceron du pois Aphidius ervi et Aphidius smithi L'oviposition par une guêpe parasite dans un hôte qui a déjà été parasité (= superparasitisme) pourrait conduire à une compétition entre larves et à une perte de progéniture. Par conséquent, dans les espèces solitaires, la décision de superparasiter devrait être basée sur la probabilité de survie de la progéniture. Les femelles de Aphidius ervi Haliday et de A. smithi Sharma & Subba Rao (Hymenoptera: Aphidiidae), deux parasites du puceron du pois, ont discriminé entre les hôtes parasités par des individus de la même espèce et ceux parasités par des individus d'une espèece différente. Les deux espèces de parasite ont montré une préférence partielle pour les pucerons préalablement parasités par A. smithi, résultat qui était prévisible du fait que, dans la majorité des cas, A. ervi est supérieur à A. smithi dans la compétition entre larves. Les femelles de A. smithi ont sélectivement attaqué les pucerons parasités par un individu de la même espèce lorsqu'il leur était donné de choisir parmi ceux‐ci et ceux parasités par les même individu. Les résultats indiquaient que les femelles des deux espèces répondaient à une sorte de phéromone externe pour distinguer les pucerons parasités par le même individu de ceux parasités par un individu de la même espèce et ceux parasités d'une autre espèce. En plus, A. smithi pourrait utiliser des signaux internes pour reconnaître et éviter l'oviposition dans les pucerons préalablement parasités par A. ervi.
There is increasing evidence that short-range reproductive behaviors of phytophagous pentatomid bugs are mediated by vibrational signals. These signals have not yet been examined for bugs in the genus Euschistus, which contains several species native to the Americas. Substrate-borne vibrational signals (songs) were recorded from both sexes of the Consperse stink bug, Euschistus conspersus Uhler, an economically important agricultural pest in western North America. Females produced two songs (FS-1 and FS-2), each consisting of a series of frequency-modulated pulses with a pulse duration of 352 ± 105 (mean ± SD) and 163 ± 36 ms, respectively. Males produced four distinct songs, two composed of frequency-modulated pulses (MS-1 and MS-3), one consisting of narrowband pulses (MS-2), and one composed of a series of 1–6 short pulses, many of which were fused to form distinct pulse trains (MS-4). For both males and females, songs consisting of very short, frequency-modulated pulses (FS-2 and MS-3), with a mean pulse duration <170 ms, were emitted when the other member of the pair was silent. Songs made up of longer, frequency-modulated pulses (FS-1 and MS-1) were produced spontaneously and in response to songs from conspecifics. Pulses of MS-2 were produced by a male once a duet with a female had been initiated. This song had no frequency modulation and a longer mean pulse repetition time than MS-1. The two female songs and three of the male songs (MS-1, MS-2, and MS-3) were produced during the calling phase of mating behavior. Pulse trains of MS-4 were emitted during close-range courtship. During copulation males produced intermittent pulses of MS-1, the function of which is unknown. Dominant frequencies of all songs ranged from 102 to 136 Hz, comparable with those of other pentatomid songs. Although there were superficial similarities in the song structures of E. conspersus when compared with those of other pentatomid species, the song repertoire of E. conspersus was distinct and unique.
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