Mary Carver

Biological and genetic characterization of morphologically similar Therioaphis trifolii (Hemiptera: Aphididae) with different host utilization

The aphid Therioaphis trifolii (Monell) is indigenous to the western Palaearctic region, where it colonizes lucerne (alfalfa), clovers and related legumes. A form of the species, T. trifolii f. maculata (the spotted alfalfa aphid, SAA), has been known in Australia since 1977, feeding almost exclusively on Medicago sativa (lucerne). Since 1989, T. trifolii has been found in Australia colonizing Trifolium subterraneum (subclover). We have compared samples of T. trifolii in Australia collected on lucerne and subclover using several techniques: survival and reproduction on different hosts, morphology, cuticular hydrocarbon profile, karyology, and a combination of RAPD-PCR and mitochondrial DNA (cytochrome oxidase) genetic markers. Whereas there were no distinct differences in cuticular hydrocarbons and karyology, we found significant correlated differences between the host on which aphids were collected, some morphological characters, and the genotypes of the aphids. Aphids collected from lucerne were always of one genetic type, and nearly all those from subclover were of another. Both groups of aphids are morphologically distinguishable from the yellow clover aphid (YCA), the other form of the species recognized so far. We conclude that the clover-colonizers (spotted clover aphid, SCA) and the lucerne-colonizers (SAA) are each host-restricted forms (biotypes) of T. trifolii . Estimates of mtDNA divergence are in the range of conspecific to closely congeneric, as compared with other insects including aphids. We developed simple diagnostic DNA tests to distinguish the two pest aphids.

A new indigenous species of Aphis Linnaeus (Hemiptera: Aphididae) on Muehlenbeckia (Polygonaceae) in New Zealand

The apterous and alate viviparous, and oviparous, female morphs of Aphis cottieri sp. nov. are described from two species of the Gondwanan plant genus Muehlenbeckia in the South Island of New Zealand. Among the characteristic features of this species are: the complete absence of secondary antennal rhinaria; a once-branched media of the fore wing; well-developed frontal tubercles; and the rare to occasional absence of one or both marginal tubercles on abdominal segments I and VII; features that are also present to different extents in several other indigenous Aphidini of New Zealand and Australia. A. cottieri was parasitized by Aphidius sp. near ervi Haliday (Hymenoptera: Braconidae: Aphidiinae)

Studies on the biology of Aphidius sonchi Marshall (Hymenoptera: Aphidiidae), a parasite of the sowthistle aphid, Hyperomyzus lactucae (L.) (Hemiptera: Aphididae)

The hymenopterous parasite, Aphidius sonchi Marshall, has been introduced into Australia as a biological control agent of the sowthistle aphid, Hyperomyzus lactucae (L.), the principal vector of lettuce necrotic yellows virus disease. Some aspects of its biology were studied in the laboratory. Females reared at 22°C contained a mean ± s.e. of 179·4 ± 10·26 eggs on emergence, and more eggs were formed during adult life. Unmated females produced male progeny only; mated females produced progeny of both sexes. At 22°C, both males and females mated within 12 h of emergence. Virgin females could mate successfully after having commenced oviposition and switch to producing progeny of both sexes. At 20°C, both virgin and mated females started oviposition within 7 h of emergence. The female oviposited in all nymphal instars and both apterous and alate adults of the host. Only one egg was laid per insertion of the ovipositor. Superparasitization was common, but only one parasite per aphid survived to the adult stage. Females at 22°C and LD 12:12 oviposited during both the photophase and the scotophase; the proportion of eggs laid in the scotophase was correlated with the availability of hosts. Adult females lived longer in the absence of hosts than in their presence and lived longer than males, and those supplied with water and honey lived longer than those without. Facultative diapause occurred. The integumental coloration of adults varied according to the temperature during their immature stages. Females of A. sonchi oviposited readily in Macrosiphum euphorbiae (Thomas), but their progeny did not develop beyond the egg stage. A. sonchi was parasitized by Alloxysta ancylocera (Cameron), Pachyneuron aphidis (Bouche) and Dendrocerus carpenteri (Curtis) in the field.

THE EFFECT OF TEMPERATURE ON THE ADULT INTEGUMENTAL COLORATION OF APHIDIUS SMITHI

When Aphidius smithi Sharma & Subba Rao (Hymenoptera: Ichneumonoidea) is reared at different constant temperatures, the adults manifest striking but constant differences in integumental coloration, especially in the face, thorax and petiole. Most notably, in females reared at 24°, the face is orangey‐brown and the mesothorax and tergite I are orange‐coloured; at 12°, these parts are black.