NOTES ON THE OCCURRENCE, DISTRIBUTION, POPULATION LEVELS, AND CONTROL OF GRAPHOLITA LIBERTINA HEINR. (LEPIDOPTERA: TORTRICIDAE), A PEST OF LINGONBERRIES IN NEWFOUNDLAND

Grapholita libertina Heinr. larvae are a pest of economic importance in lingonberries (partridgeberries), Vaccinium vitis-idaea L. var. minus Lodd, in Newfoundland. Both domestic and export markets are affected. Surveys conducted during the period 1973–1982 to determine distribution and larval population levels, in localities where berries were harvested commercially, indicated they were infested to varying intensities in all 15 localities studied. Highest infestations occurred at Pouch Cove (5 September 1974 — 122 larvae per kilogram of ripe berries) and on Witless Bay Line (9 August 1977 — 276 larvae per kilogram of green berries).In experiments conducted from 1980 to 1982 at six locations, there was a significant decrease in level of infestation as the crop reached maturity. Our results suggest that delaying the opening of the lingonberry harvest season until the last week of September decreased the risk of infestation.Observations on the life history of G. libertina and a naturally occurring hymenopterous parasite are presented.

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 (Bouché) and Dendrocerus carpenteri (Curtis) in the field.

THE BERTHA ARMYWORM, MAMESTRA CONFIGURATA (LEPIDOPTERA: NOCTUIDAE). MORTALITY OF IMMATURE STAGES ON THE RAPE CROP, 1972–1975

Larvae of bertha armyworm, Mamestra configurata Walk., collected in 1972–75 on rapeseed in the prairie provinces of Canada (predominantly in Manitoba), were killed by one virus, one fungus, one microsporidium, seven insect parasites, and by other factors. Mortality from disease was about 24% in 1972 when bertha armyworm was abundant, but much lower in succeeding years after the host’s population density declined. The most important hymenopterous parasite, Banchus fiavescens Cress., was relatively rare in 1972 but subsequently killed over 40% of the host larvae each year. A tachinid, Athrycia cinerea (Coq.), killed over 20% of the mature bertha armyworms in each generation. Each of the other five parasite species was associated infrequently with M. configurata. Details of the biology of each pathogen and parasite are presented. About 12% of the mature host larvae died because they failed to empty the gut, with subsequent penetration of the gut wall by bacteria, or because they did not form a morphologically-sound pupa. Pupae of M. configurata died in the soil following penetration of the gut wall by bacteria, as a result of soil cultivation, and from low temperatures in winter. No pathogens or parasites were recorded in field-collected pupae, though an ichneumonid, Ichneumon canadensis Cress., parasitized pupae in a field cage and may occasionally do so in natural conditions. No pathogens or parasites of bertha armyworm eggs were recorded. A preliminary survival model for bertha armyworm, based on estimates of mortality from various causes identified in this study, is presented. The possibility of preventing or reducing future oubreaks of M. configurata by colonizing additional parasite or pathogen species in the prairie provinces is discussed.

Cellular immune reactions of larvae of Drosophila algonquin

The haemocytic reactions of larvae of Drosophila algonquin leading to encapsulation and melanization of eggs of the hymenopterous parasite Pseudeucoila bochei are characterized in part by the premature mass differentiation of plasmatocytes to lamellocytes. Normally this transformation of blood cells occurs at the time of pupation. The data suggest the haemocytes are stimulated to differentiate by chemotactic means. In susceptible host larvae the parasite appears activately to inhibit the immune reactions by blocking cellular differentiation.

LARVAL COMPETITION AMONG THREE HYMENOPTEROUS PARASITE SPECIES ON MULTIPARASITIZED HOUSEFLY (DIPTERA) PUPAE

Only one parasite species survived on most housefly (Musca domestica L.) pupae multiparasitized by any two of Nasonia vitripennis (Walk.), Muscidifurax zaraptor K. & L., or Spalangia cameroni Perk. N. vitripennis and M. zaraptor were both intrinsically superior to S. cameroni if the attacks on the hosts by their females preceded, were simultaneous with, or followed by up to 48 hours those by females of S. cameroni. N. vitripennis was intrinsically superior to M. zaraptor if its attack preceded that by M. zaraptor by at least 24 hours; M. zaraptor survived when it oviposited before N. vitripennis; and neither species was consistently superior to the other when their attacks were simultaneous or that by N. vitripennis closely preceded that by M. zaraptor. N. vitripennis often survived on multiparasitized hosts because of its rapid development and rapid and thorough host utilization which caused its rivals to starve. In contrast, M. zaraptor’s success was a consequence of its prédation on eggs and larvae of its competitors and to a lesser extent its moderately rapid development and host utilization. S. cameroni was usually intrinsically inferior to both of the other species because, in spite of being predaceous on their larvae, it developed much more slowly and seldom attacked their eggs. The significance of these qualitative characteristics in insect parasites used in biological control programmes is discussed.