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The carrot weevil, Listronotus oregonensis (LeConte) (Coleoptera: Curculionidae), is an insect pest in carrot production in Ontario. The aim of this study was to survey the egg parasitoids attacking the carrot weevil in carrot fields in Ontario, and elucidate the seasonal and chemical ecology of these natural enemies. / Field surveys were conducted during three years in commercial carrot fields in the Holland Marsh and district marshes to detect the presence of carrot weevil egg parasitoids, to determine their geographical distribution and to evaluate the effect of insecticides on the rate of emergence and the activity of parasitoid adults. Two egg parasitoids, Anaphes listronoti Huber and A. victus Huber were found. The dominant species Anaphes listronoti is gregarious, was recovered from most of the sampled fields and was distributed in all sampled marshes whereas the solitary parasitoid A. victus was only sporadically found in the Holland Marsh. These Anaphes species occurred in carrot fields from the end of April to the beginning of September and seasonal parasitism averaged 33% in commercial carrot fields and up to 79% in an untreated plot. The insecticides phosmet, diazinon and cypermethrin used in carrot production, did not affect emergence rate of parasitoid adults indicating that immature stages are protected against insecticide penetration in the host egg. However, insecticide applications decreased parasitism rates and suggest a lethal effect on parasitoid adults by direct contact and insecticide residues, although no difference was observed between treatments. / Laboratory studies were performed to determine the existence of a sexual pheromone produced by female A. listronoti using a four-arm olfactometer. An automated system of insect tracking was developed to quantify male behavior in the olfactometer. The response of males to odor emitted by virgin females less than two days of age was measured. Virgin females less than one-day-old released a long-range pheromone from 4 hours until 16 hours after the onset of the photophase. Females of one and two days of age started to emit the sexual pheromone earlier than younger females.

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Strains of Bacillus thuringiensis active against Coleoptera were evaluated for toxicity against the adult stage of the carrot weevil, Listronotus oregonensis. Mortality and frass bioassays using a suitable semi-artificial diet showed strains A30, A429 and BTT to be highly toxic. Mortality persisted after initial exposure to the bacteria with the survivors not resuming normal feeding. Attempts to reisolate B. thuringiensis from the insects revealed B. thuringiensis-like organisms in the gut and in/on other structures. At the midgut pH of the insect (pH 8.0), the crystals of the toxic strains were significantly more soluble in vitro than were crystals of the less toxic strain A311. Proteolytic activation of the crystals with gut extracts yielded a protein band (66-67 kDa) for strains A30 and A429 which was similar to he apparent molecular weight of the toxin protein for BTT. Evidence suggests that the low toxicity of strain A311 might be due, in part, to the absence of the toxic moiety of the $ delta$-endotoxin.

The carrot weevil, Listronotus oregonensis LeConte (Coleoptera: Curculionidae), is an important pest of carrot in northeastern North America. The objective of this study was to determine the host selection stimuli used by two L. oregonensis parasitoids: the adult parasitoid Microctonus hyperodae Loan and the egg parasitoid Anaphes victus Huber. / In the first chapter, the response of M. hyperodae females to various odor components from potential hosts and host plants was tested with a Y-olfactometer. / In the second chapter, the effect of L. oregonensis adult sex, feces and movement on host selection behavior of M. hyperodae females was evaluated by quantifying L. oregonensis adult movement and various M. hyperodae female behaviors in an arena. / In the third chapter, the response of A. victus females to different L. oregonensis related odor components was evaluated using a filter paper of which half was moistened with odor components and the other half with water.

The time-varying survival rates of the carrot weevil, Listronotus oregonensis, were estimated by a new method. This method precluded the possibility of negative simulation survival rates. Analysis of carrot weevil population dynamics indicated that the egg mortality was density dependent with Anaphes sordidatus, an egg parasitoid, as a major density dependent factor. Larval mortality was less density dependent. Based on the mortality information, a simulation model for carrot weevil population dynamics was established. The simulation precision, evaluated by comparing simulated and observed egg and larval population dynamics, was satisfactory. Sensitivity analysis indicated that A. sordidatus had a large influence on carrot weevil population dynamics. The economic threshold for carrot weevil control in early carrots was 5 eggs/100 carrots at the peak population density. It ranged from 3.8 to 5.3 eggs/100 carrots in mid-season carrots depending on the selling price. A decision model showed that the best sowing date was after June 5 when risks were not considered. For risk aversion growers, sowing carrots between May 20 and May 31 was the best choice.

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No description available.