Respondents of the 1986 Broccoli Growers Survey grew an average of 6.2 acres of broccoli in Fall 1986; popular varieties were Green Valiant (87.5% of respondents), Packman and Emperor (62.5%). Less than 5% of tobacco land was converted to broccoli production by 62.5% of the growers. Before heading, 2.4 insecticidal sprays were applied for worms at $20.51/acre. During heading, 2.4 insecticidal sprays were applied for worms at $19.40/acre. Under normal growing conditions, a nine-day mean of 8.4 and a 15-day mean of 12.1 cabbage looper larvae/plant did not significantly reduce yield in the Spring and Fall respectively. However, means of 7.4 and 11.1 cabbage looper larvae/plant reduced yield (head weight) under drought conditions. Harvest date was not affected by the above cabbage looper levels. In Fall 1986, a reduction in yield occurred when plants had 50% or more defoliation and harvest date was significantly delayed at 100% defoliation. In the drought stressed Spring 1987 planting, a stimulation in yield occurred at 25% defoliation and 75% defoliation was needed to significantly reduce yield, but there was no difference in harvest date. The imported cabbageworm was the most abundant pest of broccoli in Montgomery Co., VA. Based on counts of all immature stages of the insects for three seasons, Packman and Southern Comet varieties were less preferred compared to Green Defender. Laboratory studies indicated that imported cabbageworm larvae developed faster to the fifth instar on Packman broccoli than those reared on Green Defender, Southern Comet or Emperor. Difference in amount consumed between varieties was not detected. Pupae reared on Southern Comet weighed significantly more than those reared on Packman. / M.S.

Hyperparasitism of beneficial parasites of Pieris rapae was studied on Brassica crops in Montgomery County, Virginia. The goal of the study was to determine whether the hyperparasites attacking the larval parasites of P. rapae were capable of eliminating an introduced population of the larval parasite Cotesia rubecula (Marshall) (Hymenoptera: Braconidae). Pieris rapae was found to be active from April to November with possibly six generations per year in this region. It was attacked throughout this period by five generations of the larval parasite Cotesia glomerata (L.) (Hymenoptera: Braconidae). Although P. rapae larvae were twice as numerous on broccoli (var. Premium Crop) than on cabbage (var. Rio Verde), a higher proportion of P. rapae larvae was parasitized by C. glomerata on cabbage, indicating that C. glomerata preferred to forage for P. rapae in cabbage. In spring plantings, up to 36.9% of C. glomerata cocoon masses had been affected by the hyperparasite T. galaetopus (Ratzeburg) (Hymenoptera: (Eulophidae) and 23.3% by the hyperparasite Spiloehaleis torvina Cresson (Hymenoptera: Chalcididae). In the fall, 93.2% and 4.2% of the cocoon masses were affected by T. galaetopus and S. torvina, respectively. Tetrastiehus galaetopus activity was observed from May to November, but it was most active after mid July. Tetrastiehus ga/aetopus had little impact on the gregarious C. glomerata, and even though it could affect >90% of the C. glomerata cocoon masses for extended periods, 500/0 of the cocoons in each mass were unaffected. However, it's high reproductive capacity could adversely affect a solitary host such as C. rubecula. Spilochalcis torvina was observed as early as late May but it was most active during the mid summer months. It's reproductive activity ceased by early October even though hosts were abundant in the month which followed. Four generations were seen between June and October. Spilochalcis torvina's hosts were Cotesia orobenae Forbes (Hymenoptera: Braconidae), C. glomerata, and Plutella xylostella (L.) (Lepidoptera: Plutellidae), but the principal host was C. glomerata. However, the proportion of female S. torvina progenies was <31% from the Cotesia spp. hosts and 70% from P. xylostella hosts. Spilochalcis torvina typically hyperparasitized <4 pupae per Cotesia spp. cocoon mass in the field. In laboratory experiments, S. torvina hyperparasitized an average of <7 C. rubecula pupae daily, and the maximum number hyperparasitized was 12. Due to its apparently low reproductive rate in the laboratory, and its low rate of hyperparasitization on hosts in the field, it is unlikely that S. torvina is a danger to populations of parasites like C. rubecula. / Master of Science

Conura torvina (Cresson) (Hymenoptera: Chalcididae) is a solitary pupal endoparasite of numerous insect species. In Brassica crops it acts as a parasite of Plutella xylostella (L.) (Lepidoptera: Plutellidae) and was found as a hyperparasite of Cotesia rubecula (Marshall) (Hymenoptera: Braconidae) and several other parasitoid species. Cotesia rubecula was introduced into Virginia in 1987 as a biological control agent for Pieris rapae (L.) (Lepidoptera: Pieridae), and because C. torvina was thought to have eliminated this population of C. rubecula, studies of C. torvina's reproductive biology and behavior were initiated. A study using plants laden with "trap hosts" to detect C. torvina activity in the spring indicated no activity until late June, but proved trap host sampling to be an efficient and effective method of monitoring C. torvina activity. Studies of C. torvina's ability to reproduce in C. rubecula pupae of different ages indicated that C. torvina can successfully parasitize pupae at all stages of development, but was most successful in young to middle aged pupae. Studies of C. torvina's host species preference indicated the larger host species such as P. xylostella were preferred. Equal numbers of P. xylostella and C. rubecula were parasitized, but a greater proportion of fertile eggs were laid in P. xylostella. Smaller host species were often ignored. Host dissection studies indicated that caged C. torvina were inefficient at host finding and oviposition. Superparasitism was common, but declined as the females gained oviposition experience. Experienced C. torvina produced an average of 8.25 progenies per day for a period of 12 days when provided with 13 P. xylostella hosts each day. Conura torvina produced up to 14 progenies a day when provided 3 26 hosts. Dissection of C. torvina ovaries indicated three ovarioles per ovary with a mean of 9.2 and maximum of 15 mature eggs per female. Host dissection indicated that a mean of 18 and maximum of 30 eggs could be laid per day. New eggs were produced as oviposition occurred. Significantly larger eggs were laid in P. xylostella than in C. rubecula, and significantly more eggs were laid in C. rubecula than in P. xylostella. From these data and data from earlier studies I concluded that C. torvina has a poor reproductive ability and its impact as a hyperparasite is limited to the summer months. This makes C. torvina an unlikely cause of C. rubecula's disappearance. / Ph. D.

Les cultures de Brassicacées sont très courantes en agriculture urbaine à Montréal. Elles comportent cependant leur lot de problèmes liés aux insectes ravageurs, tels que la piéride du chou, Pieris rapae. L’utilisation de méthodes de lutte classique contre les insectes ravageurs, tels les insecticides, engendrent de sérieux dommages environnementaux, incluant la contamination de l’eau et du sol ainsi que la toxicité pour les plantes environnantes, les insectes auxiliaires et les microorganismes du sol. Le compagnonnage végétal, une pratique agroécologique alternative, est connue en tant que stratégie d’IPM (lutte intégrée contre les insectes ravageurs). L'objectif général de l'étude était d'évaluer in situ l'importance de diverses méthodes de compagnonnage sur l'infestation de P. rapae au sein du chou chinois, Brassica rapa. Les plantes utilisées dans les systèmes de compagnonnage étaient des cultures-pièges (Eruca sativa et Brassica carinata), des plantes compagnes principales qui étaient des plantes insectaires et répulsives pour les insectes ravageurs (Tagetes erecta, Amaranthus cruentus et Ocimum grattissimum) ainsi que des plantes compagnes secondaires (Solanum aethiopicum, Ocimum basilicum et Hibiscus sabdariffa). Les paramètres de physiologie végétale ainsi que les structures des communautés microbiennes et d’insectes ont été suivis de près tout au long de la saison croissance où l’expérience a eu lieu. La taille des larves était significativement plus importante au sein de la monoculture (contrôle) et les taux de concentration de glucosinolates dans les feuilles de Brassica rapa étaient deux fois plus élevés dans les contrôles comparativement aux systèmes de cultures plus diversifiés. Une PERMANOVA a confirmé une différence significative entre les méthodes de cultures concernant la composition des communautés d’insectes bénéfiques. Les communautés bactériennes du sol ont été améliorées par l'agriculture durable par rapport au sol d'origine et ont été bonifiées dans les systèmes de compagnonnage végétal (plus diversifiés). L'étude a mis en évidence les avantages de l'agroécologie, y compris le compagnonnage végétal, en termes de lutte intégrée contre les insectes ravageurs et d'autres composantes de l'agroécosystème. / Brassica crops are very common culture for urban farmers in Montreal where insect pests like the cabbage whitefly, Pieris rapae, are a real concern. The use of conventional insect pest control methods, such as insecticides, causes serious damages to a highly anthropized and therefore already constrained environment. These include air, water and soil contamination, as well as toxicity to surrounding beneficial insects, soil microorganisms, plants and the entire food chain. Companion planting, an agroecological practice, is an alternative strategy for insect pest management. The general objective of the study was to evaluate in situ the relevance of various traditional methods of companion planting on infestation of Chinese cabbage, Brassica rapa, by P. rapae. The plants used in the companion systems were two trap crop species: Eruca sativa and Brassica carinata; Tagetes erecta, Amaranthus cruentus and Ocimum grattissimum were used like companion plants because of their properties as insectary plants and repellent species against the targeted pest; Solanum aethiopicum, Ocimum basilicum and Hibiscus sabdariffa were also considered (secondary) companion plant species. Plant physiological parameters as well as microbial and insect community structure were carefully monitored over the growing season where this experiment took place. Larval size was significantly greater in the monoculture and glucosinolate concentrations in leaves of Brassica rapa was two-times higher in control than in more diversified cultivation systems. With larger yield and the absence of pest in the field, ‘trap cropping system’ was overall the most efficient albeit the 'mix of companion planting’ system had the lowest leaf area damage. A PERMANOVA confirmed a significant difference between the cultivation methods regarding beneficial insect communities’ composition. Belowground, soil bacterial communities were readily modified by sustainable agriculture practice, even more so in biodiversified systems. The study highlighted benefits of agroecology, including companion planting, in terms of integrated pest management and other components of the agroecosystem.