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Greenhouse studies were conducted in 2003 and 2004 to quantify and compare plant growth and yield of canola in response to simulated and crucifer flea beetle, Phyllotreta cruciferae (Goeze), feeding injury. Seedlings of 2 canola varieties, 357 RR a hybrid and Raider RR an open pollinated, were subjected to simulated and actual crucifer flea beetle feeding injury. Canola growth responses were determined for growth rate, seed yield and percent oil of seed at 10, 30, 50 and 70% injury levels. In both years, differences in canola growth rate responses were significant between the injury types and ranged from 2.6–14.9% across injury levels. Differences in growth responses for yield (i.e., seed yield and percent oil content) were significant between simulated and insect injury and ranged from 3.1–33.5% in 2003, and 1.3–67.9% in 2004 across injury levels. Both canola varieties generally showed a greater response in growth rate and yield parameters in response to simulated than crucifer flea beetle feeding injury. Simulated feeding injury tested in this study did not adequately mimic actual P. cruciferae feeding injury. Therefore, until an appropriate technique is found, mechanical injury cannot be relied on to substitute for P. cruciferae feeding injury.

Laboratory experiments were conducted to determine the effect of wounding the cotyledons of Sinapis alba L. cv. Ochre, Brassica napus L. cv. Westar, B. rapa L. cv. Tobin, and C8711, a selection from Tobin, on subsequent feeding damage by the flea beetle, Phyllotreta cruciferae (Goeze). Cotyledons of 7-day-old seedlings were wounded either by puncturing them with needles (mechanical wounding) or by exposing them to flea beetles. One, 2, or 9 days following wounding, the wounded and unwounded seedlings were exposed to flea beetles and the feeding damage was estimated as a measure of antixenosis. Mechanical wounding of one of the cotyledons with 96 needle punctures induced a significant reduction in the damage of the unwounded cotyledons of S. alba, 1 or 2 days following wounding. True leaves of the wounded seedlings also showed consistently less damage than unwounded controls, 9 days following wounding. In S. alba, all three levels of mechanical wounding (i.e. 6, 24, or 96 punctures per cotyledon) reduced subsequent flea beetle damage to a similar extent. Wrapping a cotyledon of S. alba with a plastic film produced an effect similar to wounding it with needles. As with mechanical wounding, flea beetle wounding also reduced subsequent flea beetle damage in S. alba. Other plant species (B. napus and B. rapa) tested showed no measurable induced effects on subsequent feeding damage.

Five cycles of single-plant and progeny-row selection in lines derived from Brassica rapa L. "Tobin" were used to identify plants with incomplete resistance to flea beetles, Phyllotreta cruciferae (Goeze). This line, called C8711, had higher survival, grew larger, and yielded more seed than Tobin when the two lines were compared in field plots at Glenlea, Manitoba, unprotected by insecticide. C8711 without insecticide yielded more seed than Tobin treated with a lindane seed dressing, but less than Tobin treated with carbofuran granules. With carbofuran, which prevents most flea beetle damage, the yield of C8711 was 35% higher than for Tobin. At Saskatoon, Saskatchewan, the differences between C8711 and Tobin were not statistically significant, although the trends were similar to those at Glenlea. C8711 was late maturing, produced small seed, and was not of canola quality. The resistance in C8711 is attributed to a low level of antixenosis, rapid growth at the cotyledon stage, and tolerance to damage during the first 3–4 weeks of growth.

The flea beetle Phyllotreta cruciferae (Goeze) is selective of its host plants, both between cultivars and between plants of different ages within cultivars. Previous work has associated these preferences with chemical differences between plants. Factors suspected of affecting P. cruciferae behavior, including host plant chemistry and morphology, were isolated and examined in laboratory assays. P. cruciferae fed equally well on collard and kale cotyledons in both choice and no-choice assays. During 15-min observation periods, flea beetles spent more time on cotyledons than on older leaves of either cultivar. Injured collard and kale cotyledons were fed upon more than uninjured cotyledons in both choice and no-choice assays, and this preference is associated with release of chemical cues from the host. Leaf morphology, however, also affected flea beetle behavior. During 15-min observation periods, P. cruciferae spent more time on 6-wk-old collard leaves than on 6-wk-old kale leaves, and on collard leaf models than on kale leaf models treated with identical leaf extracts. Laboratory results indicate that P. cruciferae host preference is associated with chemical and morphological differences and help explain the spatial patterns in population density observed in the field.

Four himachalene sesquiterpenes and (+)-gamma-cadinene, previously identified as possible pheromone components from males of a North American population of Phyllotreta cruciferae Goeze (Coleoptera, Chrysomelidae), were tested for attractiveness in field trapping experiments in Hungary. A mixture of the four synthetic racemic himachalene derivatives and (+)-gamma-cadinene from a botanical source was slightly attractive to beetles, but much more attractive when blended with the known host-plant-derived attractant allyl isothiocyanate. This result was consistent with a previous study in North America. In tests with optically pure synthetic compounds, a blend of the same himachalene enantiomers found from male beetles was equivalent to the corresponding blend of racemic compounds, whereas a blend of the opposite enantiomers was not active. Through subtraction tests, it was found that the single compound, (6R,7S)-2,2,6,10-tetramethylbicyclo[5.4.0.]undeca-9,11-diene [compound (+)-A in this study], was as active as the whole mixture, suggesting that this compound is the key pheromone component of the European population of P. cruciferae. During field trials, several congeneric species, including P. vittula, P. nemorum, P. nodicornis, and P. ochripes, also were caught, suggesting that the same compound(s) may be relatively widespread as pheromone components in this genus.

Morphological and physical characteristics of plants, such as trichomes (pubescence), surface waxes, silication, toughness, sclerotization, colour, and shape may affect herbivory by providing inhospitable surfaces or by eliciting altered host behaviour (review by Noms and Kogan 1980). Even slight variations in the morphological structure of plants may enhance their fitness and form the basis of resistance. Seedlings of the hybrid cabbage, Brassica oleraceae L. cv. Survivor, provide an intriguing opportunity to study within the same plant the influence of radically different cotyledon morphology on the feeding behaviour of the crucifer flea beetle, Phyllotreta cruciferae Goeze, because a high proportion of seedlings of this cultivar (>92%) have one folded cotyledon. The condition arises from a failure of the inner cotyledon of the embryo to open fully and assume a normal horizontal plane after germination. The outer cotyledon is invariably normal and both cotyledons appear to grow at about the same rate (unpublished data). The degree of folding varies from cotyledons that are only a few degrees from horizontal to those that are fully folded and 90° from horizontal. This study reports the distribution and feeding of P. cruciferae on the morphologically different cotyledons of B. oleraceae cv. Survivor.

The three most important flea beetle pests of western Canadian rape crops appear to be selective in choosing their overwintering sites, as the greatest densities of overwintering adults of Phyllotreta cruciferae (Goeze) and Psylliodes punctulata Melsh. were found in leaf litter and turf beneath hedges and(or) shelterbelts, while that of Phyllotreta striolata (F.) was found in these materials beneath groves of native trees. Most beetles overwintered near the surface in leaf litter and turf rather than in the underlying soil. Within a habitat, sample to sample variation for each species was usually large and the overwintering populations appear to have an aggregated distribution pattern. Winter samples over a 6-year period from all five habitat types combined or from parkland groves reflected the continuously low level of the field population of Psylliodes punctulata, and a marked increase in the field population of P. striolata that occurred in one year. Winter samples taken from hedges and(or) shelterbelts provided little information on population sizes or trends except for indicating the general low level of the Psylliodes punctulata population. Winter mortality was low for all three species. The foregoing information will be useful for developing future sampling plans so that overwintering flea beetle populations can be estimated more reliably.

More than 50% of crucifer-feeding flea beetle (Coleoptera: Chrysomelidae) adults trapped on 1-m column traps in a rutabaga field were taken at less than 20 cm from ground level. The mean length of jump of Phyllotreta cruciferae (Goeze) is 25 cm. Cylindrical traps painted red and coated with Tangletrap were used with statistics of directional data to measure immigration and emigration of adults. There were four immigration episodes and seven emigration episodes during the season.

Mean catches of Phyllotreta striolata (F.) in allyl isothiocyanate baited traps decreased southwards from the boreal forest and northern parkland to the central parkland of Saskatchewan, while the opposite was true for Phyllotreta cruciferae (Goeze). Similar trends in the relative numbers of the two species were evident in sweep net catches in canola crops.

Phyllotreta cruciferae (Goeze), an abundant pest in the parklands, is moderately abundant on the open prairie, less common in the southern parts of the boreal forest, and absent elsewhere in the forest. Phyllotreta albionica LeC. occurs in low numbers in parkland and prairie, and is rare in the forest. Phyllotreta robusta (LeC) occurs in low numbers in the parkland, is rare on the prairie, and was not found in the forest. Psylliodes punctulata Melsh., which has a moderately low population in the parkland, occurs in similar numbers on the prairie and perhaps also in the forest. P. cruciferae will likely cause problems in any cruciferous crops grown on the open prairie and eventually in cruciferous crops in newly-cleared forest areas.

The biology of the crucifer flea beetle, Phyllotreta cruciferae (Goeze), was studied in the laboratory, and under field conditions in southwestern Ontario. Field-collected adults, held in a state of induced hibernation were used for some laboratory studies. A rearing procedure was developed and a culture maintained for eight generations provided additional adults for laboratory work. Development and behaviour of the various crucifer flea beetle stages at different temperatures were studied. The mean preoviposition period ranged from 3.8 (32°C) to 22 (20°C) days. Time required for development from egg to adult varied from 24 (30°C) to 54 (20°C) days. For oviposition capability and egg to adult development, developmental thresholds were ca. 17° and 11°C, respectively, and 61 and 456 degree days were required. Crucifer flea beetle adults overwintered in leaf litter and the top 2.5 cm of soil, in windbreaks, fencerows, and cultivated areas. Adults appeared in early spring. Peak adult movement occurred at this time, primarily within 2 m of the ground, and oriented toward crucifer plots. Using heat unit summations calculated from soil temperatures, adult emergence in the field from eggs set out at various times was predicted with an accuracy of ± 3.7 days. Population studies and heat unit accumulations indicated that there was a single generation of crucifer flea beetle in 1974, and two generations in 1975. Adults were restricted primarily to cruciferous crops, with rutabaga and Chinese cabbage being the preferred hosts, among those varieties tested.

In 1982, the synthetic pyrethroid, cypermethrin, was among the insecticides recommended as a spray for control of adult flea beetles attacking canola crops in Saskatchewan (Saskatchewan Agriculture 1982). Growers reported some problems with its effectiveness at the recommended rates of 14–20 g AI/ha, however, and the recommendation for its use against flea beetles was subsequently discontinued. Laboratory spray trials were begun in 1982 to determine if post-treatment temperature affected the contact toxicity of cypermethrin to adults of the major pest species, Phyllotreta cruciferae (Goeze), and if the dosage that had been recommended was adequate as a contact spray.

During a 1981 study on possible insect vectors of a yeast in Saskatchewan mustard crops, several incidental observations of attack by the western damsel bug, Nabis alternatus Parshley, on adults of the flea beetle Phyllotreta cruciferae (Goeze) were made near Oxbow in the southeastern part of the province. This is the fourth record of insect predation on crucifer-feeding flea beetles in the Canadian prairie provinces. Previous records involved the beetle Collops vittatus Say (Gerber and Osgood 1975), a big-eyed bug, Geocoris bullatus (Say) (Burgess 1977), and larvae of the green lacewing, Chrysopa carnea Stephens (Burgess 1980).

Several instances of predation by lacewing larvae on adults of the flea beetle Phyllotreta cruciferae (Goeze) have been observed in Saskatchewan. Other reported insect predators of rapeseed-crop-infesting flea beetles in the Canadian prairie provinces are the beetle Collops vittatus Say (Gerber and Osgood 1975), and one of the big-eyed bugs, Geocoris bullatus (Say) (Burgess 1977).The first observation of an attack on an adult flea beetle by a lacewing larva was in August 1972, when some lacewing larvae, adult flea beetles, diamondback moth larvae (Plutella xylostella (L.)) and unidentified aphids and midges were swept from maturing rapeseed near Aberdeen, Saskatchewan. One of these lacewing larvae attacked an adult of P. cruczferae in a glass collecting-vial and carried the flea beetle around in its jaws. Other lacewing larvae attacked aphids, midges, and diamondback moth larvae. Further evidence for lacewing larvae feeding on adult flea beetles was obtained in August 1979, when a sizeable population of lacewing larvae in a rapeseed crop was encountered near St. Gregor, Saskatchewan. One of the larvae swept from this crop had an adult of P. cruciferae in its jaws when it was first seen in the sweep net. Later the same day, another lacewing larva, swept from a nearby rapeseed field, attacked an adult of P. cruciferae in a collecting vial. In the laboratory both lacewing larvae, still carrying their prey, were quick-frozen, preserved in 70% ethanol and later photographed.

The length of the developmental period from oviposition to adult emergence for nondiapausing individuals of a solitary endophagous braconid, Microctonus vittatae Mues., was usually about 4 wk at 20°C, 70–80% R.H., and a 16h:8h L:D cycle. However, living second and subsequent instar parasite larvae were occasionally found in adults of Phyllotreta cruciferae (Goeze) and Phyllotreta striolata (F.) (Coleoptera: Chrysomelidae) dissected 25–30 days after parasitization. Most of these beetles also contained one or more dead parasite eggs or first-instar larvae, suggesting that superparasitism prolonged development of the single surviving parasite in each host. Therefore, the effect of superparasitism on the parasite's development was investigated by recording the length of the developmental period of M. vittatae in two groups of adult P. cruciferae, one consisting of a majority of superparasitized individuals and the other mostly of hosts with only one immature parasite each.