Feeding and oviposition preferences of the diamondback moth Plutella xylostella (Lepidoptera: Plutellidae) on six Brassicaceae host plant species

Plutella xylostella (diamondback moth, DBM) is a globally distributed Lepidopteran that feeds and oviposits almost exclusively on plants in the Brassicaceae family. DBM disperses from the southern United States and Mexico into Canada in the spring and summer. Establishment of DBM in Ontario is partially dependent upon the quantity and quality of host plants available and the preference of DBM for different hosts. Host plants include many crops such as broccoli, canola and cabbage, as well as landscape ornamentals and wild plants. It has previously been established that DBM are attracted to host plants by chemicals, specifically glucosinolates. I examined the preference of DBM among crop, wild and ornamental host plant species and how preference varies with insect life stage (3rd and 4th instar larvae and adults). Experiments included exposing DBM larvae from five populations coming from different locations in Canada to six Brassicaceae species and evaluating the preferences and weight gain over one hour. Then adult females were exposed to these same plant species and their oviposition preferences were examined. Populations from Alberta, Saskatchewan and Ontario were compared to assess differences in preference associated with geographic region or species of host plant. The ultimate goal of my study was to understand the potential of various Brassicaceae species to act as reservoirs to sustain and promote population growth of DBM, as well as sinks that may decrease DBM abundance. Results showed that garden cress (Lepidium sativum) was highly preferred over other species (wintercress, black mustard, aubretia, broccoli and ornamental kale) for both food and oviposition sources. Previous studies report that garden cress contains saponins, chemicals shown to be toxic to developing DBM larvae, however no studies have yet shown a preference for garden cress. These results provide information on a novel host plant with the potential to control DBM population growth. No difference in preferences was found among populations of DBM from various sources in Canada.

Does Gamma-aminobutyric acid function as a plant resistance mechanism against phytophagous insect activity? /

Gamma-aminobutyric acid (GAB A) is a ubiquitous non-protein amino acid synthesized via the decarboxylation of L-glutamate in a reaction catalyzed by the cytosolic enzyme L-glutamate decarboxylase (GAD). In animals it functions as an inhibitory neurotransmitter. In plants it accumulates rapidly in response to various stresses, but its function remains unclear. The hypothesis that GABA accumulation in leaf tissue may function as a plant resistance mechanism against phytophagous insect activity was investigated. GABA accumulation in response to mechanical stimulation, mechanical damage and insect activity was demonstrated. In wt tobacco (Nicotiana tabacum cv Samsun), mechanical stimulation or damage caused GABA to accumulate within 2 min from mean levels of 14 to 37 and 1~9 nmol g-l fresh weight (FW), respectively. In the transgenic tobacco strain CaMVGAD27c overexpressing Petunia GAD, the same treatments caused GABA to accumulate from 12 to 59 and 279 nmol g-l FW, respectively. In the transgenic tobacco strain CaMVGADilC 11 overexpressing Petunia GAD lacking an autoinhibitory domain, mechanical stimulation or damage caused GABA to accumulate from 180 to 309 and 630 nmol g-l FW, respectively. Ambulatory activity by tobacco budworm (TBW) larvae (Heliothis virescens) on leaves of CaMVGAD27c tobacco caused GABA to accumulate from 28 to 80 nmol g-l FW within 5 min. Ambulatory and leaf-rolling activity by oblique banded leaf roller (OBLR) larvae (Choristoneura rosaceana cv Harris) on wt soybean leaves (Glycine max cv Harovinton) caused GABA to accumulate from 60 to 1123 nmol g-l FW within 20 min. Increased GABA levels in leaf tissue were shown to affect phytophagous preference in TBW larvae presented with wt and transgenic tobacco leaves. When presented with leaves of Samsun wt and CaMVGAD27c plants, TBW larvae consumed more wt leaf tissue (640 ± 501 S.D. mm2 ) than transgenic leaf tissue (278 ± 338 S.D. mm2 ) nine times out of ten. When presented with leaves of Samsun wt and CaMVGAD~C11 plants, TBW larvae consumed more transgenic leaf tissue (1219 ± 1009 S.D. mm2 ) than wt leaf tissue (28 ± 31 S.D. mm2 ) ten times out of ten. These results indicate that: (1) ambulatory activity of insect larvae on leaves results in increased GABA levels, (2) transgenic tobacco leaves with increased capacity for GABA synthesis deter feeding, and (3) transgenic tobacco leaves with constitutively higher GABA levels stimulate feeding.

Parental care in the common tern (Sterna Nirundo): sexual roles in a monogamous seabird

The parental behaviour of male and female Common Terns (Sterna hirundo) was documented throughout two breeding seasons at a colony near Port Colborne , Ontario. Thirteen and fourteen pairs of terns were chosen for intensive study in 1982 and 1983, respectively. The delivery of fish by males to their mates ("courtship feeding") occurred prior-to, during, and following the egg-laying period. Following the laying of the second egg, courtship feeding rates declined significantly. There was a significant, positive correlation bebween courtship feeding rates and subsequent chick feeding rates by males. The incubation rates of females were significantly higher than those of males, especially during the first ten days of incubation. Territorial attendance rates during the incubation stage were similar for males and females. During the chick stage, territorial attendance rates of females were significantly higher than those of males. The size of fish fed to chicks by males increased as the chicks grew older and chick feeding rates of males were approximately three times higher than female rates. Based on these quantitative differences in parental care activities, the cumulative parental time investment by the two sexes was very similar. However, the energetic investment by males was likely greater than that by females, since male parental contributions (e.g. courtship feeding and chick feeding) often entailed extensive foraging behaviour.

The Role of Pyruvate Dehydrogenase Kinase-4 in Post-Exercise Glycogen Recovery

The pyruvate dehydrogenase (PDH) complex regulates the oxidation of carbohydrates in mammals. Decreased activation of PDH following exhaustive exercise may aid the resynthesis of glycogen through increased activity of PDH kinase-4 (PDK4), one of four kinases that decrease the activity of the PDH complex. The purpose of this study was to examine the role of PDK4 in post-exercise glycogen resynthesis. Wild-type (WT) and PDK4-knockout (PDK4-KO mice) were exercised to exhaustion and were sampled at rest (Rest), at exercise exhaustion (Exh), and after two-hours post-exercise (Rec). Differences in feeding post-exercise led to the addition of a PDK4-KO group, pair-fed (PF) with WT mice. Glycogen fully recovered in all Rec groups in muscle however remained low in the PF group in liver. Flux through PDH was elevated in PDK4-KO muscle with feeding and low in the PF group in both tissues. This suggests PDK4 may fine-tune flux through PDH during exercise recovery.