Green peach aphid, Myzus persicae (Hemiptera: Aphididae), reproduction during exposure to sublethal concentrations of imidacloprid and azadirachtin

BACKGROUND

Resurgence of insect pests following insecticide applications is often attributed to natural enemy disturbance, but hormesis could be an alternative or additional mechanism. Green peach aphid, Myzus persicae (Sulzer), is an important insect pest of many crops worldwide that may be exposed to sublethal insecticide concentrations over time. Here, the hypothesis that exposure to low concentrations of imidacloprid and azadirachtin can induce hormetic responses in M. persicae is tested in the laboratory.

RESULTS

When insects were exposed to potato leaf discs dipped in sublethal concentrations of insecticide, almost all measured endpoints-adult longevity, F1 production, F1 survival and F2 production-were affected, and a statistically significant (P < 0.05) stimulatory response was recorded for F2 production following exposure to imidacloprid. No other measures for hormesis were statistically significant, but other trends of hormetic response were consistently observed.

CONCLUSIONS

Given that variable distribution and degradation of insecticides in the field would result in a wide range of concentrations over time and space, these laboratory experiments suggest that exposure to sublethal concentrations of imidacloprid and azadirachtin could stimulate reproduction in M. persicae.

The stress and fear levels of microwave toe-treated broiler chickens grown with two photoperiod programs

The current study was conducted to investigate the influence of microwave toe treatment and an increasing photoperiod on stress and fear levels in broiler chickens. Upon delivery from the hatchery, the toe tips of 364 male and 364 female broilers were exposed to microwave energy to restrict claw growth, whereas the same numbers of birds retained intact toes. Birds from each sex and toe treatment were grown under 23 h of light or increasing photoperiods, with 4 replicates of each treatment combination. Elevated activity of plasma creatine kinase (CK) and increased heterophil to lymphocyte (H/L) ratios were employed as indicators of stress. Tonic immobility (TI) was conducted on d 10, 22, and 36 and used as an index of fear response. Males had lower plasma CK activity and H/L ratios (P < 0.05). Birds on 23 h of light had a higher activity of plasma CK (P < 0.05) but similar H/L ratios compared with birds on the increasing photoperiod. Microwave toe treatment did not affect the activity of plasma CK or H/L ratios. Photoperiod, microwave toe treatment, or sex did not affect the number of attempts required to induce TI. The increasing lighting program decreased the duration of TI on d 10 (P < 0.05), had no effect on d 22, and increased duration of TI on d 36 (P < 0.05). There was no microwave toe treatment or sex effect on the duration of TI at any ages tested.

Productivity of grazing Holstein cows in Atlantic Canada

The feasibility and profitability of management-intensive grazing (MIG) in Atlantic Canada was studied. Productivity of MIG plus concentrate (1 kg:3 kg of milk) was compared with that of confinement feeding (Confined) using haylage (1996) or corn silage (1997) as 50% of dry matter (DM) in a total mixed ration (TMR). Each year, two groups of 10 Holsteins were used. In 1996, pasture CP content increased from 15.2 to 18.0% of DM, while those of acid detergent fiber (ADF) and neutral detergent fiber (NDF) decreased (33.6 to 23.8%, and 55.6 to 35.4%, respectively) between July 10 and August 28. In 1997, pasture crude protein (CP) content decreased from 30.0 to 15.7%, while ADF and NDF increased (24.9 to 35.8% and 53.5 to 67.4%, respectively) from June 16 to July 14. Because pasture biomass was reduced by winter-kill followed by drought in 1997, MIG cows were supplemented with TMR. Estimated pasture DM intakes ranged from 14.2 to 18.1 kg/d per cow. Milk yields averaged 29.5 and 30.4 +/- 0.43 kg/d in 1996 and 32.5 and 31.8 +/- 0.61 kg/d in 1997 for Confined and MIG cows, respectively. In 1996, the dietary treatment x time interaction was significant. Cows in MIG had higher yields than those in Confined later in the trial, while fat and CP concentrations were usually lower in milk from MIG cows. Lower body weights resulted with MIG. Few differences between production systems were significant in 1997. Milk revenue (Canadian $/d) from Confined cows was higher (14.03 vs. 13.77 in 1996 and 16.10 vs. 15.39 in 1997), but partial profitability of the MIG system was marginally greater in both years.