Scanning electron microscopy of foreleg tarsal sense organs of the poultry red mite, Dermanyssus gallinae (DeGeer) (Acari:Dermanyssidae).

Scanning electron microscopy (SEM) studies on the poultry red mite, Dermanyssus gallinae (DeGeer), showed that the tip of the foreleg tarsus of both sexes and early instar stages (larvae, protonymph and deutonymph) bears a cluster of 10 blunt peg-type sensillae. Diversity in size, shape and surface features of the wall of these sensillae characterize the sensilla complex (sensory field). Two short setae (1 and 2) with smooth walls lack detectable pores, whereas three medium-sized setae (4, 5 and 8) bear pores in the wall. Four medium or long setae (3, 6, 7 and 9) have longitudinal grooves or ribs in the wall, whilst one seta (10) possesses both pores and grooves in the wall. Based on the morphology, it is suggested that the porous setae could be olfactory receptors, and the grooved setae could be mechanoreceptors.

Influence of Dermanyssus gallinae and Ascaridia galli infections on behaviour and health of laying hens (Gallus gallus domesticus).

(1) The effect of infections with Dermanyssus gallinae (poultry red mite or chicken mite) and Ascaridia galli (roundworm) on the behaviour and health of laying hens was investigated. (2) Six groups of 15 pullets (Isa Brown) were kept in indoor pens from 18 weeks of age. Two groups were artificially infected with D. gallinae, two groups with A. galli and two groups were kept as uninfected controls. The hens were observed for behavioural reactions and physiological changes (weight gain and various blood variables) to the parasitic infections. (3) Infections with D. gallinae resulted in reduced weight gain, anaemia and even death of some of the hens. Behavioural changes were also observed, as the mite-infected hens showed higher self-grooming and head scratching both during the day and night. (4) A. galli resulted in a lower weight gain but no significant changes were seen in blood variables or behavioural activities.

Activation of the poultry red mite, Dermanyssus gallinae (Acari: Dermanyssidae), by increasing temperatures.

The poultry red mite, Dermanyssus gallinae, is a parasite of layers in Europe. In order to improve our understanding of the host-searching behaviour of these mites their sensitivity to slowly increasing temperatures was studied under laboratory conditions. Temperatures increasing as slowly as 0.005 degrees C/s (over a one min period) were effective in activating the mites. The speed of the temperature change is more important than the temperature change itself for this activation process. This knowledge of the host-searching process could facilitate the development of new control strategies.

Effect of food deprivation on response of the mite, Dermanyssus gallinae, to heat.

Freshly blood-fed adult females of the chicken mite Dermanyssus gallinae DeGeer (Acari: Dermanysidae) were food-deprived during 1, 2-3, 8-10, 14-16 and 22-23 days. These mites were tested in groups of 10 to determine their sensitivity to a heat cue delivered for a 60 s period under controlled laboratory conditions (24 degrees C, simulated dark conditions of 2 lx). Immobile mites were videotaped and start of activation (for individual mites) and percentage of mites activated in the 60 s period were related to temperature changes. Mites were activated with temperature gradients as low as 0.003-0.005 degrees C/s. Mites that had fed the previous day had a significantly lower activation (20%) than other groups. Activation was highest at 2-3 days (60%) and 8-10 days (75%) post-feeding. Activation declined significantly to 45% at 14-16 days and to 30% at 22-23 days post-feeding. Activation patterns probably reflect mite physiological condition and declining responsiveness to heat cues concomitant with starvation and higher risks associated with activation in the prolonged absence of a host.