Temperature and host effects on key morphological characters of Hemisarcoptes cooremani and Hemisarcoptes malus (Acari: Hemisarcoptidae)

Abstract

We investigated the influence of temperature and resources on six morphological characters thought to distinguish two North American species of Hemisarcoptes (H. malus and H. cooremani). We raised mites at three temperatures (15, 24 or 30°C) and on two different scale insect prey (Aspidiotus nerii or Aonidiella aurantii) which were cultured on two different substrates (potato tubers and lemon fruit). In general, the temperature had more of an influence on the character variation than did the host and the highest temperature resulted in the smallest mean body size. The two species did not respond to changes in the temperature or host in a symmetrical fashion. The temperature significantly influenced the lengths of the external scapular setae (sce) of H. malus and the sce and first coxal setae (1a) of H. cooremani. The relative lengths of the setae sce and 1a of H. cooremani were significantly influenced by the temperature, while the host type significantly influenced the paraproctal setae (ps ₂). Major-axis regressions indicated that H. cooremani had an absolutely longer mean setal length for 1a and for ps ₂, than H. malus, but a relatively shorter sce. An ANOVA of the size-adjusted shield characters of H. malus resulted in non-significant effects of the temperature or host on either the prodorsal shield area or and area in H. cooremani. Regressions of the shield area (size) on body length, resulted in two clear groupings by species. Hemisarcoptes cooremani had an absolutely larger shield area and increased circumference (complexity), as compared to H. malus. A plot of the shield circumference in relation to the shield area, however, resulted in a single trajectory, indicating that shield complexity is an allometric consequence of an increase in body size in both species. Though characters can be influenced significantly by environmental parameters, the species-specific patterns of some characters of North American Hemisarcoptes are distinctive enough to allow diagnosis and identification.