Biology of a tydeid mite, Homeopronematus anconai (n. comb.) (Acari: Tydeidae), important in San Joaquin Valley vineyards

Abstract

The taxonomy of Homeopronematus anconai (Baker 1943), new combination, is reviewed, and Homeopronematus vidae André 1980 is designated a new synonym. The tydeid mite H. anconai has an egg, one larval, and three nymphal stages. Each postlarval stage begins with a prolonged period of quiescence following apolysis and preceding ecdysis. Quiescent phases are approximately as long as active immature phases. After adult female ecdysis, there is a short preoviposition period followed by a long reproductive period, during which up to 66 eggs per female are laid. When ample food is present, most of the eggs are laid early in the reproductive period. Mean generation time (T) is 20.6 days at 24 °C and 11.8 days at 30 °C. Reproduction is arrhenotokous: unmated females produce male offspring only. The sex ratio is female-biased. An overall estimate of sex ratio is 2.2 females per male. These mites have a clumped distribution in laboratory colonies. Quiescent stages, exuviae, and active larvae and adults are often aggregated near some physical feature such as a leaf vein or cotton strand, but aggregations also occur on otherwise apparently featureless leaf surfaces. Hungry H. anconai females spend more time on leaf surfaces with residues left by other H. anconai females, suggesting that tactile and/or chemical cues produced by the mites themselves may be partly responsible for the aggregation behavior. Female H. anconai have a photoperiodically induced, temperature-sensitive hibernal reproductive diapause. Diapausing females are mated but nongravid and are morphologically distinguishable in appearance from nondiapausing females only because they are nongravid. The primary differences are behavioral: aggregating behavior is marked in diapausing females, and they are less active and feed less than nondiapausing females. The mites are primarily pollen-feeding, and females continue to oviposit only on leaves supplied with pollen. Colonies are easily maintained with pollen provided as food on both blackberry and grape leaves, but not on leaf tissue alone. Attempts to rear H. anconai on pollen on artificial substrates were also unsuccessful. Leaf tissue, while not sufficient for development and reproduction, may provide a necessary nutrient, microhabitat requirement, or ovipositional cue. Other foods utilized include spider mite eggs and fungi. These data allow predictions about field populations of H. anconai. Life table analysis suggests that, during the summer months, populations in the San Joaquin Valley are made up of many (about 10) overlapping generations during April-October. Field populations should increase rapidly when wind-blown pollens are abundant and temperatures are warm. Populations probably survive periods of low pollen availability by using alternate food sources, including spider mite eggs, and by delaying their own egg production. Clumped distributions are expected on grape leaves, and this may result in inbreeding when populations are low. Females that develop in the fall when daylengths are sufficiently short enter a reproductive diapause. Behavioral shifts observed in these females in field cage cultures are probably related to finding, and remaining in, their common overwintering sites under the grape bud scales in vineyards.