David A. J. Teulon

Thysanoptera as Phytophagous Opportunists

The ecological concept of opportunism is defined, and its relevance to the biology of thrips and their ability to colonise ephemeral habitats is discussed. Evolutionary patterns in host-plant exploitation are explored, revealing that thrips generally adopt the dominant elements of a flora and are rarely constrained by host-plant systematic relationships. A few pest species are highly adaptable, feeding on leaf and flower tissue as well as being predators on other arthropods. Scarcely 1% of the 5,000 described species of thrips are serious pests, and most economic literature deals with just four species. Many more thrips are potential pests, and the contribution of various aspects of their biology to opportunism, such as voltinism, vagility, aggregation and reproductive effort, are considered, together with the relevance of this information to pest control strategies.

Host records for the New Zealand flower thrips (Thrips obscuratus (Crawford) Thysanoptera: Thripidae).

The New Zealand flower thrips, Thrips obscuratus (Crawford) (Thysanoptera: Thripidae), is an endemic flower-inhabiting species and was found on at least 225 endemic and introduced plant species. Larvae were taken from 51 species indicating these species were suitable as breeding hosts. Adults were found mostly on flowers, but were also common on leaves and fruit. All larvae were on flowers except for 2 records from the fruit of stonefruit.

Overwintering and Distribution of Western Flower Thrips in the Mid-Atlantic United States

Western flower thrips (WFT), which has caused significant loss of peaches and nectarines in Pennsylvania since 1991, overwinters in south central Pennsylvania. WFT and Frankliniella tritici were monitored season-long in water traps (1992 and 1993) and flower heads of white clover, Trifolium repens L., (1993) in a nectarine orchard. WFT and F. tritici accounted for 87.0 and 10.1%, respectively, of the thrips in water traps. WFT became more numerous than F. tritici after 21 July. In a regional study WFT was recovered on clover in New Jersey, Pennsylvania, Virginia and West Virginia in sites of intensive peach and nectarine production. F. tritici was prevalent in other sites in Pennsylvania and northern Maryland.

Thrips obscuratus: A Pest of Stonefruit in New Zealand

The polyphagous, flower-inhabiting New Zealand flower thrips, Thrips obscuratus is endemic to New Zealand and is an important pest of stonefruit. In spring, feeding by adults and larvae on nectarine ovaries and small fruits results in irregularly shaped blocks of russet, fine scar lines, and fruit distortion. T. obscuratus infests nectarines and peaches at harvest when adults feed and oviposit on the fruit. Feeding damage on mature fruit is usually minor; the main economic concern is contamination of export fruit. Adults and larvae are found throughout the year where host plant flowers are available, but in stonefruit orchards in Canterbury, NZ, thrips numbers peak in midsummer. There is no reproductive diapause so continuous generations can occur. Natural enemies do not appear to have a significant impact on population size. Attributes of T. obscuratus associated with opportunism pose challenging problems for pest management especially during fruit harvest.

Effect of p-Anisaldehyde and a Yellow Color on Behavior and Capture of Western Flower Thrips

Observations in a flight chamber olfactometer and in glasshouses of sweet pepper or tomato suggest a chemokinetic response by western flower thrips (WFT) to p-anisaldehyde rather than a response based on anemotaxis, chemotaxis, or an odor-induced visual response. Yellow water traps baited with p-anisaldehyde increased capture of WFT >10-fold over non-baited yellow traps, and >100-fold over non-baited black traps. Evidence of baited trap interference with nearby non-baited traps was detected, suggesting a need for caution in interpretation of baited versus non-baited trap catches under glasshouse conditions where traps are not adequately spaced.

Position and Abundance of Pear Thrips Eggs in Sugar Maple Flowering and Vegetative Buds

Bud samples were taken from flowering sugar maple, Acer saccharum (Marsh.), during budburst to determine the position and abundance of pear thrips, Taeniothrips inconsequens, eggs in 1992. Buds were stained with acid fuchsin to observe eggs. Peak numbers of eggs were found in mixed male and female flowering buds and exclusively male flowering buds collected on 1 May, and in vegetative buds collected on 14 May. No female flowering buds were collected. Most eggs were located in the petioles of flowering buds and in the leaf veins of vegetative buds. Factors influencing the position and abundance of eggs and the significance of flowering on the population dynamics of pear thrips are discussed.

Predicting Phenology of Pear Thrips Emergence in Pennsylvania Sugar Maple Stands

Spring emergence of adult pear thrips, Taeniothrips inconsequens was monitored with 20-cm emergence traps in five sugar maple sites across Pennsylvania in 1990 and six sites in 1991 and 1992. Arnold’s least variability method and the standard error of prediction method were used to estimate the best start date x base (air) temperature combination among all combinations of 0–15 degrees C. and January 1 to March 1 for heating degree day (HDD) requirements to first and 50% emergence. The results suggest that HDD’s predict pear thrips emergence no better than average Julian date and that emergence is not temperature dependent, an interpretation inconsistent with previous studies of pear thrips and other thrips species. More likely, the relevant measure for thermal summation is soil temperature near the surface, where adults overwinter, rather than air temperature. Also, cessation of pear thrips overwintering may depend on a chilling requirement followed by thermal summation to promote development to emergence. Both possibilities should be explored through additional analyses and experiments.