Pest management of the New Zealand flower thrips Thrips obscuratus (Crawford) (Thysanoptera: Thripidae) on stonefruit in Canterbury, New Zealand

Abstract

The New Zealand flower thrips (Thrips obscuratus (Crawford)) is an important pest of stonefruit during flowering and at harvest in New Zealand. The biology and control of this species formed the basis for this study.

A simple method for laboratory rearing is described that facilitated studies on the bionomics of T. obscuratus. Aspects of reproduction, fecundity, requirements for oviposition and development, development rates, temperature thresholds, thermal constants, and lifespan are detailed.

T. obscuratus has been reported from at least 223 endemic and introduced plant species. Larvae were taken from 49 species around Canterbury. Adults were usually found on flowers but were also common on leaves and fruits. All larvae were on flowers except for two records from the fruit of stonefruit.

The number and species of thrips infesting sprayed and unsprayed stonefruit flowers and fruit were determined. Adults and larvae were almost all T. obscuratus and adults were mostly female.

Adults and larvae of thrips were found in stonefruit flowers from pink to shuck fall. Adults were found in similar numbers throughout flower development. Larvae were almost entirely absent at pink; numbers were small at full bloom and peaked at or just after petal fall.

Thrips adults, eggs and larvae were all common on peaches, nectarines and apricots. Thrips were most numerous on ripe fruit, although they were found on fruit for the local market up to three weeks before harvest. Thrips numbers were highest on stonefruit varieties ripening during December and January and lowest on varieties ripening during February, March and April, and were higher on peaches than apricots and nectarines.

Sources of T. obscuratus infestations were probably from flowers in the vicinity of the orchard.

Pupation sites for T. obscuratus were established as including the soil and litter beneath a flowering cabbage tree (Cordyline australis).

Female T. obscuratus were parasitised and sterilised by a nematode thought to be Howardula aptini.

Flying thrips were sampled inside and outside stonefruit blocks from September 1984 to August 1987. Several species including T. obscuratus, Thrips tabaci, Limothrips cerealium and Haplothrips niger were common. A broad pattern of the seasonal abundance of T. obscuratus was apparent from water trap samples. Thrips numbers were lowest in winter and low in spring, but increased gradually during summer. Numbers peaked in midsummer but declined suddenly in mid to late January. Numbers remained moderate to low throughout late summer and autumn. Seasonal abundance could be largely explained by the interrelationship of temperature, soil moisture and availability of host plants. Flight take-off thresholds of 15°C were established from weekly water trap samples for both male and female T. obscuratus adults.

Both adults and larvae of T. obscuratus were found on hosts throughout the year, but were most common in early summer. There was no reproductive diapause for T. obscuratus females collected from the field in winter.

In field experiments T. obscuratus males and females showed a preference for white without U.V., and to a lesser extent yellow, compared to green, blue, black and red. Traps baited with ethyl nicotinate caught significantly more T. obscuratus males and females than traps baited with anisaldehyde, benzaldehyde, peach juice, peach fruit and unbaited traps.

An insecticide trial investigated the protection of nectarine flowers from thrips infestation and damage, using the insecticides fluvalinate or phosalone (low toxicity to bees) applied at full bloom as supplements to the current recommended spray programme. Thrips numbers were reduced, and export packout (based on russet only) was 10% higher for trees treated at full bloom than for those treated only with the recommended spray programme.

Several varieties of ripe stonefruit picked at maturity for the local market and which had received only periodic applications of carbaryl were infested with adults, eggs and larvae.

The application of low rates of fluvalinate for preharvest control of thrips on peach fruit was investigated. Peaches were sampled for thrips at local market maturity ('Redhaven') and export market maturity ('Flamecrest'). Low rates of fluvalinate (20% to 5% of field rates) reduced thrips infestation on both varieties. On 'Flamecrest' one application of fluvalinate at 10% field rate, 15 days before harvest, was more effective at reducing thrips infestation than the current recommended spray programme. .

The management of T. obscuratus on stonefruit in Canterbury is reviewed in relation to previous research and knowledge gained from this study.