Biocontrol introduction
Target pest: Coleophora spissicornis (Lepidoptera: Coleophoridae), banded clover casebearer
Agent introduced: Bracon variegator (Hymenoptera: Braconidae)
Imported:
1961, 1962, 1968, 1969
Import source:
1961, 1969 near Freiburg, Germany; 1961, 1962, 1968, 1969 Avignon, France via Delémont, Switzerland
Import notes:
Cameron et al. (1993) - Bracon variegator was imported as field-collected, encased, fourth instar host larvae, either Coleophora frischella or C. deauratella (closely related to C. frischella [both C. frischella and C. spissicornis are pests of clover in New Zealand and both are hosts for B. variegator] and thus it was thought could serve as a source of parasitoids for C. frischella and C. spissicornis [it is not recorded if any B. variegator emerged from C. deauratella larvae]). Coleophora deauratella, collected from near Freiburg, Germany, were imported in 1961 and 1969;C. frischella were collected from Avignon, France in 1961, 1962, 1968 and 1969 and reared in Delémont, Switzerland prior to shipping to New Zealand. A breeding colony of B. variegator, established from the 1961 importations, produced 57 females and 98 males for release. The 1962 shipment produced six female and nine male B. variegator which were released, prior to the shipment being destroyed because of an infestation of the mite Pyemotes zwoelferi. In 1968, at total of 3,570 encased C. frischella was received in three consignments in October, November and December, and another consignment received in 1969. The intent of the 1968 and 1969 consignments was to establish breeding colonies of other parasitoids, but B. variegator was reported as being present (from pre-shipment dissections an estimated 70 in 1969), although there is no record of B. variegator emergence from these larvae.
Released:
1961
Release details:
Cameron et al. (1989) - in 1961, 57 females and 98 males plus an unknown number of larvae (in ten clover plants, each infested with more than 100 Coleophora spp. larvae, planted into infested clover areas) were released at Nelson, South Island. Six females and nine males were released at Nelson in 1962. Although there is no record of B. variegator emergences or releases from the 1968 and 1969 importations [see Cameron et al. (1989) entry in 'Import notes' section] a DSIR list of parasitoid releases against Coleophora spp. from 1966 to 1970 includes B. variegator and the 1968 and 1969 shipments are the only ones from which these releases could have been made. Following establishment in Nelson, B. variegator were collected from the field there and released in Canterbury, South Island, at Lincoln (10 pairs in 1967; 2,450 individuals, including 1,015 females, in 1968) and Cheviot (50 pairs in 1968).
Establishment:
Cameron et al. (1989) - establishment at Nelson was confirmed in March 1966. Establishment was confirmed at Lincoln in April 1970 and two years later a study there found 26.9% of fourth instar Coleophora spp. [C. frischella and C. spissicornis] parasitised by B. variegator. Found to be established at Palmerston North, North Island in 1981.
Impacts on target:
Cameron et al. (1989) - sampling in Canterbury white clover seed crops showed a ten-fold reduction in Coleophora spp. populations between 1969-70 and 1977. Much of this reduction can probably be attributed to B. variegator although other factors will have contributed, namely a change in clover seed crop management practices and insecticide sprays for the newly established aphids Acyrthosiphon kondoi and A. pisum. Of the parasitoids introduced against Coleophora spp. [C. frischella and C. spissicornis] only B. variegator and Chrysonotomyia trifolii [established in 1977] have established. While they were not deemed the most desirable, in the absence of competition from the parasitoids more closely synchronised with the hosts, B. variegator and C. trifolii have achieved the aim of controlling Coleophora spp. admirably. It is now rare for Coleophora spp. infestations in white clover seed crops to reach an economically damaging level or require control with insecticides.
Cameron et al. (1993) - Bracon variegator, in conjunction with Neochrysocharis trifolii [see the N. trifolii introduction entry], is categorised as exerting “substantial” control (defined as “other control measures are only occasionally required”) over Coleophora spp. [C. frischella and C. spissicornis].
Kaur et al. (2024) - prior to the introduction of two biocontrol agents [B. variegator and Neochrysocharis trifolii] in the 1960s, the clover-feeding moths Coleophora frischella and C. spissicornis seriously hindered red and white clover seed production in New Zealand. These biocontrol agents were highly successful, resulting in the total suppression of clover casebearer seed pests until the arrival of Coleophora deauratella, first detected in New Zealand in 2016 [see Kaur et al. (2024) entry in ‘Non-target impacts’ section below].
Impacts on non-targets:
Kaur et al. (2024) - Bracon variegator, along with Pteramalus puparum and Eupelmus messene [biocontrol agents introduced against Pieris rapae (cabbage white butterfly) and Mayetiola destructor (hessian fly), respectively], has been found associated with fourth instars of the Coleophora deauratella collected from two red clover seed fields in New Zealand. Coleophora deauratella (red-clover casebearer moth) is an invasive pest first detected in New Zealand in 2016 and responsible for red clover seed losses of 80-99.5% in mid-Canterbury in the growing season of 2016-17. However, C. deauratella populations have declined since 2018; the actions of these biocontrol agents may have contributed to this, along with other possible factors such as mechanical crop management practices, climate and C. deauratella population genetics.
References
Cameron PJ, Hill RL, Bain J, Thomas WP (1989). A Review of Biological Control of Invertebrate Pests and Weeds in New Zealand 1874-1987. Technical Communication No 10. CAB International Institute of Biological Control. DSIR Entomology Division. 424p.
Cameron PJ, Hill RL, Bain J, Thomas WP (1993). Analysis of importations for biological control of insect pests and weeds in New Zealand. Biocontrol Science and Technology 3(4): 387-404 https://doi.org/10.1080/09583159309355294
Kaur N, Anderson NP, Dorman SJ, Walenta DL, Donovan BC, Tanner C, Mori BA, Otani J, Sim RE, Rolston P, Faulkner J (2024). Biology and management of Coleophora deauratella (Lepidoptera: Coleophoridae) in red clover seed-growing regions in North America and New Zealand. Journal of Integrated Pest Management Volume 15, Issue 1, 2024, 10 https://doi.org/10.1093/jipm/pmae002
