The weed Galium aparine L. (Rubiaceae), commonly known as cleavers or goose grass, is an exotic plant in New Zealand (Webb et al. 1988; Reid 1998). Craemer et al. (1999) described a new gall mite species, Cecidophyes rouhollahi Craemer (Acari: Eriophyidae), from this weed in France. They suggested that this new species might have potential as a biological control agent against G. spuriumL. in Canada and western US where the weed was becoming more problematic (Malik & Vanden Born 1988; Whitson 1991). This mite species was later shown to result in severe stunting and complete prevention of seed production in a related weed G. spurium in greenhouse tests and was approved for field release against this weed in Canada (Sobhian et al. 2004). This mite species was recently reported on G. aparine from Auckland, New Zealand (Martin 2017). Mites prefer feeding on the young terminal leaves and can induce the leaf edges to roll inwards and curl (Fig. 1A, B, Fig 2B). Martin (2017) noted: “No natural enemies of this species of mite have been recorded, but predatory mites may feed on these mites”. We report here on an assemblage of predatory mites (Phytoseiidae) associated with C. rouhollahi on G. aparine in Auckland.

We observed a large infestation of G. aparine by C. rouhollahi along a canal in Waiatarua Reserve (Fig. 1A & B) and another one in St Johns, Auckland (Fig. 2). We collected about 100 stems of G. aparine from Waiatarua Reserve on 5 December 2017 and all of them were infested with mites. Most upper leaves were rolled or curled. Close examinations of these curled leaves revealed dense coats of hairs and many C. rouhollahi, along with some phytoseiid mites hiding between hairs. The eriophyid mites seemed to provide a certain degree of natural control of the weed. It is unknown if the predatory mites will have a negative impact on the weed biocontrol. It is interesting to note that Galium palustre L., which was close to G. aparine in the same location, was not infested by C. rouhollahi.

To extract gall mites, we sampled 20 terminal stems of G. aparine (10 cm long) haphazardly and placed each stem individually in a glass bottle (diameter 6 cm, length 10 cm). We filled the bottle with 2 cm of 95% ethanol and shook it 100 times. We then removed the stem and filtered the liquid with mites via a piece of filter paper. Under a dissecting microscope, we counted 3236.7 (1000–6700) eriophyid mites per stem.

To collect the phytoseiid mites, we beat 3 groups of ca 20–30 collected stems each over a black plastic sheet (450 × 600 cm) 30 times and collected 38 (34–43) phytoseiid mites per group of stems. We placed 10 of these predators (adult females, not identified) individually in a modified 0.3-cm diameter Munger cell (see Petal & Zhang 2017a,b for details) each with 15 eriophyid mites on a leaf of G. aparine and confirmed predation of 14–15 (average 14.8) eriophyid mites per day. Among the predatory mites collected, we identified five species common in Auckland: Neoseiulus cucumeris (Oudemans, 1930); Amblyseius herbicolus (Chant, 1959); Amblydromalus limonicus (Garman & McGregor, 1956); Neoseiulella cottieri (Collyer, 1964); and Neoseiulella novaezealandiae (Collyer, 1964). No other phytophagous mites were observed on G. aparine. There seemed to be little doubt that the phytoseiids moved from other plants to this weed to take advantage of the super abundance of a new food source. Two of these phytoseiid species are important biocontrol agents and known to feed on eriophyids. Neoseiulus cucumeris could develop successfully on tomato russet mite, Aculops lycopersici (Massee), but failed to reproduce on this prey (Brodeur et al. 1997); whereas A. limonicuscould feed and reproduce on a diet of this eriophyid mite (Houten et al. 2013).

FIGURE 1.

Cecidophyes rouhollahi and Galium aparine (St Johns, Auckland, New Zealand). A. Curled terminal leaves and expanded basal leaves of G. aparine (close-up view); B. Curled leaves of G. aparine in the field; C. Normal leaves of G. aparine.

FIGURE 2.

Cecidophyes rouhollahi and Galium aparine (St Johns, Auckland, New Zealand). A. C. rouhollahiadults and immature stages among leaf hairs (close-up view); B. Close-up view showing curled leaves and dense coat of hairs on them.

The origin of C. rouhollahi in Auckland is unknown. As the damage has never been reported in New Zealand before 2017, it is assumed that this must have been a very recent accidental introduction.The mechanism for this fortuitous accidental introduction is unknown and requires further study. Given the host specificity of these mites, they would likely have needed to have been imported on fresh Galium aparine plant material, because these mites will die very soon when removed from their host. Future studies are needed to assess the spread and effects of the gall mites on the weed. It will be also beneficial to examine at an early stage the possible negative effects of predatory mites on natural biocontrol of cleavers as have been reported for other weed biocontrol systems such as gorse biocontrol, which was disrupted by predators (esp. phytoseiid mites and coccinellid beetles) in New Zealand (Palevsky et al. 2013).

Material examined and vouchered in New Zealand Arthropod Collection. All specimens collected by Min Ma, Li-Xia Xie and Zhi-Qiang Zhang, 5.XII.2017, from Galium aparine L., Waiatarua Reserve, Meadowbank, Auckland: 2♀1♂, Amblyseius herbicolus; 6♀1♂1 deutonymph,Amblydromalus limonicus; 1♀, Neoseiulus cucumeris; 3♀, Neoseiulella cottieri; 1♀, Neoseiulella novaezealandiae.