J. G. Charles

Mealybugs (Hemiptera: Pseudococcidae) and their natural enemies in New Zealand vineyards from 1993-2009

Mealybugs (Hemiptera: Pseudococcidae) and their insect natural enemies were collected from vineyards in the major winegrowing regions of New Zealand from 1993 to 2009. Mealybugs were identifi ed from 131 separate collections, and their presence on grapevines compared with that on neighbouring citrus trees in Hawkes Bay and Gisborne in 2003. Pseudococcus longispinus and P. calceolariae were the most common mealybugs found in vineyards throughout the country. Both species were present and widespread in most vineyards, and on many grape varieties, but there was often marked (and unpredictable) spatial and temporal separation. Two other mealybug species were found, each on one occasion: the exotic Pseudococcus viburni from Hawkes Bay in 1998, and the endemic Paracoccus abnormalis from Auckland in 2008. Natural enemies were collected or reared from their mealybug hosts from 51 of the collections. Seven species of parasitoids and four species of predators were commonly collected, with no apparent regional constraints. The parasitoids were: Anagyrus fusciventris, Gyranusoidea advena, Tetracnemoidea brevicornis, T. sydneyensis, T. peregrina (all Hymenoptera: Encyrtidae), Coccophagus gurneyi (Hym: Aphelinidae) and Ophelosia charlesi (Hym: Pteromalidae); and the predators were: Cryptolaemus montrouzieri, Midas pygmaeus (Coleoptera: Coccinellidae), Diadiplosis koebelei (Diptera: Cecidomyiidae) and Cryptoscenea australiensis (Neuroptera: Coniopterygidae). The faunas of vineyards and citrus orchards were similar, except that Parectromoides varipes (Hym: Encyrtidae) was collected only from citrus orchards. Linepithema humile, the Argentine ant, was collected from one Gisborne and three Hawkes Bay vineyards in 2003. The widespread presence of natural enemies shows that mealybugs are regularly attacked by both predators and parasitoids in vineyards, but additional data are required to quantify the effectiveness of biological control of mealybugs, and its contribution to limiting the spread of the economically important grapevine leafroll disease.

Using parasitoids to infer a native range for the obscure mealybug, Pseudococcus viburni, in South America.

The co-evolutionary relationships between mealybug hosts (Hemiptera: Coccoidea) and Encyrtidae (Hymenoptera) appear to be particularly strong, and many successful classical biological control programmes against mealybugs have been carried out using these parasitoids. It is a puzzle, then, that the obscure mealybug, Pseudococcus viburni (Signoret) (Hemiptera: Pseudococcidae), is considered to be an American species but is not attacked by native parasitoids in the USA, whereas it is controlled in Europe by Acerophagus maculipennis (Mercet) (Encyrtidae) which was described from the Canary Islands (as Pseudophycus maculipennis). An examination of the biogeographical origins of both the Pseudococcus maritimus complex (to which P. viburni clearly belongs) and the genus Acerophagus Smith, coupled with historical trade records, supports the hypothesis that P. viburni and A. maculipennis are co-evolved Neotropical species, and that both were transported from S. America (probably Chile) to Europe via the Canary Islands on host plants such as potato, possibly as early as the sixteenth century. Invasion of P. viburni into the USA (and elsewhere around the world) occurred later, but without A. maculipennis (or other natural enemies). This explains why P. viburni in the USA is not attacked by native North American parasitoids and why A. maculipennis is not known to attack any mealybugs of Palaearctic origin. The hypothesis adds confidence that well conducted classical biocontrol programmes involving these taxa pose a low environmental risk to native, non-target fauna.

Potential effects of climate change on biological control systems: case studies from New Zealand

Biological control systems are integral to New Zealand’s success as a nation reliant on exporting quality agricultural, forestry and horticultural products. The likely impacts of climate change projections to 2090 on one weed and four invertebrate management systems in differing production sectors were investigated, and it was concluded that most natural enemies will track the changing distributions of their hosts. The key climate change challenges identified were: disparities in natural enemy capability to change distribution, lack of frosts leading to emergence of new pests and additional pest generations, non-target impacts from range and temperature changes, increased disruptions caused by extreme weather events, disruption of host-natural enemy synchrony, and insufficient genetic diversity to allow evolutionary adaptation. Five classical biological control systems based on the introduced species Longitarsus jacobaeae, Cotesia kazak, Aphelinus mali, Microctonus aethiopoides and Microctonus hyperodae are discussed in more detail.

Ant dominance in urban areas

A survey was conducted to determine the distribution of dominant ants and factors that may influence their dominance in New Zealand cities. A new method of active ant trapping combining aspects of pitfall trapping and attraction to food baits was used to capture a sample of all ant species that attended baits. Fifty eight percent of the ant species present in New Zealand were recovered from 2202 traps, with multiple species catches in 245 traps. There was a strong latitudinal relationship in the distribution of ant species, with the proportion of native to introduced species increasing in favour of the native species as latitude increased (south). The presence of Linepithema humile, the Argentine ant, a numerically dominant species was associated with a significant reduction in the number of other ant species captured. With increased urbanisation, providing refugia at times of cool temperatures for warm temperate-sub tropical introduced ant species, their range may extend into the higher latitudes, further displacing native ants from New Zealand cities.

Non-target species selection for host-range testing of Mastrus ridens

The approach taken to selecting non-target species for host-range testing of Mastrus ridens (= M. ridibundus auct.) (Hymenoptera: Ichneumonidae), a proposed biocontrol agent for codling moth, Cydia pomonella (Lepidoptera: Tortricidae) in New Zealand, is described. An initial list of potential hosts was developed, derived from a combination of phylogenetic/taxonomic affinity to codling moth, ecological similarity to codling moth, and ‘safeguard’ or environmental considerations. The species selected, all in the family Tortricidae, were: Cydia succedana and Grapholita molesta (both exotic species in the sub-family Olethreutinae, tribe Grapholitini), the endemic “Argyroploce” chlorosaris (unassigned in the Olethreutinae), and the endemic Ctenopseustis obliquana and Planotortrix octo (both of which are common pest species in the sub-family Tortricinae, tribe Archipini).

Laboratory and field studies supporting the development of Heringia calcarata as a candidate biological control agent for Eriosoma lanigerum in New Zealand

Studies supporting a project seeking to introduce Heringia calcarata (Loew) (Diptera: Syrphidae) to New Zealand (NZ) to supplement biological control of woolly apple aphid (WAA), Eriosoma lanigerum (Hausmann) (Hemiptera: Aphididae) are reported. Annual surveys of H. calcarata presence and abundance in a Virginia, USA apple orchard revealed a bimodal distribution, with peaks in mid-June and mid-September. In the field, female H. calcarata oviposited on sentinel apple shoots infested with WAA, providing an efficient method for egg collection and larval production. Similarly, most field-collected females readily deposited viable eggs on WAA colonies in laboratory cages, demonstrating that mated females will oviposit in captivity. Survivorship of eggs and larvae transported to NZ was good, yielding adult flies in containment in Auckland. Adult, virgin female H. calcarata reared from eggs in captivity developed mature oocytes, providing an important step toward future mating studies in containment. Oviposition and larval feeding studies examined aspects of the intraguild interactions between H. calcarata and Aphelinus mali (Haldeman) (Hymenoptera: Aphelinidae), the sole biological control agent of WAA in NZ. Field tests using paired sentinel apple shoots with a non-parasitized or parasitized WAA colony revealed that although H. calcarata deposited eggs on both parasitized and non-parasitized colonies, fewest eggs were deposited on heavily parasitized colonies. Feeding studies showed that larval H. calcarata consumed fewer mummified aphids or aphids in an earlier stage of parasitization than non-parasitized aphids.

Assessing the non-target impacts of classical biological control agents: is host-testing always necessary?

Release of a biocontrol agent in New Zealand is typically preceded by non-target testing of native or valued species. Nevertheless, if both the target pest and the natural enemy are very different from any native fauna, then there may be no scientific justification for host testing. Gonatocerus ashmeadi (Girault) (Hymenoptera: Mymaridae) is being considered as a biocontrol agent for glassy winged sharpshooter, Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae), should the pest arrive. An assessment of the potential impact of G. ashmeadi on New Zealand’s Cicadellidae and Membracidae, from published literature data, indicates that none of these insects is at risk, as their eggs will not be recognised by the parasitoid because either their size or location places them outside the parasitoid’s search pattern. Consequently, there is no scientific case for any non-target host-testing to be carried out in containment.

Host range testing for risk assessment of a sexually dimorphic polyphagous invader, painted apple moth

A wide known host range in Australia and novel herbivory on native and naturalized species in New Zealand supported the decision to commence a NZ

Predicting the distribution of Gonatocerus ashmeadi, an egg parasitoid of glassy winged sharpshooter, in New Zealand

65 million eradication programme against painted apple moth [Teia anartoides (Walker) (Lepidoptera: Lymantriidae)] in Auckland (1999–2007). Laboratory no‐choice tests were designed to examine the ‘host’ status of the associations seen in the field. Laboratory tests investigated 79 native and introduced plant species with 122 provenances. Forty‐two percent of plants were capable of supporting larval development to adulthood, with male bias; 30% were defined as potential hosts with female larvae developed through to the pupal stage; > 10% survival indicated probable physiological hosts. Sporadic or more frequent attack of New Zealand native broom, and introduced lemon, apple, sycamore, walnut, cherry and poplar, was likely, with a wider range of hosts supporting male emergence. A few negative laboratory results contradicted field observations of significant damage by large numbers of larvae. The present study highlights the challenge faced with respect to predicting the ecological host range of invasive polyphagous species, whose biology is little known, during the early stages of a first invasion. The implications of a wider host range found in males than females are discussed.

Evaluation of the synthetic sex pheromone of the obscure mealybug, Pseudococcus viburni, as an attractant to conspecific males, and to females of the parasitoid Acerophagus maculipennis

The mymarid egg parasitoid Gonatocerus ashmeadi is a potential candidate for classical biological control of glassy winged sharpshooter (GWSS; Homalodisca vitripennis), should the pest arrive in New Zealand. However, the climate in the parasitoids native range in the southern USA is considerably warmer than that in New Zealand, which may pose an obstacle to establishment. Although G. ashmeadi is a very effective biocontrol agent in Florida, Hawaii and Western Polynesia, it appears currently to be limited by cooler climate in central and northern California – regions that typically have climates more similar to those in New Zealand. A CLIMEX model was used to predict the survival of G. ashmeadi in New Zealand by comparison with known parameters in the USA and western Pacific Islands. The model indicates that the establishment and distribution of G. ashmeadi is likely to be limited by the climate in New Zealand, although it will probably persist in warmer parts of the North Island. These predictions indicate that biocontrol of GWSS in New Zealand using G. ashmeadi will also require active management through varying regional integrated pest management programmes. Should GWSS arrive in New Zealand, G. ashmeadi should be selected from a population that has adapted to cooler parts of California. However, such a population is not known at present, so preventing GWSS from establishing in New Zealand remains a crucial strategy.