Native aphids of New Zealand--diversity and host associations

At least 15 species of aphids are now recognised as New Zealand natives and most of these are very likely to be endemic. Most native aphids belong in the subfamily Aphidinae (Aphidini), with a possible single species in Aphidinae-Macrosiphini, at least two in Neophyllaphidinae and one in Taiwanaphidinae. With one exception, native aphids are restricted to a single host plant genus, and these hosts are from 13 genera and 12 plant families in the Pinales and Angiospermae-Eudicotyledonae, suggesting that the aphids are a remnant fauna. No known native aphids have host plants from the Pteridophyta or Angiospermae-Monocotyledonae, with the possible exception of two possibly native species extracted from native tussock grassland turfs. Most host plant genera have some degree of Gondwanan distribution, but only two indigenous species are found on large forest trees and only one host is deciduous. Native aphids have been recorded from sea level to the subalpine zone, reflecting their host plant distributions. Sexual reproduction, followed by several parthenogenetic generations on the same host plant, appears to be the norm for most species. Eggs appear to be used for surviving winter conditions in some species and summer conditions in others. Native aphid distribution and abundance varies with five species considered to be scarce, one species localised, two species sparse and three relatively common based on current knowledge.

Estimating development rate and thermal requirements of Bactericera cockerelli (Hemiptera: Triozidae) reared on potato and tomato by using linear and nonlinear models

The temperature-dependent development of tomato psyllid (also called potato psyllid), Bactericera cockerelli (Sulc), was studied in the laboratory at seven constant temperatures (8, 10, 15, 20, 23, 27, and 31°C), 50-60% RH, and a photoperiod of 16:8 (L:D) h on leaves of whole potato (Solanum tuberosum L.) and tomato (Solanum lycopersicum L.) plants. Developmental time in days for immature stages and total development (egg to adult) on both host species were inversely proportional to temperature between 8 and 27°C but increased at 31°C. One linear and two nonlinear models were fitted to the data. The lower developmental thresholds, calculated using the linear model for egg, total nymph, and total development (from oviposition to adult emergence) were 7.9, 4.2, and 7.1°C (reared on potato) and 7.2, 5.3, and 7.5°C (reared on tomato), respectively. The thermal constant (K) for total development was 358 (reared on potato), and 368 (reared on tomato) degree-days (DD). Two nonlinear models, Briere and Lactin, fit the data well as measured by goodness-of-fit criteria, the residual sum of square (RSS) and Akaike information criterion (AIC). Temperature threshold parameters for these nonlinear models (T(0), T(opt), and T(max)) were estimated for eggs, total nymphal stages, and total development time (egg to adult). The Briere model is highly recommended for the description of temperature-dependent development of tomato psyllid. Results from this study will provide basic information on the biology of tomato psyllid and have potential for the development of predictive models of the seasonal progress of this invasive pest.

The diversity and abundance of small arthropods in onion, Allium cepa, seed crops, and their potential role in pollination

Onion, Allium cepa L. (Asparagales: Amaryllidaceae), crop fields grown for seed production require arthropod pollination for adequate seed yield. Although many arthropod species visit A. cepa flowers, for most there is little information on their role as pollinators. Small flower visiting arthropods (body width < 3 mm) in particular are rarely assessed. A survey of eight flowering commercial A. cepa seed fields in the North and South Islands of New Zealand using window traps revealed that small arthropods were highly abundant among all except one field. Insects belonging to the orders Diptera and Thysanoptera were the most abundant and Hymenoptera, Collembola, Psocoptera, Hemiptera, and Coleoptera were also present. To test whether small arthropods might contribute to pollination, seed sets from umbels caged within 3 mm diameter mesh cages were compared with similarly caged, hand-pollinated umbels and uncaged umbels. Caged umbels that were not hand-pollinated set significantly fewer seeds (average eight seeds/umbel, n = 10) than caged hand-pollinated umbels (average 146 seeds/umbel) and uncaged umbels (average 481 seeds/umbel). Moreover, sticky traps placed on umbels within cages captured similar numbers of small arthropods as sticky traps placed on uncaged umbels, suggesting cages did not inhibit the movement of small arthropods to umbels. Therefore, despite the high abundance of small arthropods within fields, evidence to support their role as significant pollinators of commercial A. cepa seed crops was not found.

Comparison of life history parameters of two Frankliniella occidentalis (Thysanoptera: Thripidae) strains in New Zealand

Two strains of western flower thrips, Frankliniella occidentalis (Pergande), are reputedly found in New Zealand. One strain was recorded in 1934, and it is most common in flowers of Lupinus arboreus outdoors (lupin strain); the other strain was first recorded in New Zealand in 1992 and is found mostly indoors on greenhouse crops (greenhouse strain). Laboratory studies were conducted to compare the life history parameters of these two strains. Thrips from each strain were fed sucrose solution and capsicum or lupin pollen and reared at 25 degrees C, >60% RH, and 16 L:8 D photoperiod. Significant differences in life history parameters were found. Preoviposition time was significantly shorter, and oviposition rate and fecundity were markedly higher (four-fold) for the greenhouse than for the lupin strain. The lupin strain performed significantly better on the capsicum pollen, laying more than twice as many eggs than on the lupin pollen over a 14-d period. The greenhouse strain development time from larvae to adult was marginally faster (0.7-1.1 d less) than the lupin strain because of a shorter prepupal and a marginally shorter pupal development time. Females of the greenhouse strain lived on average 69% longer than females from the lupin strain. Large differences in the intrinsic growth rate (r(m)) were found, with r(m) being 1.4-1.8 times higher for the greenhouse strain than the lupin strain, depending on pollen source. The results are discussed in relation to different ecological requirements and pest status of the two strains.

Pyridine compounds increase thrips (Thysanoptera: Thripidae) trap capture in an onion crop

The effect of the thrips (Thysanoptera: Thripidae) lures ethyl isonicotinate, methyl isonicotinate, and ethyl nicotinate on numbers of thrips captured in white water traps in an onion (Allium spp.) crop, in New Zealand, was examined. Female onion thrips, Thrips tabaci Lindeman (69.0%), and Thrips obscuratus Crawford (27.8%) (males and females) were the most common species found in traps in the onion crop. Ethyl isonicotinate, methyl isonicotinate, and ethyl nicotinate caught 18, 12, and 4x more onion thrips, respectively, than controls (no-lure). In contrast, traps with ethyl isonicotinate set up in a grass field at the same time as the onion crop trial caught 84x more onion thrips than traps without this lure. For T. obscuratus, traps with ethyl isonicotinate, methyl isonicotinate, and ethyl nicotinate caught 10, 13, and 12x more thrips, respectively, than controls in the onion crop.