P.L. Lo

Abundance of leafrollers and their parasitoids on selected host plants in New Zealand

Abstract The comparative abundance of orchard pest leafroller larvae was determined on eight host plants in the vicinity of pipfruit orchards. The greatest numbers occurred in Canterbury, followed by Nelson, Hawkes Bay, and Central Otago. In Hawkes Bay, leafroller larvae were Ctenopseustis obliquana (41%), Planotortrix octo (15%), Epiphyas postvittana (16%), and Cnephasia jactatana (9%), and were most abundant on poplar, willow, and alder. In Nelson, leafrollers were E. postvittana (25%), Planotortrix excessana (23%), C. obliquana (23%), and C. herana (22%), found on willow, alder, clover, poplar, gorse, broom, dock, and plantain. In Canterbury, larvae were C. herana (51%), E. postvittana (34%), and P. octo (15%), mainly on broom, gorse, alder, poplar, dock, and clover. Leafrollers were very rare on host plants sampled in Central Otago, despite their pest status in horticulture. A total of 1460 larvae were reared to adults from the four regions, with 31% parasitism, of which two thirds were Dolichogenid...

Trapping Dasinuera mali (Diptera: Cecidomyiidae) in Apples

Abstract The midgeDasineura mali (Kieffer) (Diptera: Cecidomyiidae) is a significant pest of apples (Malus spp.), and the recent identification of the female sex pheromone is enabling new direct control tactics to be considered. Direct control using male suppression will require knowledge of the frequency of multiple mating, dispersal and colonization rates, and the efficiency of male removal. Males were able to mate up to five times, with a mean of 2.7 times when presented in a 10 female-to-1 male group, designed to simulate male suppression. Male catch in response to the pheromone loading was curvilinear over 4 orders of magnitude from 3 μg to 30 mg on rubber septa. Trapping using a high-dose pheromone lure was combined with oil-based traps similar to the inexpensive New Zealand “Lynfield trap” used for tephritid surveillance, to test male suppression in young orchard blocks at 500 traps per ha. Monitoring traps indicated 96% lower catch in the treated plots compared with control plots, over 137 d. However, a lack of shoot tip infestation in both treated and untreated plots indicated limited colonization and prevented an assessment of potential population suppression. Furthermore, a contribution to these results from communication disruption cannot be ruled out. Replicated transects of frequency of infested shoots from a mature orchard across the adjacent young block confirmed that colonization by ovipositing females was essentially limited to the first 30 m.

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.

Factors affecting feeding site preferences of lightbrown apple moth, Epiphyas postvittana (Lepidoptera: Tortricidae), on apple trees in New Zealand.

Abstract The infestation of apple (Malus domestica) trees by Epiphyas postvittana (Walker) larvae was studied over 3 years. Fresh damage to leaves increased progressively during the season, although in Nelson it declined in April. Fruit damage was first detected in December and increased throughout the season. The incidence of fruit damage was most strongly correlated with the surface area of fruit. Single leaves were the preferred feeding site for larvae on terminal shoots, although when whole branches were examined, most shelters occurred between two leaves. Feeding sites on fruit predominantly involved contact with a leaf or another apple. A field experiment examined the influence of physical contact and fruit maturation on leafroller damage. E. postvittana larvae were offered a choice of feeding sites involving leaves and three types of “apple” namely untreated apples, apples treated with chlorethephon to promote ripening, and plastic balls. There was 16% more damage on treated compared with untreated fruit, but similar levels of damage to leaves touching the three types of apple. Although riper fruit were more attractive to E. postvittana larvae, their preference for physical contact had a greater influence on the selection of feeding sites. The increase in fruit damage over time was mainly due to the increasing extent of contact between leaves and other fruit as the apples enlarged.

Spatial analysis of mass trapping: how close is close enough?

BACKGROUND The identification of new attractants can present opportunities for developing mass trapping, but standard screening methods are needed to expedite this. We have developed a simple approach based on quantifying trap interference in 4 × 4 trap arrays with different spacings. We discuss results from sex pheromones in Lepidoptera (light brown apple moth, Epiphyas postvittana), Diptera (apple leaf curling midge, Dasineura mali) and Homoptera (citrophilous mealybug, Pseudococcus calceolariae), compared with a kairomone for New Zealand flower thrips (Thrips obscuratus). RESULTS The ratio of catch in corner traps to catch in centre traps was 25:1 at 750 D. mali traps ha(-1) , and was still ∼5:1 at 16 traps ha(-1) , suggesting trap interference even at such low trap densities. Trap competition for sex pheromone lures at close spacing (<5 m) was evident in 16-trap arrays of P. calceolariae, but less so for E. postvittana. No trap competition was observed at 4 m spacings with the kairomone for T. obscuratus. CONCLUSIONS The ratio of catch in traps in the corner and centre of a 16-trap array at different spacings offers a rapid preliminary assessment method for determining the potential for mass trapping. Additional knowledge of vital rates and dispersal is needed for predicting population suppression. Our approach should have value in mass trapping development.

Spatial analysis of mass trapping

BACKGROUND The identification of new attractants can present opportunities for developing mass trapping, but standard screening methods are needed to expedite this. We have developed a simple approach based on quantifying trap interference in 4 × 4 trap arrays with different spacings. We discuss results from sex pheromones in Lepidoptera (light brown apple moth, Epiphyas postvittana), Diptera (apple leaf curling midge, Dasineura mali) and Homoptera (citrophilous mealybug, Pseudococcus calceolariae), compared with a kairomone for New Zealand flower thrips (Thrips obscuratus). RESULTS The ratio of catch in corner traps to catch in centre traps was 25:1 at 750 D. mali traps ha(-1) , and was still ∼5:1 at 16 traps ha(-1) , suggesting trap interference even at such low trap densities. Trap competition for sex pheromone lures at close spacing (<5 m) was evident in 16-trap arrays of P. calceolariae, but less so for E. postvittana. No trap competition was observed at 4 m spacings with the kairomone for T. obscuratus. CONCLUSIONS The ratio of catch in traps in the corner and centre of a 16-trap array at different spacings offers a rapid preliminary assessment method for determining the potential for mass trapping. Additional knowledge of vital rates and dispersal is needed for predicting population suppression. Our approach should have value in mass trapping development.

N-Butyl Sulfide as an Attractant and Coattractant for Male and Female Codling Moth (Lepidoptera: Tortricidae)

ABSTRACT Research to discover and develop attractants for the codling moth, Cydia pomonella L., has involved identification of the chemicals eliciting moth orientation to conspecific female moths, host fruits, fermented baits, and species of microbes. Pear ester, acetic acid, and N-butyl sulfide are among those chemicals reported to attract or enhance attractiveness to codling moth. We evaluated the trapping of codling moth with N-butyl sulfide alone and in combination with acetic acid and pear ester in apple orchards. Acetic acid was attractive in two tests and N-butyl sulfide was attractive in one of two tests. N-Butyl sulfide increased catches of codling moth when used with acetic acid to bait traps. N-Butyl sulfide also increased catches of codling moth when added to traps baited with the combination of acetic acid and pear ester. Male and female codling moth both responded to these chemicals and chemical combinations. These results provide a new three-component lure comprising N-butyl sulfide, acetic acid, and pear ester that is stronger for luring codling moth females than other attractants tested.

Prospects for the control of apple leaf midge Dasineura mali (Diptera: Cecidomyiidae) by mass trapping with pheromone lures.

BACKGROUND Apple leaf midge, Dasineura mali (Kieffer), poses quarantine issues for some apple export markets because larvae occasionally pupate in the stem end and calyx of fruit. Pheromone-baited oil-filled containers were used in 1 ha orchard plots to trap adult male D. mali in order to test the potential for mass trapping to reduce populations. RESULTS Mass-trapped plots had 97% fewer adult males in pheromone traps and 48% fewer larvae per shoot in the second D. mali generation compared with untreated areas. Oil traps caught on average 900 000 D. mali per plot over 11 weeks during the second and third generations. Catches averaged 9200 per trap at plot corners. By comparison, catches were 51% lower 10-25 m away along borders, 80% lower at the midpoint of borders and 95% lower >7 m from plot edges. Fruit infestation was low (four out of 8000 apples). CONCLUSION The attractiveness of the pheromone, monophagous habit and low mobility of D. mali enhance the prospects for successful mass trapping. Countering this are high populations, multivoltinism and aspects of mating behaviour. Mass trapping would probably have been more effective had it been in place season long and conducted over successive years. It needs refinements and more study before becoming a feasible control option for D. mali.

Reduction in leafroller (Lepidoptera: Tortricidae) abundance in orchards and vineyards 1976-2016, in Hawke's Bay, New Zealand: Leafroller abundance on orchards and vineyards

Three leafroller species were monitored between 1976 and 2016 by bait and pheromone trapping for adults, larval damage to apples and timed searches on various hosts. Populations of all three species decreased substantially; however, the endemic Planotortrix octo and Ctenopseustis obliquana declined to a much greater extent than did the introduced Epiphyas postvittana. The two endemic species dominated in the 1970s, whereas they are now rarely found on fruit crops. Epiphyas postvittana has now become the principal leafroller species. Leafrollers damaged over 20% of apples receiving no insecticides during the 1980s but, subsequent to 2000, damage has been below 2%. Between 1994–1999 and 2008–2011, the numbers of immature leafrollers in searches on fruit crop and noncrop hosts decreased by 55%. We attribute reduced leafroller populations to increased biological control and changes to insecticide programmes. Several parasitoids were introduced around 1980 and parasitism increased by 19% between 1994–1999 and 2008–2011. Replacing broad‐spectrum insecticides with selective insecticides in the mid‐1990s likely enhanced this trend. Leafrollers were formerly major pests, whereas their status has now changed to being minor pests. Today, they are uncommon on managed and unmanaged fruit crops and noncrop host plants on orchards and vineyards in Hawkes Bay.