Brad Howlett - Academia.edu (original) (raw)

Papers by Brad Howlett

In New Zealand, unmanaged bees species can be important crop pollinators, but their abundance and... more In New Zealand, unmanaged bees species can be important crop pollinators, but their abundance and distribution is poorly known within hybrid carrot seed crops. Standardised counts of bees visiting flowering carrot umbels (1350 umbels observed/field) across 19 commercial hybrid fields were conducted between 1000 h and 1500 h. Despite honey bees being observed in all fields, abundance varied greatly between fields (mean=98.1; maximum=330, minimum=1). Other bees observed visiting umbels were Lasioglossum sordidum (17 fields; mean=14; maximum=65); Leioproctus sp. (12 fields; mean=2.0; maximum=19); Hylaeus sp. (one field; maximum= 1) and Bombus terrestris (six fields; mean=2.0; maximum=11). The number of individual bees (all species together) counted/ umbel on male fertile umbels was significantly higher than on male sterile umbels, a factor that could contribute to sub-optimal pollen flow between umbel lines by bees. Examination of their movements between male fertile and sterile lines is required to verify their efficiency as pollinators.

Varroa destructor is the most serious arthropod pest of honeybees (Meikle et al. 2012) destroying... more Varroa destructor is the most serious arthropod pest of honeybees (Meikle et al. 2012) destroying bee colonies not only in New Zealand, but worldwide (Donovan & Paul 2006). Apiarists currently rely heavily on synthetic acaricides (Meikle et al. 2012), however, resistance build up by varroa to these chemicals suggests their long term use is unsustainable (Meikle et al. 2012). The development of non chemical control techniques to control varroa populations within hives could provide a valuable and sustainable alternative to current management practices. Chelifers, also known as pseudoscorpions (Arachnida: Pseudoscorpionida) have shown potential as a biological control alternative for varroa management (Fagan et al. 2011). If chelifers prove to be successful at controlling varroa populations, the reliance on chemical control could be reduced (Donovan 2000). Chelifers are arachnids that have eight legs, a body up to about 8mm long and a pair of pincers projecting in front of them. Cheli...

Nature Communications, 2015

There is compelling evidence that more diverse ecosystems deliver greater benefits to people, and... more There is compelling evidence that more diverse ecosystems deliver greater benefits to people, and these ecosystem services have become a key argument for biodiversity conservation. However, it is unclear how much biodiversity is needed to deliver ecosystem services in a cost-effective way. Here we show that, while the contribution of wild bees to crop production is significant, service delivery is restricted to a limited subset of all known bee species. Across crops, years and biogeographical regions, crop-visiting wild bee communities are dominated by a small number of common species, and threatened species are rarely observed on crops. Dominant crop pollinators persist under agricultural expansion and many are easily enhanced by simple conservation measures, suggesting that cost-effective management strategies to promote crop pollination should target a different set of species than management strategies to promote threatened bees. Conserving the biological diversity of bees therefore requires more than just ecosystem-service-based arguments.

Baseline data on the distribution and abundance ofunmanaged pollinators and seed set in South Isl... more Baseline data on the distribution and abundance ofunmanaged pollinators and seed set in South Island white clover pasture have been gathered at locations where managed honey bees are scarce. The information is required to accurately predict the future impact of the Varroa mite on the South Island pastoral industry.

The Weta is the news bulletin of the Entomological Society of New Zealand. The Weta, like the soc... more The Weta is the news bulletin of the Entomological Society of New Zealand. The Weta, like the society's journal, the New Zealand Entomologist, promotes the study of the biology, ecology, taxonomy and control of insects and arachnids in an Australasian setting. The purpose of the news bulletin is to provide a medium for both amateur and professional entomologists to record observations, news, views and the results of smaller research projects.

Science (New York, N.Y.), Jan 29, 2013

The diversity and abundance of wild insect pollinators have declined in many agricultural landsca... more The diversity and abundance of wild insect pollinators have declined in many agricultural landscapes. Whether such declines reduce crop yields, or are mitigated by managed pollinators such as honey bees, is unclear. We found universally positive associations of fruit set with flower visitation by wild insects in 41 crop systems worldwide. In contrast, fruit set increased significantly with flower visitation by honey bees in only 14% of the systems surveyed. Overall, wild insects pollinated crops more effectively; an increase in wild insect visitation enhanced fruit set by twice as much as an equivalent increase in honey bee visitation. Visitation by wild insects and honey bees promoted fruit set independently, so pollination by managed honey bees supplemented, rather than substituted for, pollination by wild insects. Our results suggest that new practices for integrated management of both honey bees and diverse wild insect assemblages will enhance global crop yields.

New Zealand Entomologist, 2010

New Zealand Entomologist, 2010

Environmental changes in New Zealand over the last 200 years such as the intensifi cation of agri... more Environmental changes in New Zealand over the last 200 years such as the intensifi cation of agriculture have nearly eliminated some species of native bees from parts of their historic ranges. Consequently, the reproductive success of native plants reliant on native bees for pollination may be adversely impacted, thereby altering native ecosystems. The potential pollination rate of some introduced crops might also be reduced. Overwintering prepupae of the ground-nesting colletid bee Leioproctus huakiwi Donovan, 2007, were relocated in nests in soil and in artifi cial cells to new nest sites, where they established new populations which expanded by about 8-25 times over three years (and for the two sites together by 12.75 times), showing that large populations can develop rapidly. The two transference methods should be applicable to other species of colletids, indicating that relocation of these bees to new areas for both conservation and economic values is readily achievable.

Journal of Insect Science, 2013

The potential movement of transgenes from genetically modified crops to non-genetically modified ... more The potential movement of transgenes from genetically modified crops to non-genetically modified crops via insect-mediated pollen dispersal has been highlighted as one of the areas of greatest concern in regards to genetically modified crops. Pollen movement depends sensitively on spatial and temporal variation in the movement of insect pollinators between crop fields. This study tested the degree of variation in the diversity and relative abundance of flower-visiting insects entering versus leaving pak choi, Brassica rapa var. chinensis L. (Brassicales: Brassicaceae), crops throughout different stages of the flowering cycle. The relative abundance of flower-visiting insects varied significantly with Brassica crop phenology. Greater numbers of flower-visiting insects were captured inside rather than outside the crop fields, with the highest capture rates of flower-visitors coinciding with the peak of flowering in both spring-flowering and summer-flowering crops. Moreover, the ratio of flower-visiting insects entering versus leaving crop fields also varied considerably with changing crop phenology. Despite high variation in relative capture rates, the data strongly indicate non-random patterns of variation in insect movement in relation to crop phenology, with early-season aggregation of flower-visiting insects entering and remaining in the crop, and then mass emigration of flower-visiting insects leaving the crop late in the flowering season. Although pollen movement late in the flowering cycle might contribute relatively little to total seed set (and hence crop production), the findings here suggest that extensive late-season pollinator redistribution in the landscape could contribute disproportionately to long-distance gene movement between crops.

Journal of Insect Science, 2011

Onion, Allium cepa L. (Asparagales: Amaryllidaceae), crop fields grown for seed production requir... more 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.

Journal of Insect Behavior, 2005

Oviposition deterrence is common in many insects as an evolutionary mechanism to reduce subsequen... more Oviposition deterrence is common in many insects as an evolutionary mechanism to reduce subsequent larval competition. We investigated a suspected case of oviposition deterrence by the paropsine chrysomelid, Chrysophtharta bimaculata. In paired choice tests, gravid females were found to prefer ovipositing on host leaves without conspecific eggs, confirming the presence of an apparent oviposition deterrence mechanism. Washing egg batches in water, hexane or ethanol did not change this preference, suggesting that a soluble marking pheromone was not involved. Furthermore, it is unlikely that a plant derived oviposition deterring substance is produced as beetles showed no significant oviposition preference between leaves which had been oviposited upon, but then had the eggs removed, and those that had never been oviposited upon. In trials using artificial leaves and mimic egg batches, 'leaves' with 'egg batches' placed near the tip of the leaf (the preferred site of oviposition in this species) were significantly less likely to be laid upon than artificial leaves where mimic eggs were placed away from the tip. In combination, the results strongly infer that oviposition deterrence in C. bimaculata is due to the mechanical blocking of the oviposition site by the first laid eggbatch, rather than a specific oviposition deterring cue. The apparent oviposition deterrence in this insect may well be an outcome or evolutionary effect of oviposition-site selection, rather than a clear adaptive mechanism to decrease larval competition.

Journal of Applied Entomology, 2012

ABSTRACT Chelifers (Arachnida: Pseudoscorpionida), also known as pseudoscorpions, have been repor... more ABSTRACT Chelifers (Arachnida: Pseudoscorpionida), also known as pseudoscorpions, have been reported to be beneficial honeybee hive generalist pest predators for over 100 years and are occasionally noted by beekeepers in their hives. We collected chelifers within or closely associated with beehives in New Zealand. Under video observation conditions, they predated upon varroa mites while studiously ignoring bee larvae. Varroa mites reproduce at exponential rates during the spring season, and current chemical miticides rely on single treatments aiming for at least 90% control. An alternate strategy, removal of mites at a rate matching their reproductive capacity, although mathematically obvious, fails unless a suitable biological control agent is available. Our observations build on over 100 years of sporadic work to provide further evidence that chelifers show clear potential to be a suitable predator for varroa management in beehives. Approximately 25 chelifers can be expected to manage varroa populations in a single hive.

In New Zealand, unmanaged bees species can be important crop pollinators, but their abundance and... more In New Zealand, unmanaged bees species can be important crop pollinators, but their abundance and distribution is poorly known within hybrid carrot seed crops. Standardised counts of bees visiting flowering carrot umbels (1350 umbels observed/field) across 19 commercial hybrid fields were conducted between 1000 h and 1500 h. Despite honey bees being observed in all fields, abundance varied greatly between fields (mean=98.1; maximum=330, minimum=1). Other bees observed visiting umbels were Lasioglossum sordidum (17 fields; mean=14; maximum=65); Leioproctus sp. (12 fields; mean=2.0; maximum=19); Hylaeus sp. (one field; maximum= 1) and Bombus terrestris (six fields; mean=2.0; maximum=11). The number of individual bees (all species together) counted/ umbel on male fertile umbels was significantly higher than on male sterile umbels, a factor that could contribute to sub-optimal pollen flow between umbel lines by bees. Examination of their movements between male fertile and sterile lines is required to verify their efficiency as pollinators.

Varroa destructor is the most serious arthropod pest of honeybees (Meikle et al. 2012) destroying... more Varroa destructor is the most serious arthropod pest of honeybees (Meikle et al. 2012) destroying bee colonies not only in New Zealand, but worldwide (Donovan & Paul 2006). Apiarists currently rely heavily on synthetic acaricides (Meikle et al. 2012), however, resistance build up by varroa to these chemicals suggests their long term use is unsustainable (Meikle et al. 2012). The development of non chemical control techniques to control varroa populations within hives could provide a valuable and sustainable alternative to current management practices. Chelifers, also known as pseudoscorpions (Arachnida: Pseudoscorpionida) have shown potential as a biological control alternative for varroa management (Fagan et al. 2011). If chelifers prove to be successful at controlling varroa populations, the reliance on chemical control could be reduced (Donovan 2000). Chelifers are arachnids that have eight legs, a body up to about 8mm long and a pair of pincers projecting in front of them. Cheli...

Nature Communications, 2015

There is compelling evidence that more diverse ecosystems deliver greater benefits to people, and... more There is compelling evidence that more diverse ecosystems deliver greater benefits to people, and these ecosystem services have become a key argument for biodiversity conservation. However, it is unclear how much biodiversity is needed to deliver ecosystem services in a cost-effective way. Here we show that, while the contribution of wild bees to crop production is significant, service delivery is restricted to a limited subset of all known bee species. Across crops, years and biogeographical regions, crop-visiting wild bee communities are dominated by a small number of common species, and threatened species are rarely observed on crops. Dominant crop pollinators persist under agricultural expansion and many are easily enhanced by simple conservation measures, suggesting that cost-effective management strategies to promote crop pollination should target a different set of species than management strategies to promote threatened bees. Conserving the biological diversity of bees therefore requires more than just ecosystem-service-based arguments.

Baseline data on the distribution and abundance ofunmanaged pollinators and seed set in South Isl... more Baseline data on the distribution and abundance ofunmanaged pollinators and seed set in South Island white clover pasture have been gathered at locations where managed honey bees are scarce. The information is required to accurately predict the future impact of the Varroa mite on the South Island pastoral industry.

The Weta is the news bulletin of the Entomological Society of New Zealand. The Weta, like the soc... more The Weta is the news bulletin of the Entomological Society of New Zealand. The Weta, like the society's journal, the New Zealand Entomologist, promotes the study of the biology, ecology, taxonomy and control of insects and arachnids in an Australasian setting. The purpose of the news bulletin is to provide a medium for both amateur and professional entomologists to record observations, news, views and the results of smaller research projects.

Science (New York, N.Y.), Jan 29, 2013

The diversity and abundance of wild insect pollinators have declined in many agricultural landsca... more The diversity and abundance of wild insect pollinators have declined in many agricultural landscapes. Whether such declines reduce crop yields, or are mitigated by managed pollinators such as honey bees, is unclear. We found universally positive associations of fruit set with flower visitation by wild insects in 41 crop systems worldwide. In contrast, fruit set increased significantly with flower visitation by honey bees in only 14% of the systems surveyed. Overall, wild insects pollinated crops more effectively; an increase in wild insect visitation enhanced fruit set by twice as much as an equivalent increase in honey bee visitation. Visitation by wild insects and honey bees promoted fruit set independently, so pollination by managed honey bees supplemented, rather than substituted for, pollination by wild insects. Our results suggest that new practices for integrated management of both honey bees and diverse wild insect assemblages will enhance global crop yields.

New Zealand Entomologist, 2010

New Zealand Entomologist, 2010

Environmental changes in New Zealand over the last 200 years such as the intensifi cation of agri... more Environmental changes in New Zealand over the last 200 years such as the intensifi cation of agriculture have nearly eliminated some species of native bees from parts of their historic ranges. Consequently, the reproductive success of native plants reliant on native bees for pollination may be adversely impacted, thereby altering native ecosystems. The potential pollination rate of some introduced crops might also be reduced. Overwintering prepupae of the ground-nesting colletid bee Leioproctus huakiwi Donovan, 2007, were relocated in nests in soil and in artifi cial cells to new nest sites, where they established new populations which expanded by about 8-25 times over three years (and for the two sites together by 12.75 times), showing that large populations can develop rapidly. The two transference methods should be applicable to other species of colletids, indicating that relocation of these bees to new areas for both conservation and economic values is readily achievable.

Journal of Insect Science, 2013

The potential movement of transgenes from genetically modified crops to non-genetically modified ... more The potential movement of transgenes from genetically modified crops to non-genetically modified crops via insect-mediated pollen dispersal has been highlighted as one of the areas of greatest concern in regards to genetically modified crops. Pollen movement depends sensitively on spatial and temporal variation in the movement of insect pollinators between crop fields. This study tested the degree of variation in the diversity and relative abundance of flower-visiting insects entering versus leaving pak choi, Brassica rapa var. chinensis L. (Brassicales: Brassicaceae), crops throughout different stages of the flowering cycle. The relative abundance of flower-visiting insects varied significantly with Brassica crop phenology. Greater numbers of flower-visiting insects were captured inside rather than outside the crop fields, with the highest capture rates of flower-visitors coinciding with the peak of flowering in both spring-flowering and summer-flowering crops. Moreover, the ratio of flower-visiting insects entering versus leaving crop fields also varied considerably with changing crop phenology. Despite high variation in relative capture rates, the data strongly indicate non-random patterns of variation in insect movement in relation to crop phenology, with early-season aggregation of flower-visiting insects entering and remaining in the crop, and then mass emigration of flower-visiting insects leaving the crop late in the flowering season. Although pollen movement late in the flowering cycle might contribute relatively little to total seed set (and hence crop production), the findings here suggest that extensive late-season pollinator redistribution in the landscape could contribute disproportionately to long-distance gene movement between crops.

Journal of Insect Science, 2011

Onion, Allium cepa L. (Asparagales: Amaryllidaceae), crop fields grown for seed production requir... more 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.

Journal of Insect Behavior, 2005

Oviposition deterrence is common in many insects as an evolutionary mechanism to reduce subsequen... more Oviposition deterrence is common in many insects as an evolutionary mechanism to reduce subsequent larval competition. We investigated a suspected case of oviposition deterrence by the paropsine chrysomelid, Chrysophtharta bimaculata. In paired choice tests, gravid females were found to prefer ovipositing on host leaves without conspecific eggs, confirming the presence of an apparent oviposition deterrence mechanism. Washing egg batches in water, hexane or ethanol did not change this preference, suggesting that a soluble marking pheromone was not involved. Furthermore, it is unlikely that a plant derived oviposition deterring substance is produced as beetles showed no significant oviposition preference between leaves which had been oviposited upon, but then had the eggs removed, and those that had never been oviposited upon. In trials using artificial leaves and mimic egg batches, 'leaves' with 'egg batches' placed near the tip of the leaf (the preferred site of oviposition in this species) were significantly less likely to be laid upon than artificial leaves where mimic eggs were placed away from the tip. In combination, the results strongly infer that oviposition deterrence in C. bimaculata is due to the mechanical blocking of the oviposition site by the first laid eggbatch, rather than a specific oviposition deterring cue. The apparent oviposition deterrence in this insect may well be an outcome or evolutionary effect of oviposition-site selection, rather than a clear adaptive mechanism to decrease larval competition.

Journal of Applied Entomology, 2012

ABSTRACT Chelifers (Arachnida: Pseudoscorpionida), also known as pseudoscorpions, have been repor... more ABSTRACT Chelifers (Arachnida: Pseudoscorpionida), also known as pseudoscorpions, have been reported to be beneficial honeybee hive generalist pest predators for over 100 years and are occasionally noted by beekeepers in their hives. We collected chelifers within or closely associated with beehives in New Zealand. Under video observation conditions, they predated upon varroa mites while studiously ignoring bee larvae. Varroa mites reproduce at exponential rates during the spring season, and current chemical miticides rely on single treatments aiming for at least 90% control. An alternate strategy, removal of mites at a rate matching their reproductive capacity, although mathematically obvious, fails unless a suitable biological control agent is available. Our observations build on over 100 years of sporadic work to provide further evidence that chelifers show clear potential to be a suitable predator for varroa management in beehives. Approximately 25 chelifers can be expected to manage varroa populations in a single hive.