Investigations Of The Biology Of The Pest Aphid Aulacorthum Solani (Kaltenbach) (Hemiptera: Aphididae) And Of Biological Control Agents For Control Of Multi-Species Aphid Outbreaks In Greenhouse Floriculture Crops.

Foxglove aphid, Aulacorthum solani (Kaltenbach), has recently become a significant pest of greenhouse crops in the north eastern U.S., Canada, and the U.K. Given its previous status as an occasional pest, little was known about its biology or ecology. Using a North American population, development time and life table statistics of A. solani were investigated at 6 temperatures. Aulacorthum solani developed fastest (6.9 ± 0.29 d) and had the highest intrinsic rate of increase (rm = 0.25) at 25 °C; limited development was seen at higher temperatures (rm = -0.24 at 30 °C). A study of 10 different greenhouse crops showed that these aphids generally distribute to bottom leaves of vegetative plants, but move upwards when plants are reproductive. Biological control of A. solani using the generalist aphid predator Aphidoletes aphidimyza (Rondani) was assessed in a series of greenhouse experiments. Here, the green peach aphid, Myzus persicae (Sulzer), was also included because aphid pests can co-occur. Experiments showed that A. aphidimyza perceives aphid colonies located on new growth of plants (meristems or top leaves) to be of higher value as oviposition sites compared to other plant locations. Aulacorthum solani-infested plants, with aphids primarily present on lower leaves or flowers, received fewer eggs than M. persicae-infested plants. In trials using a single innundative release of the predator, this translated to more variable control of A. solani compared to M. persicae (12-80% vs. 78-95%, respectively; tested across several stages of plant growth). This is likely partially attributable to apparent competition, since control of A. solani was significantly improved in the absence of alternate prey. Entomopathogenic fungi were assessed as another biocontrol option against aphids, including the melon aphid, Aphis gossypii Glover. Novel isolates of fungi originally collected from aphid hosts were sought to potentially increase pathogenicity. However, no isolate tested, commercial or novel, resulted in acceptable mortality of 1st instar aphid nymphs, with all LC50 values >700 conidia/mm2 under ideal lab conditions. Control options for A. solani and multi-species aphid infestations are discussed in light of the results presented in this thesis

Biological Control Outcomes Using the Generalist Aphid Predator Aphidoletes aphidimyza under Multi-Prey Conditions

The aphidophagous midge Aphidoletes aphidimyza (Diptera: Cecidomyiidae) is used in biological control programs against aphids in many crops. Short-term trials with this natural enemy demonstrated that that females prefer to oviposit among aphids colonizing the new growth of plants, leading to differential attack rates for aphid species that differ in their within-plant distributions. Thus, we hypothesized that biological control efficacy could be compromised when more than one aphid species is present. We further hypothesized that control outcomes may be different at different crop stages if aphid species shift their preferred feeding locations. Here, we used greenhouse trials to determine biological control outcomes using A. aphidimyza under multi-prey conditions and at different crop stages. At all plant stages, aphid species had a significant effect on the number of predator eggs laid. More eggs were found on M. persicae versus A. solani-infested plants, since M. persicae consistently colonized plant meristems across plant growth stages. This translated to higher numbers of predatory larvae on M. periscae-infested plants in two out of our three experiments, and more consistent control of this pest (78%–95% control across all stages of plant growth). In contrast, control of A. solani was inconsistent in the presence of M. persicae, with 36%–80% control achieved. An additional experiment demonstrated control of A. solani by A. aphidimyza was significantly greater in the absence of M. persicae than in its presence. Our study illustrates that suitability of a natural enemy for pest control may change over a crop cycle as the position of prey on the plant changes, and that prey preference based on within-plant prey location can negatively influence biological control programs in systems with pest complexes. Careful monitoring of the less-preferred pest and its relative position on the plant is suggested

Ecological Interactions Affecting the Efficacy of Aphidius colemani in Greenhouse Crops

Aphidius colemani Viereck (Hymenoptera: Braconidae) is a solitary endoparasitoid used for biological control of many economically important pest aphids. Given its widespread use, a vast array of literature on this natural enemy exists. Though often highly effective for aphid suppression, the literature reveals that A. colemani efficacy within greenhouse production systems can be reduced by many stressors, both biotic (plants, aphid hosts, other natural enemies) and abiotic (climate and lighting). For example, effects from 3rd and 4th trophic levels (fungal-based control products, hyperparasitoids) can suddenly decimate A. colemani populations. But, the most chronic negative effects (reduced parasitoid foraging efficiency, fitness) seem to be from stressors at the first trophic level. Negative effects from the 1st trophic level are difficult to mediate since growers are usually constrained to particular plant varieties due to market demands. Major research gaps identified by our review include determining how plants, aphid hosts, and A. colemani interact to affect the net aphid population, and how production conditions such as temperature, humidity and lighting affect both the population growth rate of A. colemani and its target pest. Decades of research have made A. colemani an essential part of biological control programs in greenhouse crops. Future gains in A. colemani efficacy and aphid biological control will require an interdisciplinary, systems approach that considers plant production and climate effects at all trophic levels

First records of invasive agricultural pests Thrips parvispinus (Karny, 1922) and Thrips setosus Moulton, 1928 (Thysanoptera: Thripidae) in Canada

Horticultural imports between countries can result in novel introductions of non-native insect species which reside on these plants, particularly in greenhouse scenarios. Here, we document the first Canadian records of Thrips parvispinus Karny, 1922 and Thrips setosus Moulton, 1928 (Thysanoptera: Thripidae) in southern Ontario greenhouses on Mandevilla Lindley (Apocynaceae) and Hydrangea Linnaeus (Hydrangeaceae), respectively. These species can reduce agricultural yields and cause economic losses from extensive feeding damage on a wide range of fruit and vegetable crops, as well as ornamental plants. While native to Asia, both species have spread throughout Europe and have recently been detected in the United States of America. Morphological identification of the Canadian records was confirmed by sequencing the DNA barcode region of the mitochondrial gene cytochrome c oxidase subunit I (CO1). Analysis of all publicly available CO1 haplotypes for both species indicate that the Canadian records are identical to those previously reported form Indonesia and Belgium. To assist in the identification of T. parvispinus and T. setosus, we characterize the adult sexes and distinguish these from similar species

Biological Control Outcomes Using the Generalist Aphid Predator Aphidoletes aphidimyza under Multi-Prey Conditions

The aphidophagous midge Aphidoletes aphidimyza (Diptera: Cecidomyiidae) is used in biological control programs against aphids in many crops. Short-term trials with this natural enemy demonstrated that that females prefer to oviposit among aphids colonizing the new growth of plants, leading to differential attack rates for aphid species that differ in their within-plant distributions. Thus, we hypothesized that biological control efficacy could be compromised when more than one aphid species is present. We further hypothesized that control outcomes may be different at different crop stages if aphid species shift their preferred feeding locations. Here, we used greenhouse trials to determine biological control outcomes using A. aphidimyza under multi-prey conditions and at different crop stages. At all plant stages, aphid species had a significant effect on the number of predator eggs laid. More eggs were found on M. persicae versus A. solani-infested plants, since M. persicae consistently colonized plant meristems across plant growth stages. This translated to higher numbers of predatory larvae on M. periscae-infested plants in two out of our three experiments, and more consistent control of this pest (78%–95% control across all stages of plant growth). In contrast, control of A. solani was inconsistent in the presence of M. persicae, with 36%–80% control achieved. An additional experiment demonstrated control of A. solani by A. aphidimyza was significantly greater in the absence of M. persicae than in its presence. Our study illustrates that suitability of a natural enemy for pest control may change over a crop cycle as the position of prey on the plant changes, and that prey preference based on within-plant prey location can negatively influence biological control programs in systems with pest complexes. Careful monitoring of the less-preferred pest and its relative position on the plant is suggested