Assessing the effect of plant surface on the predatory ability of Orius vicinus : a potential biological control agent of the tomato-potato psyllid (Bactericera cockerelli) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Zoology at Massey University, Palmerston North, New Zealand
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Date
2019
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Massey University
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Abstract
The tomato-potato psyllid (TPP), Bactericera cockerelli (Sulc), is a pest to solanaceous
crops (e.g. potato, tomato, peppers, and eggplant) and is associated with economically
important plant diseases. Subsequently, chemical control is the preferred management
option. However, chemical reliance is associated with a host of issues. The development
of biological control methods is vital to implementing Integrated Pest Management
(IPM) programs as an alternative to broad-spectrum insecticide usage. The predatory
bug Orius vicinus (Ribaut) is a potential biological control agent that is capable of
consuming all nymphal life stages of TPP.
In order to be a commercially viable management option, potential biological control
agents of TPP have to cope with the different morphological plant features of the pest’s
wide range of host plants. Tomato and capsicum plant surfaces were selected as the
experimental surfaces for my thesis because they differ significantly in their substrate
morphology. Tomato plant surfaces can be a hostile environment for potential
biological control agents due to the negative effect tomato trichomes have on their
foraging performance. Alternatively, because capsicum plant surfaces are virtually void
of trichomes they appear to be more suitable for effective biological control agent
deployment.
I exposed the predatory bug to a variety of TPP nymph densities (10, 20, 30 and 40
individuals) in order to determine the functional response of O. vicinus. Furthermore,
the predatory bug was exposed to all five TPP nymphal stages simultaneously. The
predatory performance of O. vicinus was also assessed on experimental arenas varying
in complexity (leaflet vs. small plant environments). The functional response was
determined to be Type II on both plant surfaces. Nymph consumption at higher prey
densities (30 and 40 nymphs) was significantly greater on capsicum than on tomato.
Nymph consumption at lower prey densities (10 and 20 nymphs) was only significantly
greater on capsicum when the complexity of the experimental arena increased from
leaflet to small plant. The influence of O. vicinus in nymph dispersal was also assessed.
My results revealed that the presence of O. vicinus increased the dispersal of nymphs to
lower leaf surfaces and that nymph dispersal was significantly greater on capsicum than
on tomato.
TPP nymph size preference by O. vicinus was determined in my study. I established that
the predatory bug is capable of killing all nymphal stages. My study strongly indicated
that the predatory bug is more likely to target and consume medium (3rd instars) and
large nymphs (4th and 5th instars) over small nymphs (1st and 2nd instars). I investigated
the behaviour of O. vicinus adults and TPP nymphs during their interactions via video
recordings. The predatory bug spent a significantly greater amount of time investigating
TPP nymphs on capsicum than on tomato. There was significantly higher number of
attacks recorded on capsicum. The greater killing percentage on tomato suggests that
the defensive capabilities of TPP nymphs appear to have been negatively affected by the
tomato substrate.
The results from my study indicate that augmentative releases of O. vicinus, in the
presence of smaller TPP nymphs, could be a viable biological control option on
capsicum plants. However, the predatory bug will likely struggle if deployed on tomato
plants. Future studies should be conducted in settings such as open field or glasshouses
using multiple predatory bugs in the presence of susceptible life stages to assess
augmentative release efficiency.
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Keywords
Anthocoridae, Behavior, Paratrioza cockerelli, Biological control, Plant surfaces, Tomatoes, Peppers, Morphology, tomato-potato psyllid (TPP), Bactericera cockerelli, Orius vicinus, functional response, prey preference, plant surface morphology, capsicum, tomato