A review of the scientific literature identified the need to examine sub-lethal
behavioural effects of a
range of insecticides on one of the most important and
widely used groups of arthropods in biological control, the ladybirds (Chapter 1).
The aphidophagous seven-spotted ladybird, Coccinellci septempunctata was
identified as being an ideal model. Culture methods were developed from existing
protocols for both the predator and two species of prey, Acyrthosiphon pisum and
Myzus persicae, before using pesticide usage survey reports to identify insecticides
that would provide the study with the broadest relevance to agriculturists (Chapter 2).
Safe and effective spraying protocols were established using equipment which was
assessed for its effectiveness and evenness of spray deposition (Chapter 2).
The locomotory behavioural responses of C. septempunctata to the insecticides and
their active ingredients were examined in experimental, controlled environment
arenas using video analysis software (Chapter 3). Experimental blocking enabled the
behavioural responses to a variety of spray conditions to be directly compared,
revealing a graded and consistent response to the insecticide residues. The
pirimicarb-based insecticide, Aphox™, had the least effect on both locomotor
behaviour and mortality, such that no significant differences between this treatment
and water controls were recorded in either respect. The X-cyhalothrin-based
insecticide, Hallmark with Zeon Technology™, had the greatest effect on locomotor
behaviour, causing the coccinellids to reduce their overall movement over the three
hours of the tests but the effect on mortality was minimal. The second pyrethroid
tested, the cypermethrin-based Toppel 10™, drew similar responses from C.
septempunctata that were only marginally less pronounced than those of Hallmark.
The organophosphate insecticides, the chlorpyrifos-based Dursban 75WG™ and the
dimethoate based BASF Dimethoate 40™, had limited but significant effects on
aspects of the coccinellids' locomotor behaviour and caused significant mortality.
Behaviour and survival patterns observed at the lower application rate tested were
similar to those from the full-rate tests. Experiments were carried out to investigate
behavioural responses to the active ingredients and carrier formulations in isolation.
Responses to the insecticides' active ingredients demonstrated that in most cases, the
carrier formulation was responsible for the locomotor patterns observed with the
products. Although in some cases the opposite was true and the active ingredients
elicited responses where the entire products did not, suggesting that the carrier
formulation may have inhibited the expression of a response to the active ingredient
when testing the entire product. Additionally, C. septempunctata did not demonstrate
a preference for treated or untreated substrates, regardless of the treatment applied.
C. septempunctata did not demonstrate preferences for treated or untreated prey
when M. persicae were sprayed with insecticides and the coccinellids' consumption
rates were recorded (Chapter 4). In these experiments, the pyrethroids again drew the
greatest response from C. septempunctata, reducing consumption by the largest
amount, whereas the organophosphates led to the greatest mortality. The consistency
with the results from Chapter 3 was further reinforced in Chapter 4 by the absence of
a response to Aphox-treated prey. Spectrophotometric experiments were conducted
using coloured dye to investigate the evenness of spray distribution and deposition
provided by the equipment used in Chapter 4. These experiments also enabled the
amount of spray collected by each aphid to be quantified.
To investigate how insecticides are detected in C. septempunctata, scanning electron
microscopy (SEM) was used to conduct a morphological study of the palpi and tarsi
(Chapter 5). This was followed by an electrophysiological study on the maxillary
palps and a study of the coccinellids responses to olfactory stimuli from the
insecticides (Chapters 5, 6). The SEM study identified a hitherto unrecorded type of
sensilla on the labial palps and biometric analysis extended the level of sexual
dimorphism known for this species. Importantly for this study, no chemosensilla
were found on the tarsi and with three times more chemosensilla than any other sense
organ, the most likely organ responsible for insecticide detection in C.
septempunctata was the maxillary palps. The maxillary palps are thought to be
involved principally in contact chemoreception, and detection of Dimethoate was
confirmed using electrophysiological techniques. The positive neurological response
to both the product and the blank formulation (Chapter 5), coupled with the absence
of a behavioural response to the insecticide odours (Chapter 6) and the presence of
behavioural responses to treated substrates (Chapters 3, 6), provide further evidence
that contact chemoreception plays a major role in insecticide detection in C.