A comprehensive phylogeny helps clarify the evolutionary history of host breadth and lure response in the Australian Dacini fruit flies (Diptera: Tephritidae).

The tribe Dacini (Diptera: Tephritidae) contains over 930 recognised species and has been widely studied due to the economic importance of some taxa, such as the Oriental fruit fly Bactrocera dorsalis. Despite the attention this group has received, very few phylogenetic reconstructions have comprehensively sampled taxa from a single biogeographic region, thereby limiting our capacity to address more targeted evolutionary questions. To study the evolution of diet breadth and male lure response, two key traits fundamental to understanding dacine diversity and the biology of pest taxa, we analysed 273 individuals representing 144 described species from Australia (80% continental coverage), the Pacific, and select close relatives from South-east Asia to estimate a dated molecular phylogenetic reconstruction of the Dacini. We utilised seven loci with a combined total of 4,332 nucleotides, to estimate both Bayesian and Maximum Likelihood phylogenies of the tribe. Consistent with other molecular phylogenies of the tribe, there was a high level of disagreement between the placement of species in the phylogeny and their current subgeneric and species-complex level taxonomies. The Australian fauna exhibit high levels of endemism, with radiations of both exclusively Australian clades, and clades that originate elsewhere (e.g. the Bactrocera dorsalis species group). Bidirectional movement of species has occurred between Papua New Guinea and Australia, with evidence for multiple incursions over evolutionary time. The Bactrocera aglaiae species group emerged sister to all other Bactrocera species examined. Divergence time estimates were âˆ¼ 30 my younger than previously reported for this group, with the tribe diverging from its most recent common ancestor âˆ¼ 43 mya. Ancestral trait reconstruction and tests for trait phylogenetic signal revealed a strong signal for the evolution of male lure response across the tree, with cue-lure/raspberry ketone lure response the ancestral trait. Methyl eugenol response has arisen on multiple, independent occasions. The evolution of host breadth exhibited a weaker signal; yet, basal groups were more likely to be host specialists. Both the evolution of lure response and host fruit use provide predictive information for the outbreak management of understudied pest fruit flies for which direct inference of these features may be lacking. Our results, which parallel those of earlier research into the closely-related African Dacus spp., demonstrate how geographically focussed taxon coverage allows Dacini phylogenetics to more explicitly test evolutionary hypotheses, thereby progressing our understanding of the evolution of this highly diverse and recently-radiated group of flies.

Drop-off behaviour of Bt-resistant and Bt-susceptible Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) larvae on Bt-cotton and non-Bt cotton plants.

The highest natural mortality rate of larval Lepidoptera in field populations occurs in the first instar, but it is highly variable. The pattern and degree of survival is not easily predicted but depends on their ability to establish on host plants. Lepidopteran larval dispersal behaviour, known as 'drop-off', happens when the host is unsuitable for larvae to settle and begin feeding. Understanding drop-off behaviour of Helicoverpa armigera (Hübner) with and without physiological resistance to Bt toxins on Bt and non-Bt cotton plants is an important component for resistance management strategies for this insect. We examined the drop-off behaviour of H. armigera to determine: (1) whether they move the same way or differently in response to Bt and non-Bt, and (2) could H. armigera larvae detect Bt toxin levels in cotton plants or did they move independently of toxin levels? In this study, we assessed the drop-off behaviour of Bt-resistant and Bt-susceptible H. armigera neonates on artificial diets and cotton plants with and without Bt toxin during the first 12 h after hatching. Bt-resistant and Bt-susceptible H. armigera neonates behaved differently on Bt and non-Bt substrates. The percentages of Bt-resistant larvae that dropped off Bt and non-Bt cotton plants were not significantly different. In contrast, significantly more Bt-susceptible larvae dropped off Bt cotton than non-Bt cotton plants over time. Although Bt-susceptible larvae could not detect Bt toxin, they showed preference on non-Bt toxin substrates and were more likely to drop off substrates with Bt toxin.

Management and population dynamics of diamondback moth (Plutella xylostella): planting regimes, crop hygiene, biological control and timing of interventions.

Using an age-structured process-based simulation model for diamondback moth (DBM), we model the population dynamics of this major Brassica pest using the cropping practices and climate of Guangdong, China. The model simulates two interacting sub-populations (demes), each representing a short season crop. The simulated DBM abundance, and hence pest problems, depend on planting regime, crop hygiene and biological control. A continuous supply of hosts, a low proportion of crop harvested and long residue times between harvest and replanting each exacerbate pest levels. Biological control provided by a larval parasitoid can reduce pest problems, but not eliminate them when climate is suitable for DBM and under certain planting practices. The classic Integrated Pest Management (IPM) method of insecticide application, when pest threshold is reached, proved effective and halved the number of insecticide sprays when compared with the typical practice of weekly insecticide application.

Temperature-dependent development of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) and its larval parasitoid, Habrobracon hebetor (Say) (Hymenoptera: Braconidae): implications for species interactions.

Habrobracon hebetor (Say) is a parasitoid of various Lepidoptera including Helicoverpa armigera (Hübner), a key pest of different crops and vegetables. The development of both H. armigera and H. hebetor were simultaneously evaluated against a wide range of constant temperatures (10, 15, 17.5, 20, 25, 27.5, 30, 35, 37.5 and 40 °C). Helicoverpa armigera completed its development from egg to adult within a temperature range of 17.5-37.5 °C and H. hebetor completed its life cycle from egg to adult within a temperature range of 15-40 °C. Based on the Ikemoto and Takai model the developmental threshold (To) and thermal constant (K) to complete the immature stages, of H. armigera were calculated as 11.6 °C and 513.6 DD, respectively, and 13 °C and 148 DD, respectively, for H. hebetor. Analytis/Briere-2 and Analytis/Briere-1 were adjudged the best non-linear models for prediction of phenology of H. armigera and H. hebetor, respectively and enabled estimation of the optimum (Topt) and maximum temperature (Tmax) for development with values of 34.8, 38.7, 36.3, and 43 °C for host and the parasitoid, respectively. Parasitisation by H. hebetor was maximal at 25 °C but occurred even at 40 °C. This study suggests although high temperature is limiting to insects, our estimates of the upper thermal limits for both species are higher than previously estimated. Some biological control of H. armigera by H. hebetor may persist in tropical areas, even with increasing temperatures due to climate change.

Behavior as a mechanism of insecticide resistance: evaluation of the evidence.

'Behavioral resistance' must be defined in a manner consistent with other mechanisms of resistance and be based on heritable changes. Most claimed cases of behavioral resistance to insecticides are simply aversion behaviors either learned or based on simple repellency or avoidance. Although studies have shown changes in taste/odour receptors (e.g., cockroaches), unequivocal demonstration of behavioral resistance to insecticides is rare. The fundamental problems are: 1. Inferring resistance from observations, with little evidence of 'normal' behavior prior to exposure to insecticides. 2. Interpreting behaviors as insecticide resistance with no evidence that either resistance is detectable or testing the hypothesis that it is responsible. We suggest a way forward that may not be that novel but would advance our understanding and the field.

A Generalist Herbivore Copes with Specialized Plant Defence: the Effects of Induction and Feeding by Helicoverpa armigera (Lepidoptera: Noctuidae) Larvae on Intact Arabidopsis thaliana (Brassicales) Plants.

Plants of the Brassicaceae are defended from feeding by generalist insects by constitutively-expressed and herbivory-induced glucosinolates (GS). We induced Arabidopsis plants 1, 16 and 24 h prior to allowing neonate larvae of the generalist Helicoverpa armigera to feed on whole plants for 72 h. These plants were subsequently retested with another group of neonates for a further 72 h. We used wild-type A. thaliana Col-0, and mutant lines lacking indolic GS, aliphatic GS or all GS. We hypothesized that larvae would not grow well on defended plants (WT) compared to those lacking GS, and would not grow well if plants had been primed or fed on for longer, due to the expected induced GS. There was survivorship on all lines suggesting H. armigera is a suitable generalist for these experiments. Larvae performed less well on wild-type and no indolic lines than on no aliphatic and no GS lines. Larvae distributed feeding damage extensively in all lines, more so on wild type and no-indolic lines. Contrary to expectations, larvae grew better on plants that had been induced for 1 to 16 h than on un-induced plants suggesting they moved to and selected less toxic plant parts within a heterogeneously defended plant. Performance declined on all lines if plants had been induced for 24 h, or had been fed upon for a further 72 h. However, contrary to expectation, individual and total GS did not increase after these two treatments. This suggests that Arabidopsis plants induce additional (not GS) defenses after longer induction periods.

Oviposition site selection and survival of susceptible and resistant larvae of Helicoverpa armigera (Lepidoptera: Noctuidae) on Bt and non-Bt cotton.

In Australia Bt cotton has been planted since 1996, and has greatly improved the control of its key target Helicoverpa armigera (Hübner). There is no strong evidence that genetically modified cotton has been selected for significant physiological resistance to Bt toxin in field populations. There are many possible explanations for the lack of apparent selection that range from high compliance with the resistance management strategy for this technology to a lack of behavioral preference in key traits such as oviposition that could favor survival. To date most experiments that test oviposition of H. armigera on Bt cotton vs. conventional cotton have been done with susceptible moths. We determine the oviposition preference of a field isolated Bt resistant line of H. armigera and a susceptible counterpart when given a choice of non-Bt cotton and Bt-cotton with the same genetic background, and test whether there is any relationship between oviposition site selection (different plant structures) and the survival of the first instar larvae. Within cotton plants, our experiments consistently showed that both resistant and susceptible moths did not choose plants or plant parts that were less toxic in terms of Bt toxin on which to lay eggs. There was one exception in that susceptible moths were more likely to lay eggs on squares of Bt cotton plants than squares of non-Bt cotton. As expected, the mortality of susceptible H. armigera neonates was significantly higher on structures of Bt cotton plants than on those structures of conventional cotton, and survival was greater on flowers than on other structures of Bt cotton. This confirms opportunities for selection for resistance, and demonstrates no advantage in this respect to carrying resistance genes that might overcome the Bt toxins.

Metarhizium anisopliae infection alters feeding and trophallactic behavior in the ant Solenopsis invicta.

In social insects, social behavior may be changed in a way that preventing the spread of pathogens. We infected workers of the ant Solenopsis invicta with an entomopathogenic fungus Metarhizium anisopliae and then videotaped and/or measured worker feeding and trophallactic behavior. Results showed that fungal infected S. invicta enhanced their preference for bitter alkaloid chemical quinine on 3days after inoculation, which might be self-medication of S. invicta by ingesting more alkaloid substances in response to pathogenic infection. Furthermore, infected ants devoted more time to trophallactic behavior with their nestmates on 3days post inoculation, in return receiving more food. Increased interactions between exposed ants and their naive nestmates suggest the existence of social immunity in S. invicta. Overall, our study indicates that S. invicta may use behavioral defenses such as self-medication and social immunity in response to a M. anisopliae infection.

Population dynamics and management of diamondback moth (Plutella xylostella) in China: the relative contributions of climate, natural enemies and cropping patterns.

Diamondback moth or DBM is the major pest of Brassica vegetable production worldwide. Control has relied on insecticides, and DBM resistance to these compounds has evolved rapidly. We review and summarize data on DBM population dynamics across a large latitudinal gradient from southwest to northeast China: DBM is, on average, more common in southern locations than in northern locations. The species' phenology is consistent: in southern and central locations there is a decline during hot summer months, while in the north, the species can only exist in the summer following migrations from the south. A cohort-based discrete-time model, driven by daily maximum and minimum temperatures and rainfall, which was built using the DYMEX modelling software, captures the age-structured population dynamics of DBM at representative locations, with year round cropping and threshold-based insecticide applications. The scale of the simulated pest problem varies with cropping practices. Local production breaks and strict post-harvest crop hygiene are associated with lower DBM populations. Biological control appears to improve the management of DBM. Of the management strategies explored, non-threshold based applications of insecticides with reduced spray efficacy (due to poor application or resistance) appear the least effective. The model simulates the phenology and abundance patterns in the population dynamics across the climatic gradient in China reasonably well. With planned improvements, and backed by a system of field sampling and weather inputs, it should serve well as a platform for a local pest forecast system, spanning the range of DBM in China, and perhaps elsewhere.

The urticating setae of Ochrogaster lunifer, an Australian processionary caterpillar of veterinary importance.

The bag-shelter moth, Ochrogaster lunifer Herrich-Schaffer (Lepidoptera: Notodontidae), is associated with a condition called equine amnionitis and fetal loss (EAFL) on horse farms in Australia. Setal fragments from O. lunifer larvae have been identified in the placentas of experimentally aborted fetuses and their dams, and in clinical abortions. The gregarious larvae build silken nests in which large numbers cohabit over spring, summer and autumn. The final instars disperse to pupation sites in the ground where they overwinter. Field-collected O. lunifer larvae, their nests and nearby soil were examined using light and electron microscopy to identify setae likely to cause EAFL and to determine where and how many were present. Microtrichia, barbed hairs and true setae were found on the exoskeletons of the larvae. True setae matching the majority of setal fragments described from equine tissue were found on third to eighth instar larvae or exuviae. The number of true setae increased with the age of the larva; eighth instars carried around 2.0-2.5 million true setae. The exuvia of the pre-pupal instar was incorporated into the pupal chamber. The major sources of setae are likely to be nests, dispersing pre-pupal larvae and their exuviae, and pupal chambers.

Effects of Cohabitation on the Population Performance and Survivorship of the Invasive Mosquito Aedes albopictus and the Resident Mosquito Aedes notoscriptus (Diptera: Culicidae) in Australia.

The presence of Aedes albopictus (Skuse) in the Torres Strait of northern Australia increases the potential for colonization and establishment on the mainland. However, there is a possibility that native species that occupy the same habitats may influence the population performance of Ae. albopictus, potentially affecting the establishment of this species in Australia. Cohabitation experiments were performed with the endemic Aedes notoscriptus (Skuse), which has been found occupying the same larval habitats as Ae. albopictus in the Torres Strait and is the most widespread container-inhabiting Aedes species in Australia. The influence of environmental factors and cohabitation between the two species was examined using different climates, food resource levels, food resource types, and species densities. Survivorship proportions and a population performance index (λ') were calculated and compared. The consequences of increased Ae. notoscriptus densities were reduced survivorship and λ' for Ae. albopictus. Despite this, the mean λ' of Ae. albopictus and Ae. notoscriptus was consistently ≥ 1.06, indicating both species could increase under all conditions, potentially due to increasing conspecific densities negatively affecting Ae. notoscriptus. The outcomes from this study suggest that the preexisting presence of Ae. notoscriptus may not prevent the establishment of Ae. albopictus in Australia.

Ability for Aedes albopictus (Diptera: Culicidae) to survive at the climatic limits of its potential range in eastern Australia.

Aedes albopictus (Skuse) is one of the most invasive mosquito species in the world and has infested islands in the Torres Strait, off the northern coast of Australia since at least 2004. This has led to fears that it may establish on the Australian mainland, including highly populated cities in southern temperate regions. To supplement theoretical projections addressing the range expansion of Ae. albopictus into Australia, laboratory-based trials were conducted to assess the performance of a Torres Strait Ae. albopictus population under a range of Australian conditions. First-instar larvae were placed in individual microcosms and maintained on a natural food resource, under average climatic conditions representing different regions of Australia's east coast. Larvae could not survive winter conditions in southern Australia. As the population performance index was >1.0 for tropical winter and summer conditions, and temperate summer conditions, populations would likely increase during these times. To test whether Ae. albopictus could overwinter during adverse conditions as eggs, we exposed cohorts to four different temperature (7, 17, 27, and 33 degrees C) and relative humidity (35, 55, and 80%) combinations for up to 3 mo. High temperatures and low humidity were most detrimental to egg survival. However, those eggs maintained under cooler climates remained viable after 3 mo, including 17% of eggs kept at 7 degrees C. Overall, this study suggests that a Torres Strait Ae. albopictus strain could proliferate all year round under northern tropical conditions and could overwinter in the egg stage before proliferating in the summer in southern temperate regions.

Wolbachia infection does not alter attraction of the mosquito Aedes (Stegomyia) aegypti to human odours.

The insect endosymbiont Wolbachia pipientis (Rickettsiales: Rickettsiaceae) is undergoing field trials around the world to determine if it can reduce transmission of dengue virus from the mosquito Stegomyia aegypti to humans. Two different Wolbachia strains have been released to date. The primary effect of the wMel strain is pathogen protection whereby infection with the symbiont limits replication of dengue virus inside the mosquito. A second strain, wMelPop, induces pathogen protection, reduces the adult mosquito lifespan and decreases blood feeding success in mosquitoes after 15 days of age. Here we test whether Wolbachia infection affects mosquito attraction to host odours in adults aged 5 and 15 days. We found no evidence of reduced odour attraction of mosquitoes, even for those infected with the more virulent wMelPop. This bodes well for fitness and competitiveness in the field given that the mosquitoes must find hosts to reproduce for the biocontrol method to succeed.

Effects of plant availability on population size and dynamics of an insect community: diamondback moth and two of its parasitoids.

To understand the effect of plant availability/structure on the population size and dynamics of insects, a specialist herbivore in the presence of two of its parasitoids was studied in four replicated time-series experiments with high and low plant availabilities; under the latter condition, the herbivore suffered from some periods of resource limitation (starvation) and little plant-related structural refuges. Population dynamics of the parasitoid Cotesia vestalis was governed mainly by the delayed density-dependent process under both plant setups. The parasitoid, Diadegma semiclausum, under different plant availabilities and different coexistence situations (either +competitor or -competitor) showed dynamics patterns that were governed mainly by the delayed density process (significant lags at weeks 2-4). Both the competing parasitoids did not experience beneficial or costly interferences from each other in terms of their own population size when the plant resource was limited. Variation in the Plutella xylostella population under limited plant availability is higher than that under the other plant setup. For both parasitoids, under limited plant setup, the extinction risk was lower when parasitoids were engaged in competition, while under the unlimited plant setup, the mentioned risk was higher when parasitoids competed. In this situation, parasitoids suffered from two forces, competition and higher escaped hosts.

Hybridization and adaptation to introduced balloon vines in an Australian soapberry bug.

Contemporary adaptation of plant feeding insects to introduced hosts provides clear cases of ecologically based population divergence. In most cases the mechanisms permitting rapid differentiation are not well known. Here we study morphological and genetic variation associated with recent shifts by the Australian soapberry bug Leptocoris tagalicus onto two naturalized Neotropical balloon vines, Cardiospermum halicacabum and C. grandiflorum that differ in time since introduction. Our results show that these vines have much larger fruits than the native hosts (Whitewood tree -Atalaya hemiglauca- and Woolly Rambutan -Alectryon tomentosus-) and that bugs living on them have evolved significantly longer beaks and new allometries. Genetic analyses of mitochondrial haplotypes and amplified fragment length polymorphic (AFLP) markers indicate that the lineage of bugs on the annual vine C. halicacabum, the older introduction, is intermediate between the two subspecies of L. tagalicus found on native hosts. Moreover, where the annual vine and Whitewood tree co-occur, the morphology and genomic composition of the bugs are similar to those occurring in allopatry. These results show that hybridization provided the genetic elements underlying the strongly differentiated 'Halicacabum bugs'. In contrast, the bugs feeding on the recently introduced perennial balloon vine (C. grandiflorum) showed no evidence of admixture, and are genetically indistinguishable from the nearby populations on a native host.

Modelling spatio-temporal patterns of long-distance Culicoides dispersal into northern Australia.

Novel arboviruses, including new serotypes of bluetongue virus, are isolated intermittently from cattle and insects in northern Australia. These viruses are thought to be introduced via windborne dispersal of Culicoides from neighbouring land masses to the north. We used the HYSPLIT particle dispersal model to simulate the spatio-temporal patterns of Culicoides dispersal into northern Australia from nine putative source sites across Indonesia, Timor-Leste and Papua New Guinea. Simulated dispersal was found to be possible from each site, with the islands of Timor and Sumba highlighted as the likely principal sources and February the predominant month of dispersal. The results of this study define the likely spatial extent of the source and arrival regions, the relative frequency of dispersal from the putative sources and the temporal nature of seasonal winds from source sites into arrival regions. Importantly, the methodology and results may be applicable to other insect and pathogen incursions into northern Australia.

No evidence for change in oviposition behaviour of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) after widespread adoption of transgenic insecticidal cotton.

Cotton growing landscapes in Australia have been dominated by dual-toxin transgenic Bt varieties since 2004. The cotton crop has thus effectively become a sink for the main target pest, Helicoverpa armigera. Theory predicts that there should be strong selection on female moths to avoid laying on such plants. We assessed oviposition, collected from two cotton-growing regions, by female moths when given a choice of tobacco, cotton and cabbage. Earlier work in the 1980s and 1990s on populations from the same geographic locations indicated these hosts were on average ranked as high, mid and low preference plants, respectively, and that host rankings had a heritable component. In the present study, we found no change in the relative ranking of hosts by females, with most eggs being laid on tobacco, then cotton and least on cabbage. As in earlier work, some females laid most eggs on cotton and aspects of oviposition behaviour had a heritable component. Certainly, cotton is not avoided as a host, and the implications of these finding for managing resistance to Bt cotton are discussed.

Evaluation of long-distance dispersal of Culicoides midges into northern Australia using a migration model.

The introduction of novel bluetongue serotypes and genotypes into northern Australia is considered possible via the long-distance windborne dispersal of Culicoides (Diptera: Ceratopogonidae) vectors from Southeast Asia. Initial findings from simulation modelling of potential dispersal over a 15-year period revealed that the greatest risk for incursion of windborne Culicoides from the island of Timor into northern Australia occurs during December-March. The regions at greatest risk for incursion include the top end of the Northern Territory and the Kimberley region in Western Australia, but there is potential for more widespread dispersal into northern Australia based on Timor as the putative source. The establishment of a more pathogenic strain of the virus, or of a novel Culicoides vector introduced by such inter-continental dispersal events, could dramatically alter Australia's current bluetongue disease status.

Developmental responses of the diamondback moth parasitoid Diadegma semiclausum (Hellén) (Hymenoptera: Ichneumonidae) to temperature and host plant species.

Effects of constant rearing temperature and the plant species fed upon by its hosts were investigated for several developmental parameters of Diadegma semiclausum (Hellén), an important parasitoid of the diamondback moth, Plutella xylostella (L.). Temperature had highly significant effects on all developmental parameters measured, and effects were usually both linear and quadratic with increasing temperature. Host plant species, comprising Brassica napus L., Brassica rapa L. ssp. pekinensis and Brassica oleracea L. var. capitata, also affected development of the parasitoid, and significant interactions were observed between plant species and rearing temperature for all developmental parameters measured. Development of D. semiclausum occurred successfully on all host plant species tested for the temperature range of 10 to 25°C. However, when its P. xylostella hosts consumed leaf tissue of B. napus, no specimens survived to pupate at 30°C, whilst pupation and adult eclosion occurred at 30°C on B. rapa ssp. pekinensis and B. oleracea var. capitata. At high ambient temperatures, such as those characteristic of tropical or subtropical regions (especially at low elevations) or regions that undergo temperature increases due to climate change, P. xylostella is predicted to occur at a higher range of temperatures than its biocontrol agent, D. semiclausum. Effects of high temperatures are expected to be more profound on the parasitoid for some host plants than others, with greater developmental limitations for the parasitoid on B. napus than on B. rapa or B. oleracea.

The movement and distribution of Helicoverpa armigera (Hübner) larvae on pea plants is affected by egg placement and flowering.

The distribution and movement of 1st instar Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) larvae on whole garden pea (Pisum sativum L.) plants were determined in glasshouse trials. This economically-important herbivore attacks a wide variety of agricultural, horticultural and indigenous plants. To investigate the mechanisms underlying larval intra-plant movement, we used early-flowering and wild-type plant genotypes and placed eggs at different vertical heights within the plants, one egg per plant. Leaf water and nitrogen content and cuticle hardness were measured at the different plant heights. Of 92 individual larvae, 41% did not move from the node of eclosion, 49% moved upwards and 10% moved downwards with the distance moved being between zero and ten plant nodes. Larvae from eggs placed on the lower third of the plant left the natal leaf more often and moved further than larvae from eggs placed in the middle or upper thirds. The low nutritive value of leaves was the most likely explanation for more movement away from lower plant regions. Although larvae on flowering plants did not move further up or down than larvae on non-flowering plants, they more often departed the leaflet (within a leaf) where they eclosed. The final distribution of larvae was affected by plant genotype, with larvae on flowering plants found less often on leaflets and more often on stipules, tendrils and reproductive structures. Understanding intra-plant movement by herbivorous insects under natural conditions is important because such movement determines the value of economic loss to host crops. Knowing the behaviour underlying the spatial distribution of herbivores on plants will assist us to interpret field data and should lead to better informed pest management decisions.