Intrinsic competition between larval parasitoids with different degrees of host specificity

Abstract.  1. Interspecific competition among parasitoids may play a key role in the community dynamics of tritrophic plant–herbivore–parasitoid systems and has important implications for management of herbivorous insect pests.
2. A model system was used to explore the outcome of interspecific competition between parasitoids that differ in host specificity. The system included the lepidopteran pest Heliothis virescens , the generalist parasitoid Cotesia marginiventris , and two specialist parasitoids, Microplitis croceipes and Cardiochiles nigriceps .
3. The generalist, C. marginiventris , dominated intrinsic competition when given an 8-h developmental head start over C. nigriceps or when its oviposition was simultaneous with that of M. croceipes . Microplitis croceipes and especially C. nigriceps larvae prevailed when they were allowed to oviposit prior to C. marginiventris .
4. Rates of host mortality prior to parasitoid emergence varied with parasitoid species composition and with the order of oviposition.
5. Implications for integrated pest management and the adaptive significance of competition as related to host specialisation are discussed.     

Influence of adult experience on host microhabitat location by the generalist parasitoid,Campoletis sonorensis (Hymenoptera: Ichneumonidae)

The effect of adult experience on microhabitat location behavior of the generalist parasitoid Campoletis sonorensis (Cameron)was examined in a wind tunnel bioassay. Responses were tested to the odors of two host plants (cotton and sesame) of Heliothis virescens (F.) or a nonhost plant (potato), either damaged and infested with host larvae and host products (host/plant complex) or intact, clean and uninfested. Parasitoid females remained naive or were allowed one oviposition experience on either of the plants, 1 min, 2 h, or 24 h prior their introduction into the wind tunnel. In a no-choice test, parasitoids experienced 1 min prior to bioassay completed significantly more flights to sesame and potato host/plant complexes than did naive parasitoids. However, 24 h after experience, only females experienced on potato completed more flights to the host/ plant complex than did naive females. Parasitoids experienced 1 min prior to flight to undamaged plants showed a slight increase in flight response (significant only for potato) but, after 24 h, completed only as many flights as naive parasitoids. In a dual-choice situation, parasitoids did not show a preference for either of the two host plants but did prefer a host to a nonhost plant. This innate plant preference was not changed by a single oviposition experience. The potential significance of these results to the microhabitat location behavior of C. sonorensisin the field is discussed.     

3种寄主上桃蚜的选择性及形态分化

桃蚜是一种重要的农业害虫,寄主广泛,种下分化复杂。以采自黄土高原旱作区桃树、烟草、甘蓝上的桃蚜为研究对象,通过叶片选择法、传统比较形态测定法研究了3种寄主上桃蚜的选择性及形态分化。结果表明:在3种寄主同时存在的情况下,烟草上的桃蚜嗜食烟草,表现为63.5%的桃蚜选择烟草叶,13.8%选择甘蓝叶,8.2%选择桃叶,而甘蓝和桃树上的桃蚜对原寄主没有表现出明显的嗜好性;从形态指标来看,3种寄主上的桃蚜在体长、触角末节长度、后足腿节长度、触角与体长的比例方面存在显著差异(P0.05),说明这几个特征可以作为区分这3种寄主上桃蚜的依据。综合分析可以初步认为黄土高原旱作区烟草上的桃蚜可能形成了寄主专化型-烟草型。     

Genetic, biochemical, and behavioral uniformity among populations of Myzus nicotianae and Myzus persicae

Prior to designation as distinct species, an appellation presently in question, the tobacco aphid, Myzus nicotianae Blackman (Homoptera: Aphididae), was classified as a tobacco-feeding form of the green peach aphid, Myzus persicae (Sulzer). In this study, RAPD polymorphisms distinguished members of the Myzus persicae complex (M. persicae and M. nicotianae) from three outgroup Myzus species (M. cerasi (F.), M. hemerocallis Takahashi, and M. varians Davidson). Polymorphisms within the complex did not separate populations on the basis of host association (tobacco versus other host plants) or geographic origin (collections from the United States, Europe, and Japan). Similarly, while GC-MS analysis of cuticular hydrocarbon profiles revealed both developmental and inter-populational differences within the M. persicae complex, it did not separate populations of tobacco feeding aphids from those collected off non-tobacco hosts. Finally, with the exception of their responses to a choice between lettuce and collards, the host preference behavior of a green peach aphid population, a red tobacco aphid population, and a green tobacco aphid population was indistinguishable in host preference experiments. These results add to a growing body of evidence suggesting M. nicotianae and M. persicae are conspecific.     

The role of herbivore‐ and plant‐related experiences in intraspecific host preference of a relatively specialized parasitoid

Parasitoids use odor cues from infested plants and herbivore hosts to locate their hosts. Specialist parasitoids of generalist herbivores are predicted to rely more on herbivorederived cues than plant-derived cues. Microplitis croceipes (Cresson)(Hymenoptera: Braconidae) is a relatively specialized larval endoparasitoid of Heliothis virescens (F.)(Lepidoptera: Noctuidae), which is a generalist herbivore on several crops including cotton and soybean. Using M. croceipes/H. virescens as a model system, we tested the following predictions about specialist parasitoids of generalist herbivores:(i) naive parasitoids will show innate responses to herbivore-emitted kairomones, regardless of host plant identity and (ii) herbivore-related experience will have a greater influence on intraspecific oviposition preference than plant-related experience. Inexperienced (naive) female M. croceipes did not discriminate between cotton-fed and soybean-fed H. virescens in oviposition choice tests, supporting our first prediction. Oviposition experience alone with either host group influenced subsequent oviposition preference while experience with infested plants alone did not elicit preference in M. croceipes, supporting our second prediction. Furthermore, associative learning of oviposition with host-damaged plants facilitated host location. I terestingly, naive parasitoids attacked more soybeathan cotton-fed host larvae in two-choice tests when a background of host-infested cotton odor was supplied, and vice versa. This suggests that plant volatiles may have created an olfactory contrast effect. We discussed ecological significance of the results and concluded that both plant- and herbivore-related experiences play important role in parasitoid host foraging.     

Comparison of Host-Searching and Ovipositional Behavior of Cardiochiles nigriceps Viereck (Hymenoptera: Braconidae), a Parasitoid of Heliothis virescens (Fabricius) (Lepidoptera: Noctuidae), in Tobacco and Cotton

To compare host-searching and ovipositional behavior of Cardiochiles nigriceps Viereck (CN) in tobacco and cotton, behavior of CN females was observed on Hellothis virescens (Febricius)-infested plants and recorded using a Psion Organizer II with Observer software. Hover, search, oviposit, preen, rest, walk, agony-search, drop-search, and miss-search were the nine behaviors observed for each plant species. Agony-search was a searching behavior exhibited when CN females were prevented from ovipositing in a host because they were unable to reach the host. Drop-search and miss-search were the searching behaviors that occurred by CN females after a host dropped from the plant and when CN females missed ovipositing in a host, respectively. Hovering, searching, oviposition, miss-search, resting, and walking were equally common for CN on tobacco and cotton. Agony-search was exhibited more on tobacco than cotton, while drop-search and preening occurred more on cotton than tobacco. Female CN spent more time hovering in tobacco than in cotton, indicating that these females preferred tobacco to cotton. Female parasitoids also spent more time in the main ovipositional sequence, hover–search–oviposit, in tobacco than in cotton, mainly because females hovered more in tobacco than in cotton. Frequency and time of behavioral sequences associated with experiencing frustration in ovipositing due to difficulty in reaching or finding a host and subsequent level of success in ovipositing in a new host were determined. Overall, the rate of successful oviposition by CN females was significantly higher in tobacco (87.7%) than in cotton (79.5%). For cotton and tobacco, the rate of successful oviposition by CN females was significantly reduced (ca. 40.0%) when they experienced frustration in ovipositing compared to the rate of ovipositional success (100%) for CN females when hosts were present and easily accessible. Encountering ovipositional frustration also increased the duration of time for successful oviposition in comparison to the time spent for problem-free oviposition in cotton and tobacco. Interestingly, with successful oviposition, the amount of time spent in a behavioral sequence was not significantly different for tobacco and cotton regardless of whether females experienced ovipositional frustration or not. However, female CN invested more time in tobacco than in cotton when they were unsuccessful in ovipositing due to the inaccessibility or disappearance of hosts. CN females' preference for tobacco over cotton probably gave them more motivation to continue searching for hosts, especially those not easily attained, on tobacco than on cotton. Nevertheless, CN females readily searched in cotton for HV even in the presence of host-infested tabacco. CN females possibly could be successful in maintaining levels of HV below an economic threshold when using a tobacco trap crop to protect cotton as the main crop.     

Foraging for solitarily and gregariously feeding caterpillars: A comparison of two related parasitoid species (Hymenoptera: Braconidae)

In the present study we apply a comparative approach, in combination with experimentation, to study behavior of two parasitoid species that attack caterpillar hosts with different feeding strategies (gregarious or solitary). In a semifield setup, consisting of clean cabbage plants and plants infested with one of two host species, the foraging behavior of the specialistCotesia rubecula, on obligate parasitoid of solitarily feedingPieris rapae larvae, was compared to that of the generalistCotesia glomerata, a polyphagous parasitoid of several Pieridae species (mainly the gregariously feedingPieris brassicae).Cotesia glomerata displayed equal propensity to search for and parasitize larvae of both host species. AlthoughC. glomerata exhibited a relatively plastic foraging behavior in that it searched differently under different host distribution conditions, its behavior seems more adapted to search for gregariously feeding hosts. Females exhibited a clear area-restricted search pattern and were more successful in finding the gregariously feeding caterpillars.Cotesia rubecula showed a higher propensity to search forP. rapae than forP. brassicae, i.e., females left the foraging setup significantly earlier when their natural hostP. rapae was not present.C. rubecula showed a more fixed foraging behavior, which seems adapted to foraging for solitarily feeding host larvae. In a setup with onlyP. rapae larvae, the foraging strategies of the two parasitoid species were quite similar. In a choice situationC. glomerata did not show a preference for one of the host species, whileCotesia rubecula showed a clear preference for its natural host species. The latter was shown by several behavioral parameters such as the number of first landings, allocation of search time, and percentage parasitization.     

Foraging behavior of Campoletis sonorensis in response to Heliothis virescens and cotton plants

Wind tunnel flight behavior of inexperienced female Campoletis sonorensis (Cameron) (Hymenoptera; Ichneumonidae) in response to its larval host Heliothis virescens (F.) (Lepidoptera: Noctuidae) feeding on the host plant cotton (Gossypium hirsutum L.) is described. The flight behavioral sequence was determined by quantification of frequencies of observed behaviors and probabilities of first-order behavioral transitions. Comparison of inexperienced C. sonorensis flights to undamaged and damaged cotton indicated that stimuli from undamaged plants alone are adequate to elicit the complete flight behavioral sequence observed in response to H. virescens feeding on cotton.Parasitoid foraging behavior was also analyzed after landing on the stimulus. This behavior appeared to be random in its initial stages, but became sequential after location of evidence of a host. Analysis of foraging on undamaged and 3 treatments of damaged cotton resulted in the determination that parasitoids tend to remain on damaged plants longer than undamaged plants although no significant difference was detected. C. sonorensis spent a greater percentage of their time foraging on host damaged plants than on undamaged plants.

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Résumé Les comportements d'évaluation de l'effectif d'hôtes potentiels et de la position des hôtes par C. sonorensis (Hyméno.: Iccheumonidae) ont été quantifiés pour déterminer les séquences significatives des événements comportementaux. La localisation de la colonie potentielle d'hôtes est apparue comme une séquence régulière des événements comportementaux. Une fois que le parasitoïde a localisé une colonie potentielle, on a constaté que la recherche au hasard des hôtes se poursuit jusqu'à ce qu'il ait la démonstration qu'il s'agit d'une plante attaquée. La localisation par le parasitoïde d'un hôte certain a consitué une autre séquence régulière des événements comportementaux terminant la localisation de l'hôte.L'influence de pieds de coton intacts, de pieds abîmés mécaniquement et de pieds occupés par des chenilles du 3ème stade de l'hôte et de plantes dont les chenilles ont été retirées juste avant l'expérience a été déterminée en modifiant la composition du complexe hôte/plante. Des femelles naïves de C. sonorensis ont montré en présence de pieds de coton intacts apparemment toutes les séquences comportementales de vol impliquées dans la localisation d'une colonie potentielle d'hôtes. Une fois que le parasitoïde a atteint la colonie potentielle d'hôtes, la présence de dégâts de l'hôte n'a pas modifié le temps passé sur la plante, mais a modifié le temps consacré à la prospection.

     

Foraging Efficacy of a Larval Parasitoid in a Cotton Patch: Influence of Chemical Cues and Learning

Plant-herbivore chemical signals and behavioral plasticity may enhance parasitoid host-foraging efficacy in the field; however, no studies have quantified the potential benefits from these factors under field-type conditions. The effect of plant-herbivore signals and learning on the foraging efficacy of Microplitis croceipes was quantified by directly observing and recording total and sequential duration of various foraging behaviors relative to 5 randomly placed herbivore-damaged and host-infested cotton plants and 20 undamaged and non-host-infested plants. Microplitis croceipes spent significantly more time searching (flying and antennation) on host infested versus uninfested plants. Antennation time was significantly and negatively correlated with successive host stings. Contrary to expectations of increased duration, flight time remained constant throughout the foraging bout, which may indicate that there was some learning associated with flight. These results suggest that plant-herbivore chemical signals and learning enhances the foraging efficacy of M. croceipes.     

Volatiles from damaged plants as major cues in long-range host-searching by the specialist parasitoidCotesia rubecula

The role of volatile stimuli in the long-range host-searching behaviour of the specialist parasitoidCotesia rubecula Marshall (Hymenoptera: Braconidae) was studied. Components from the plant-host-complex Brussels sprouts (Brassica oleracea L. var.gemmifera (DC.) Schulz. cv. ‘Titurel’)-Pieris rapae L. (Lepidoptera: Pieridae) were compared for their attractiveness in dual choice tests in a windtunnel. Stimuli from cabbage plants that were mechanically damaged or damaged byP. rapae caterpillars were more attractive to this parasitoid species than stimuli emitted by the host larvae or their faeces. Parasitoids preferred leaves from the plant-host-complex over artificially damaged leaves. Undamaged cabbage plants were the least attractive to the foraging females. These results indicate that in-flight searching behaviour ofC. rubecula is guided by plant-derived information and that for this specialist species more reliable and specific host-derived cues play a minor role at longer distances.     

Polyphagy and primary host plants: oviposition preference versus larval performance in the lepidopteran pest Helicoverpa armigera

Oviposition preference and several measures of offspring performance of Helicoverpa armigera (Hübner) were investigated on a subset of its host plants that were selected for their reputed importance in the field in Australia. They included cotton, pigeon pea, sweet corn, mungbean, bean and common sowthistle. Plants were at their flowering stage when presented to gravid female moths. Flowering pigeon pea evoked far more oviposition than did the other plant species and was the most preferred plant for neonate larval feeding. It also supported development of the most robust larvae and pupae, and these produced the most fecund moths. Common sowthistle and cotton were equally suitable to pigeon pea for larval development, but these two species received far fewer H. armigera eggs than did pigeon pea. Mungbean also received relatively few eggs, but it did support intermediate measures of larval growth and survival. Fewest eggs were laid on bean and it was also the least beneficial in terms of larval growth. Among the host plant species tested, only flowering pigeon pea supported a good relationship between oviposition preference of H. armigera and its subsequent offspring performance. Australian H. armigera moths are thus consistent with Indian H. armigera moths in their ovipositional behaviour and larval performance relative to pigeon pea. The results suggest that the host recognition and acceptance behaviour of this species is fixed across its geographical distribution and they support the theory that pigeon pea might be one of the primary host plants of this insect. These insights, together with published results on the sensory responses of the females to volatiles derived from the different host plant species tested here, help to explain why some plant species are primary targets for the ovipositing moths whereas others are only secondary targets of this polyphagous pest, which has a notoriously broad host range. Handling Editor: Joseph Dickens     

Effects of recent experience on foraging in tephritid fruit flies

In field-cage studies, we investigated how the foraging behavior of tephritid fruit flies is modified by experience immediately prior to release on host plants. We observed females of a relatively monophagous species,Rhagoletis mendax (blueberry maggot fly), an oligophagous species,Rhagoletis pomomella (apple maggot fly), and a polyphagous species,Ceratitis capitata (Mediterranean fruit fly). Just prior to release on a host plant, the following kinds of stimuli were supplied: (1) single oviposition in a host fruit, (2) contact with 20% sucrose, (3) contact with a mixture of protein food (bird feces and sucrose), (4) contact with water, and (5) a walk over a host-plant leaf. When flies foraged on host plants without resources, search was most intensive (as measured by number of leaves visited) following a single oviposition in fruit, but residence time generally was the same following exposure to sugar, protein, and fruit stimuli.Rhagoletis mendax andC. capitata females visited the fewest leaves following exposure to water or host leaves, whereasR. pomonella foraged equally intensively following exposure to food stimuli, water, or leaves. On host plants containing resources (fruit and protein food), a single oviposition dramatically increased the number of females of all three species that found fruit compared to females that received experience with food, water or foliar stimuli. We found no significant effect of recent brief experience with any of the stimuli on subsequent attraction to protein food. Overall,C. capitata exhibited a higher propensity to abandon host plants than eitherR. mendax orR. pomonella. We suggest that this may reflect adaptations to differences in distribution of host plants in nature, strategies of dispersal, and host range.     

Host-specificity and biology ofMetallactus patagonicus [Col.: Chrysomelidae] introduced into Australia for the biological control ofBaccharis halimifolia [Compositae]

Biology and host-specificity of the foliage-feeding chrysomelidMetallactus patagonicus Suffrian were studied in Brazil to determine its suitability for introduction into Australia to control the shrubBaccharis halimifolia L. Multiple-choice host preference testing of plants related toBaccharis and of desirable plants from a range of plant families, showed thatM. patagonicus was restricted toBaccharis spp. It was released in Australia in 1975, but did not establish.      

Candidates for biocontrol of Macfadyena unguis-cati in South Africa: biology, host ranges and potential impact of Carvalhotingis visenda and Carvalhotingis hollandi under quarantine conditions

Macfadyena unguis-cati (L.) Gentry (Bignoniaceae) was introduced as an ornamental in South Africa, but is fast becoming an important invasive plant in many areas. It is difficult to control the plant chemically and mechanically. The first biocontrol agent, the chrysomelid Charidotis auroguttata (Boheman), has been released. It established at some release sites, but numbers have so far remained low. Additional biocontrol agents were sought to augment C. auroguttata. The potential host ranges of two foliage feeding lace bugs, Carvalhotingis visenda (Drake and Hambleton) and C. hollandi (Drake) (Hemiptera: Tingidae) were evaluated on the basis of nymphal no-choice and adult multi-choice tests involving 23 plant species in 11 families. In no-choice tests, nymphs of both species were able to survive and complete development on M. unguis-cati only, and adults of both species only fed and oviposited on M. unguis-cati during the adult multi-choice tests. Host specificity tests thus confirm that the tingids are highly host specific biocontrol agents, and will not pose risk to any non-target plants in South Africa. A study to determine the potential impact of C. hollandi nymphal feeding on M. unguis-cati showed a significant decrease in the chlorophyll contents of leaves when compared to those of control plants. These studies indicate that, once released, the two lace bug species could contribute significantly to the biological control of M. unguis-cati in South Africa.     

Nitrogen and water affect direct and indirect plant systemic induced defense in cotton

Plants have direct and indirect constitutively produced and inducible defenses against herbivores and pathogens, which can substantially aid in their ability to defend themselves. However, very little is known about the influence of agronomic factors on such defenses. Here, we tested the effects of nitrogen levels and water availability on the ability of cotton plants to deter feeding by Spodoptera exigua through induction of anti-feedants, and to attract Microplitis croceipes through systemic induction of volatile emission. Cotton plants were grown with various nitrogen levels and were either exposed to water stress or normal water before being exposed to S. exigua for 48 h for induction of defenses. Dual choices of various nitrogen and water treatments were provided to M. croceipes in flight tunnel bioassays. Dual choices of leaf tissue from the various nitrogen and water treatments were provided to S. exigua larvae. Both water stress and nitrogen levels under and over the recommended levels increased leaf tissue consumption and decreased attraction of M. croceipes to the plants. Analyses of induced volatiles released from herbivore damaged plants indicate that their concentrations differ among the nitrogen levels tested with plants receiving no nitrogen or twice the recommended dose having amounts much lower than plants receiving the recommended dose. Because both direct and indirect plant defense mechanisms are negatively affected by improper nitrogen and insufficient water, we argue that these factors should be considered for a better natural control of pests in cotton and most probably in other crops.     

Individual variation in two host plants of the ladybird beetle,Epilachna pustulosa (Coleoptera: Coccinellidae)

Individual variation in two species of host plants (thistle,Cirsium kamtschaticum, and blue cohosh,Caulophyllum robustum) of the herbivorous ladybird beetleEpilachna pustulosa was examined under laboratory conditions for their acceptability to adult beetles as a food resource, for adult preference and for larval performance. When clones of these plants were subjected to non-choice tests using posthibernating female beetles, there was found to be significant intraspecific variation among clones in terms of their acceptability, but interspecific variation was not detected. Significant intraspecific as well as interspecific variation were frequently detected in the two host plants when clones of these plants were subjected to choice tests using posthibernating female beetles; the magnitude of interspecific plant variation for beetle preference is not necessarily larger than that of intraspecific plant variation. Individual variation across plant species with respect to beetle larval performance was also significant. A positive correlation between adult preference and larval performance is suggested across the two taxonomically remote host plant species, thistle and blue cohosh, although this needs further investigation.     

Effects of postemergence experience on searching and landing responses of the insect parasitoid,Cotesia congregata (Say) (Hymenoptera: Braconidae), to plants

Postemergence experience with one of six plant species, in the presence of the host larva, modified the searching response of reproductively mature females of Cotesia congregata(Say) to these plants in at least one of three ways: (1) an increased response to the plant experienced at emergence, (2) an increased response to other plants, or (3) an inhibited response to other plants. Landing and searching responses were differentially affected by postemergence experience. For example, postemergence experience with tobacco (a common plant) in the presence of the host larva induced a landing preference for this plant over parsley (a novel plant) but did not affect searching responses to either plant, whereas experience with parsley and the host larva induced an increased searching response to parsley but a landing preference for tobacco. Differential effects of postemergence experience may reflect the type of stimuli involved in searching or landing and may have adaptive significance.     

Flight responses in a wind tunnel of the parasitoid Microplitis croceipes to three spring and three summer host plants of Heliothis spp.

Flight responses of the parasitoid, Microplitis croceipes (Cresson) (Hymenoptera: Braconidae) to two phenological stages of spring host plants (crimson clover, Trifolium incarnatum L., hairy vetch, Vicia villosa Corbiere, and cutleaf geranium, Geranium dissectum L.) and summer host plants (cotton, Gossypium hirsutum L., sorghum, Sorghum bicolor L., and soybean Glycine max (L.) Merr.) of Heliothis virescens (F.), were measured in a dual choice situation in a wind tunnel. Preflowering clover was more attractive than preflowering geranium, followed by preflowering vetch. Clover was preferred over geranium in flowering stages as well. No within species differences were detected for the two phenological stages. Preflowering and flowering cotton and soybean were preferred over preflowering and flowering sorghum. The findings could be important in pre-determining release sites for M. croceipes in the field.     

The biology of two Eretmocerus spp. (Haldeman) and three Encarsia spp. Forster and their potential as biological control agents of Bemisia tabaci biotype B in Australia

The performance, as measured by daily rate of parasitism and total parasitism, of five aphelinid species found in Australia parasitising Bemisia tabaci were compared on cotton, hibiscus, rockmelon, soybean and tomato. Two Eretmocerusspp., both indigenous to Australia, gave the highest levels of parasitism on each of the plant host species tested. The tritrophic interactions between B. tabaci, host plant species and Eret. mundus(Australian parthenogenetic form) (APF) were also examined. In general, more whiteflies were parasitised when cotton was the source host or rockmelon the test host. Parasitism was always low when tomato was either the source or test host. When parasitoids were transferred from rockmelon to cotton, parasitism declined. In contrast, parasitism increased when parasitoids were transferred from cotton to rockmelon. Parasitism also increased when parasitoids were transferred from soybean to rockmelon, yet failed to do so when shifted from soybean to cotton despite cotton normally being a better host. However, when parasitoids were transferred from cotton to soybean there was a marked increase in parasitism. Possible causes are discussed. The field cage trial demonstrated that parasitism by both Eretmocerus spp. increased with increasing whitefly density. Further, the increase in parasitism was not due to the presence of more parasitoids as neither the parasitoid-whitefly ratio nor the total number of parasitoids present had a significant effect on parasitism. The combination of the two species, gave similar levels of parasitism to that achieved by Eret. mundus(APF) alone. Subsequent identification of the emerged individuals indicated that over 50% of the parasitism was due to this species suggesting that it out-competed Eret. queenslandensis. Despite this competition, there was no evidence that overall control was compromised.     

Movement patterns of an Australian chrysomelid beetle in a stand of two Eucalyptus host species

Summary We examined the movements of Chrysophtharta hectica, a eucalypt-feeding chrysomelid beetle in New South Wales, Australia, in relation to the beetle's sex, age and life-history, and to attributes of its Eucalyptus host plants. Beetle movements within the site were not influenced by beetle age or sex, but may be related to generation. Beetle distributions on the two host plant species, Eucalyptus stellulata and E. pauciflora, were generally clumped. Some of this clumping resulted from preference for E. stellulata over E. pauciflora. Clumping of beetles also occurred within host plant species; some plant individuals were consistently heavily used by beetles over the course of three years. We examined nutritional, spatial and biomass attributes of plants and found plant height and foliage production to be the best predictors of beetle numbers.