Conspecific Nymphs Research Articles

Adaptive changes in pheromone production and release under rearing conditions in stink bugs.

Healthy cultures of arthropods are important for pest management programs (e.g. biocontrol). Little is known about how rearing conditions may affect pheromonal interactions. We investigated how rearing histories and densities affect pheromone emission/production in two stink bug species (Hemiptera: Heteroptera), the predatory bug Arma custos, a biocontrol agent, and the bean bug Riptortus pedestris, a pest on legume crops. Nymphs from newly established laboratory colonies of both species produced higher amounts of the defense (dispersal) compound, 4-oxo-(E)-hexenal (OHE), in the presence of conspecific nymphs. Also, when two or more A. custos males were placed together, the dorsal abdominal glands (DAGs) ceased to release aggregation pheromone, whereas the metathoracic glands (MTGs) increased the emission of defensive odors. These changes resulted from exposure to conspecific pheromone odors, as confirmed by exposing bugs to pheromone standards. Hence, pheromone emissions in these stink bugs are readily changed in response to the odors of conspecifics, which may become a problem after long-term rearing. Indeed, an old laboratory colony of A. custos (~30 generations) exhibited less-developed DAGs and reduced pheromone production. Instead, males released significantly more defensive odors from the enlarged MTGs. Furthermore, long-term rearing conditions appeared to favor nymphs that were able to share space with conspecifics by releasing less OHE, which has not yet occurred in the new laboratory colonies. Rearing density affects pheromone release in newly established laboratory colonies of stink bug species, whereas long-term rearing results in new pheromonal compositions coinciding with adaptive changes in gland development. © 2023 Society of Chemical Industry.

Can parasitism by Tamarixia radiata (Hymenoptera: Eulophidae) affect the movement and oviposition behavior of Diaphorina citri (Hemiptera: Psyllidae)?

Diaphorina citri is the vector of the bacterium that cause “huanglongbing” (HLB). The psyllid acquires the pathogen after feeding on infected plants and transmits it to other trees as it moves through the orchard. The psyllid’s movement is directly affected by abiotic and biotic factors, such as the presence of conspecific insects and natural enemies. We evaluated the effects of the presence of conspecific nymphs either not parasitized or parasitized by Tamarixia radiata on the movement and oviposition of adult female D. citri. Diaphorina citri females were released into cages containing a row of four equidistant Murraya paniculata plants. The first plant, the release point, had one of three conditions: no nymphs; non-parasitized nymphs (high and low densities); or previously parasitized nymphs. At 24, 48, and 72 h following release, the females on each plant in the cage were counted. At the end of the observations (72 h), the females were removed, and the eggs laid on the plants were counted. The presence of non-parasitized nymphs, at low and high densities, increased the tendency of adult movement and reduced the total number of laid eggs, compared with cases in which nymphs were absent. On the other hand, the presence of nymphs increased the egg distribution by females over all available plants in the cages. In these cases, higher number of adult females and eggs were observed in plants without nymphs, compared with the plant in which nymphs were present (release point). The conditions of nymphs, i.e., if parasitized or not, did not change the movement behavior and the distribution of eggs deposited over plants in the cages. However, the number of eggs laid by females was low for the cases in which the nymphs were parasitized. The findings can contribute to establishing the optimal of application of the psyllid management techniques, and improving the efficiency of natural enemy releases considering that the pest can be present at the field in different life stages.

Maternal Aggression and Juvenile Sociality in Hibiscus Harlequin Bugs

Hibiscus harlequin bugs (Tectocoris diophthalmus) are Australian jewel bugs known for their maternal care behavior, gregariousness and warning coloration. They feed on plants in the Malvaceae family, although the nymphs will also cannibalize unguarded eggs. Here, I detail observations over 3-year period in Brisbane (QLD), mostly on cultivated Hibiscus and Malvaviscus varieties, to quantify the frequencies at which nymphs and adults occur in groups and the sizes of these groups. I also performed manipulative experiments where I placed individuals together to form groups, or to threaten females guarding a clutch of eggs, and recorded their responses. I observed that harlequin bugs repeatedly colonized a select few individual bushes in sunny locations within the study area. Egg guarding females defended against both conspecific nymphs and adult bugs placed next to the eggs, but rarely responded to the eggs being touched directly with my finger. Nymphs were far more commonly in groups than solitary, and often appeared to aggregate with non-siblings. Further, nymphs inserted into groups mostly remained there. Adults were usually solitary, and typically moved apart if placed together. I suggest that differences in the typical coloration of nymphs (shiny blue) and adults (orange) and possible dual functions as warning and camouflage might explain why nymphs are vastly more social than adult bugs.

Intraguild predation and cannibalism among Dicyphini: Dicyphus cerastii vs. two commercialized species

AbstractDicyphine mirids are one of the most important groups of predators on tomato. In the Mediterranean region, several species in the genera Dicyphus, Macrolophus, and Nesidiocoris (Hemiptera: Miridae, Bryocorinae, Dicyphini) colonize protected horticultural crops. In Portugal, Nesidiocoris tenuis (Reuter) is increasingly abundant in the mirid species complex of tomato crops and appears to be displacing the native Dicyphus cerastii Wagner. In order to know whether intraguild predation (IGP) can explain the decreasing abundance of D. cerastii, we evaluated predatory interactions between adult females and first instars of D. cerastii vs. N. tenuis but also D. cerastii vs. Macrolophus pygmaeus (Rambur), as this species is also naturally present in horticultural crops in Portugal. Cannibalistic interactions were also tested for the same three species. All experiments were performed under laboratory conditions, in Petri dish arenas, in the presence or absence of Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) eggs as alternative prey. Predation on both heterospecific and conspecific nymphs occurred only in the absence of alternative food. Intraguild predation was mutual and symmetrical between D. cerastii and M. pygmaeus. However, IGP was asymmetrical between D. cerastii and N. tenuis, favouring the first. Cannibalism was not significantly different among these mirid species. Our results show that D. cerastii has a greater capacity to feed on intraguild prey than N. tenuis. Therefore, IGP on small nymphs does not explain the abundance shift between D. cerastii and N. tenuis.

Behavioural and electrophysiological responses ofTriatoma dimidiata nymphs to conspecific faecal volatiles.

The behavioural and electrophysiological (electroantennography) responses of the first two instars of Triatoma dimidiata (Hemiptera: Reduviidae) Latreille to fresh and dry faecal headspace volatile extracts from fifth instar conspecific nymphs and synthetic compounds were analysed in this study. Recently emerged nymphs (3-5 days) aggregated around filter paper impregnated with dry faeces and around filter paper impregnated with extracts from both fresh and dry faeces. Older first instars (10-15 days) and second instars aggregated around filter paper impregnated with fresh and dry faeces, and their respective headspace extracts. Dry faecal volatile extracts elicited the strongest antennal responses, followed by fresh faecal extracts. Gas chromatography-mass spectrometry analysis of dried faecal headspace volatiles demonstrated the presence of 12 compounds: 2-ethyl-1-hexanol, 1,2,4-trimethylbenzene, n-octadecane, n-nonadecane, n-eicosane, n-heneicosane, n-tricosane, n-pentaeicosane, n-hexaeicosane, n-octaeicosane, nonanal, and 4-methyl quinazoline. In fresh faecal headspace extracts, only nonanal was clearly detected, although there were other trace compounds, including several unidentified sesquiterpenes. Four of the 11 compounds tested individually elicited aggregation behaviour at concentrations of 100 ng/µL and 1 µg/µL. A blend containing these four components also mediated the aggregation of nymphs. These volatiles may be valuable for developing monitoring methods and designing sensitive strategies to detect and measure T. dimidiata infestation.

Cannibalism in Amblyseius largoensis (Muma) (Acari: Phytoseiidae), an important natural enemy of coconut mite pests

ABSTRACTThe phytoseiid mite Amblyseius largoensis (Muma) is an important natural enemy of two key coconut pests, the red palm mite, Raoiella indica Hirst (Acari: Tenuipalpidae), and the coconut mite, Aceria guerreronis Keifer (Acari: Eriophyidae). Amblyseius largoensis is considered a generalist due to its ability to feed on multiple food sources (e.g. phytophagous mites, small insects, plant exudates, nectar, and pollen). Specimens of A. largoensis sometimes attack each other in competitive situations. Thus, we hypothesized that intraspecific interactions, such as cannibalism, may occur when heterospecific prey are scarce. Experiments were conducted to determine whether, and to what extent, the availability of heterospecific prey, eggs of R. indica, influenced the tendencies of A. largoensis to cannibalise. Additionally, the oviposition of A. largoensis was measured in the presence and absence of both conspecific nymphs and R. indica eggs. Overall, in the absence of the heterospecific prey, A. largoensis consumed conspecific nymphs, and few eggs were produced, whereas in the presence of abundant herbivorous prey, cannibalism decreased, and oviposition increased. These results suggest that, similar to other phytoseiid mites, A. largoensis employs cannibalism as an adaptive survival strategy when heterospecific prey is absent or scarce.

Cannibalism: Do risks of fighting and reprisal reduce predatory rates?

Cannibalism is a common phenomenon among insects. It has raised considerable interest both from a theoretical perspective and because of its importance in population dynamics in natural ecosystems. It could also play an important role from an applied perspective, especially when using predatory species in biological control programmes. The present paper aims to study the cannibalistic behaviour of Nabis pseudoferus Remane and the functional response of adult females. In a non-choice experiment, adult females showed clear acceptance of immature conspecifics as prey, with relatively high mortality values (51.89 ± 2.69%). These values were lower than those occurring for heterospecific prey, Spodoptera exigua Hübner, under the same conditions (80.00 ± 2.82%). However, the main result was that the rate of predation on heterospecific prey was reduced to 59.09 ± 7.08% in the presence of conspecific prey. The prey-capture behaviour of adult females differed when they hunted conspecific versus heterospecific prey. This was shown in the average handling time, which was 23.3 ± 3.3 min in the first case (conspecific) versus 16.6 ± 2.5 min in the second (heterospecific). Furthermore, the values increased in the former case and declined in the latter according to the order in which the prey were captured. The difference in handling time was not significant when adjusting the adult female functional response to conspecific nymphs. We argue that these results likely indicate risk aversion and a fear of reprisal among conspecifics.

Female Sex Pheromone in Trails of the Minute Pirate Bug, Orius minutus (L).

Orius minutus (L.) (Heteroptera: Anthocoridae) is a natural enemy of agricultural pests such as thrips, aphids, and various newly hatched insect juveniles. In this study, we conducted 1) behavioral assays for evidence of contact sex pheromone activity in trails of O. minutus, and 2) chemical analysis to identify the essential chemical components of the trails. Males showed arrestment to trails of mature virgin females but not to trails from either conspecific nymphs or immature females. Females also showed arrestment to trails from conspecific males, although the response was weaker than that exhibited by males. The activity of female trails lasted for at least 46 h after deposition. Males showed a response irrespective of mating experience. Following confirmation that a contact sex pheromone was present in the trails of female O. minutus, we used a bioassay-driven approach to isolate the active chemicals. After fractionation on silica gel, the n-hexane fraction was found to be biologically active to males. A major compound in the active fraction was (Z)-9-nonacosene; this compound was found only in trail extracts of mature virgin females. Synthetic (Z)-9-nonacosene arrested O. minutus males, indicating that it is the major active component of the contact sex pheromone in the trails of female O. minutus.

Intraguild Predation And Cannibalism Among Mite Predators: Stethorus gilvifrons (Mulsant) (Coleoptera: Coccinellidae), Orius albidipennis (Reuter) (Hemiptera: Anthocoridae) And Scolothrips longicornis Priesner (Thysanoptera: Thripidae)

Stethorus gilvifrons (Mulsant), Orius albidipennis (Reuter) and Scolothrips longicornis Priesner are the key predators of Tetranychus urticae in Egypt. In this study, the intraguild predation (IGP) and cannibalism of adult females of these predators were studied under laboratory conditions. Data revealed that in the absence of extra guild prey (T. urticae), the adult females of IG predator S. gilvifrons consumed more larvae or nymphs of IG prey species than IG predators of O. albidipennis or S. longicornis. Females of S. gilvifrons showed significantly a higher predation rate on heterospecific young and old nymph instars of O. albidipennis than on S. longicornis. Interactions of adults S. gilvifrons and larvae or nymphs of O. albidipennis or S. longicornis were highly asymmetric or unidirectional predation always being the IG predator. S. gilvifrons had stronger intraguild predator than O. albidipennis or S. longicornis. Intraguild predation could be considered mutual between O. albidipennis and S. longicornis but there is neither predation nor egg deposition occurred on young or old larvae of S. gilvifrons. The IG predator O. albidipennis showed higher predation rate on S. longicornis than on conspecific nymphs. Whereas, S. longicornis showed high predation rate on conspecific larvae. Females of S. gilvifrons provided with conspecific or heterospecific young and old larvae or nymphs were able to lay eggs when fed on S. gilvifrons, O. albidipennis and S. longicornis. Also, O. albidipennis and S. longicornis laid eggs when fed on conspecific or heterospecific young and old larvae or nymphs except when fed on larvae of S. gilvifrons as IG prey. Obviously, the presence of T. urticae led to significant decrease in IGP.

Volatile compound diversity and conserved alarm behaviour in Triatoma dimidiata.

BackgroundTriatoma dimidiata (Latreille) is a key vector complex of Trypanosoma cruzi, etiologic agent of Chagas disease, as it spans North, Central, and South America. Although morphological and genetic studies clearly indicate existence of at least five clades within the species, there has been no robust or systematic revision, or appropriate nomenclature change for species within the complex. Three of the clades (haplogroups) are distributed in Mexico, and recent evidence attests to dispersal of clades across previously “presumed” monotypic geographic regions. Evidence of niche conservatism among sister species of this complex suggests that geographic dispersal is possible for non-sympatric populations, although no information is available on the behavioural aspects of potential interclade interactions, for instance whether differentiation of chemical signaling or response to these signals could impede communication among the haplogroups.MethodsVolatiles emitted by disturbed bugs, Brindley’s (BGs), and metasternal (MGs) glands were identified using solid-phase micro-extraction (SPME) and gas chromatography coupled mass spectrometry (GC-MS). Volatile compounds emitted by BGs and MGs, and those secreted by disturbed nymphs and adults, of the three Mexican T. dimidiata haplogroups were tested for avoidance behaviour by conspecific nymphs and adults using an olfactometer.ResultsTriatoma dimidiata haplogroups all have three age-related alarm responses: absence of response by early stage nymphs, stage-specific response by 4-5th stage nymphs, and a shared 4-5th nymph and adult response to adult compounds. Disturbed bugs released 15 to 24 compounds depending on the haplogroup, among which were three pyrazines, the first report of these organoleptics in Triatominae. Isobutyric acid from BGs was the most abundant molecule in the response in all haplogroups, in addition to 15 (h1) to 21 (h2 and h3) MG compounds. Avoidance behaviour of disturbed bugs and volatiles emitted by BGs were haplogroup specific, while those from the MG were not.ConclusionsDiscriminant and cluster analysis of BG + MG compounds indicate significant separation among the three haplogroups, while alarm response compounds were similar between h2 and h3, both distinct from h1. This latter haplogroup is ancestral phylogenetically to the other two. Our results suggest that alarm responses are a conserved behaviour in the Triatoma dimidiata complex.

Filling dynamics of the Brindley’s glands in the blood-sucking bug Triatoma infestans (Hemiptera: Reduviidae)

The filling dynamics of exocrine defensive glands is an important component of the defensive capacity of an insect in its natural environment. We studied the filling state and reloading rate of the Brindley’s glands in the haematophagous Chagas disease vector Triatoma infestans (Hemiptera: Reduviidae). Quantitative analyses of isobutyric acid, the main secretion component, were carried out with glands dissected from adults under different scenarios of development, number of discharging events and feeding conditions. The alarm-pheromone function of the gland secretion was also assessed in bioassays with conspecific nymphs. Although pharate adults have their glands completely developed, these were not full until imaginal ecdysis. If kept undisturbed, the adults maintained a constant gland load, and discharged about 75% of the gland contents upon one disturbance event. While the glands can be discharged several times, full replenishing was not complete after one week, unless the insect had access to food. The escape behavior of nymphs in bioassays correlated with the chemical analyses, with nymphs showing significant avoidance only toward gland discharges from undisturbed or disturbed/fed adults. The results are discussed in reference to the feeding frequency and gregarious behavior of T. infestans under natural conditions, which suggest a relevant role of the filling dynamics of the Brindley’s glands in the intraspecific communication of the insect.

Does it Pay to Care?: Exploring the Costs and Benefits of Parental Care in the Hibiscus Harlequin BugTectocoris diophthalmus(Heteroptera: Scutelleridae)

AbstractKnowledge of the selective pressures favouring parental care can inform our understanding of the evolutionary origins and transitions of sociality in insects. Here, we report upon investigations designed to estimate the costs and benefits of parental care in the egg‐guarding hibiscus harlequin bugTectocoris diophthalmus(Heteroptera:Scutelleridae). We found that the presence of a guarding female had no effect on hatching success under benign laboratory conditions. In the wild, however, guarding decreased the likelihood of total clutch failure, and produced a fourfold greater egg‐hatching rate relative to unguarded clutches. Females guarded against generalist invertebrate egg predators, including conspecific nymphs, but were ineffective against hymenopteran egg parasitoids. Females continued to feed during the guarding period and exhibited no signs of weight loss or increased mortality due to this behaviour. We did not observe the production of subsequent clutches in any experimental females; therefore, the lifetime fecundity costs of providing parental care inT. diophthalmusremain indeterminate. Overall, maternal egg guarding appears to function as a relatively low cost–low benefit strategy that increases hatching success by protecting against predation – but not parasitism.

Previous infestation of pea aphids Acyrthosiphon pisum on broad bean plants resulted in the increased performance of conspecific nymphs on the plants

We studied the effects of previous infestation of broad bean plants by pea aphids Acyrthosiphon pisum on the performance of conspecific nymphs on the plants and the involvement of jasmonic acid (JA)-related defenses. The time needed for newly emerged nymphs to become reproductive adults on broad bean plants previously infested by conspecifics (pre-infested plants) was significantly shorter than on uninfested (control) broad bean plants. The total numbers of nymphs produced by aphids on preinfested and control plants were not significantly different. Preinfested plants produced significantly less endogenous JA than that control plants did. To test the effect of JA decreases, we conducted experiments on the developmental duration of nymphs on broad bean plants treated with JA (JA-treated plants) before infestation. The time needed for nymphs to become reproductive adults on JA treated preinfested broad bean plants was not significantly different from that on JA-treated control plants. The results suggested a possible parental care by pea aphids: the adult aphids manipulated JA-related defenses in broad bean plants that had positive effects for their offspring.

Do desert locust hoppers develop gregarious characteristics by watching a video?

Various sensory stimuli have been suggested to induce gregarious body coloration in locusts, but most previous studies ignored the importance of substrate color. This study tested the effects of visual, olfactory and tactile stimuli from other locusts on the induction of gregarious body coloration in single (isolated-reared) Schistocerca gregaria nymphs housed in yellow–green cups. Odor from gregarious (crowd-reared) locusts, which is believed to induce black patterns in single locusts, had little effect when applied to visually isolated nymphs at the 2nd stadium onward, and all test nymphs remained green without black patterns at the last stadium, as in controls reared without odor and visual stimuli. Visual stimuli alone induced black patterns when a single solitarious nymph was allowed to see other locusts in another cup. The degree of black patterns increased as the number of locusts shown increased, and some test nymphs developed body coloration typically observed in gregarious forms. A classical morphometric ratio (hind femur length/head width) shifted toward the value typical of gregarious forms when the single nymphs were allowed to see 5 or 10 locusts. Single nymphs also developed black patterns when presented green conspecific nymphs and adults of two hemipteran species kept in another cup. No synergetic effects of visual and odor stimuli were detected. Movies of locusts, crickets and tadpoles were found effective in inducing black patterns in single locusts. Ontogenetic variation in the sensitivity to crowding and experimental methodology might be responsible for some discrepancies in the conclusions among different researchers.

Toxic associations: A review of the predatory behaviors of millipede assassin bugs (Hemiptera: Reduviidae: Ectrichodiinae)

Ectrichodiinae (Hemiptera: Reduviidae), the millipede assassin bugs, are a speciose group (>660 species) of assassin bugs that appear to be specialist predators on Diplopoda, or millipedes. Apparently capable of coping with the noxious defensive compounds produced by many millipedes, Ectrichodiinae are engaged in a predator-prey relationship with millipedes realized only by few other arthropods. Unfortunately, feeding behaviors of Ectrichodiinae are inadequately documented, rendering this exciting phenomenon largely inaccessible. We here present a literature review on ectrichodiine prey selection and feeding behaviors, with supplemental original observations on Rhiginia cinctiventris (Stål, 1872) in Costa Rica. Thirteen species in 12 genera have been observed to feed on millipedes. The majority of diplopod prey species were reported from the orders Spirostreptida and Spirobolida, whereas Polydesmida are rarely attacked. Ectrichodiinae insert their stylets at the millipede's intersegmental membranes on the ventral and ventro-lateral trunk area or between the head and collum. Communal predation was observed among conspecific nymphs, among groups of nymphs with a conspecific adult, and more rarely among adults. Immature ectrichodiines were rarely observed to engage in solitary predation. Observations on R. cinctiventris indicate that this species preys on spirobolid and polydesmid millipedes and are in agreement with behaviors described for other Ectrichodiinae.

Pheromonal Cross-Attraction in True Bugs (Heteroptera): Attraction of Piezodorus hybneri (Pentatomidae) to Its Pheromone Versus the Pheromone of Riptortus pedestris (Alydidae)

We investigated the attractiveness of a synthetic form of the pheromone of the soybean stink bug, Piezodorus hybneri (Gmelin), under field conditions, and compared it with that of (E)-2-hexenyl (E)-2-hexenoate, a pheromone component of a competitor, Riptortus pedestris (Fabricius). Many adult stink bugs were attracted to traps baited with 100 mg of the synthetic pheromone (1: 1: one mixture of β-sesquiphellandrene, (R)-15-hexadecanolide, and methyl (Z)-8-hexadecenoate), but few were attracted to 1 or 10 mg. More than twice as many females as males were attracted to this male-produced pheromone. None of the individual pheromone components (30 mg) attracted conspecifics. In summer (June-July), when field P. hybneri were not in diapause, (E)-2-hexenyl (E)-2-hexenoate was more attractive to P. hybneri than the synthetic pheromone. The sex ratio of the adults attracted to the synthetic pheromone was highly female-biased, yet almost equal numbers of both sexes were attracted to (E)-2-hexenyl (E)-2-hexenoate. Most females attracted to both attractants were mated and had mature ovaries. However, adults attracted to (E)-2-hexenyl (E)-2-hexenoate were likely to have less food in their stomach than those attracted to the synthetic pheromone. In late autumn (October-November), when the bugs were in reproductive diapause, both attractants attracted many sexually immature female and male adults that had well-developed fat body. The synthetic pheromone also attracted a large number of conspecific nymphs. These results suggest that P. hybneri pheromone and R. pedestris pheromone component, respectively, have different functions for P. hybneri. The male-produced pheromone system of P. hybneri seems to be sex-related but to have other roles.

Weakly aggressive behaviour towards nymphs in the cockroach Schultesia nitor (Blattaria: Zetoborinae)

This paper describes aggressive behaviour in the cockroach Schultesia nitor, a tropical forest species living in bird nests. Young S. nitor nymphs are known to show active dispersal while old nymphs and adults are contrastingly strongly gregarious, a combination of features never observed in other cockroach species. Our laboratory experiments using video recording of confrontations between pairs show that aggressive behaviour towards conspecific nymphs is not exhibited towards nymphs of the species Phoetalia pallida, and thus can be considered species specific in S. nitor. But, it is not kin oriented: the mother and all adults of both sexes in different physiological states exhibit this behaviour as well. Six types of aggressive interactions were discriminated, occurring in age-symmetric pairs of nymphs and adults. Even more frequent aggression was exhibited by adults and last instar nymphs towards younger nymphs of all instars. The frequency of aggressive acts and types of aggressive interactions varied according to sex and size of the two interacting individuals. The possible function and evolution of this behaviour is discussed, with emphasis on the difficulty of interpreting obvious but weak and not kin-biased aggression.

Plant and Prey Consumption Cause a Similar Reductions in Cannibalism by an Omnivorous Bug

Cannibalism is usually more intense when other food sources are scarce, be it prey or plant-based foods. We hypothesized that feeding on plants would reduce cannibalism to a lesser extent than feeding on prey, because plants are considered nutritionally inferior compared to prey. We used the omnivorous bug Orius laevigatus Say (Heteroptera: Anthocoridae) to test this prediction. Starved female bugs were individually held with five second-instar conspecific nymphs and offered (i) Helicoverpa armigera eggs (prey); (ii) pollen (plant); (iii) H. armigera eggs and pollen (prey + plant); or (iv) no eggs or pollen. Fewer cannibalistic events and shorter feedings on conspecifics were recorded in the presence of pollen, prey or both than in their absence. Data therefore do not support our hypothesis that cannibalism is differentially affected by foods of different nutritional values. It seems that omnivorous feeding habits enable predators to sustain themselves on plant sources in the absence of prey, without the need to resort to cannibalism.

Age‐dependent response of adults of a homochrome grasshopper, Oedipoda miniata, to the dark‐colour‐inducing neurohormone (DCIN) of locusts

Abstract The effect of the dark‐colour‐inducing neurohormone (DCIN = [His7]‐corazonin) of locusts was investigated in field‐collected young and old adults of the grasshopper, Oedipoda miniata (Pallas) (Orthoptera: Acrididae). This species shows homochromy, but neither green‐brown, nor phase‐dependent colour polymorphism. By injecting graded doses of synthetic DCIN in 2 µL of olive oil, young adults were tested within a week of their last moult, and old adults 3.5 months later, a few weeks before natural termination of their reproductive summer diapause. Colour changes were followed for 28 days after injection. Darkening of the young adults was considerable, but their response to DCIN is more moderate than that of conspecific nymphs, by exhibiting a higher threshold, slower response and weaker maximal response. Old adults also show a clear effect, but their response is even slower and less marked than the response of the young adults. It is concluded that the response to DCIN decreases from nymphs to young adults and it is further decreasing with ageing of the adults.

Gall usurpation by the gall-forming aphid, Tetraneura sorini (Insecta Homoptera)

First-instar nymphs of the gall-forming aphid, Tetraneura sorini, frequently usurp incipient galls of its own and other species of Tetraneura by fighting the gall initiator. Fights with conspecific nymphs often escalated. The success of T. sorini in usurping a gall was dependent on the difference in size between the initiator and the invader, and the developmental stage of the gall. Although the probability of success decreased with the development of the gall, T. sorini invaders exhibited a strong preference for the more developed galls. Because of their larger body size, T. sorini nymphs were more successful in usurping incipient galls of other species than of their own species. The tendency in T. sorini to usurp galls may have resulted from their frequent failure to form their own galls. Hypotheses are advanced to explain such gall failure in terms of the interactions between T. sorini and its host plants.