Showing papers on "Lasius published in 1996"

Wax covers in larvae of two Scymnus species: do they enhance coccinellid larval survival?

Abstract: We tested the protective function of larval wax covers in the two ladybird beetle species, Scymnus nigrinus and S. interruptus, against cannibalism, predation and ant aggression, and its importance for the distribution of both species in the field. Cannibalism was generally very low and not influenced by the presence or absence of the wax cover, or by larval size. Fourth-instar larvae of three ladybird species, Adalia bipuncata, Exochomus quadripustulatus and Harmonia quadripunctata, consumed Scymnus larvae-which are much smaller-regularly, independent of the presence or absence of waxes. By contrast, first-instar larvae of the three species had generally little success when attacking Scymnus spp. larvae. Wax-covered S. interruptus larvae survived significantly more attacks by the predacious carabid beetle Platynus dorsalis than larvae without wax cover. Wax-covered S. interruptus larvae and S. nigrinus larvae survived attacks by workers of the ant species, Lasius niger and Formica polyctena, respectively, significantly more often than larvae without wax covers. We show that, in the field, Scymnus larvae have higher densites in ant-attended resources than in unattended ones and conclude that both Scymnus species benefit from the ability to feed in ant-attended aphid colonies by a reduced predation risk.

The consequences of ant-attendance to the biological control of the red wax scale insect Ceroplastes rubens by Anicetus beneficus

Abstract: The effects of an attendant ant (Lasius niger) on the host-parasitoid system of the red wax scale insect (Ceroplastes rubens) and its parasitoid wasp (Anicetus beneficus) and in relation to biological control efficiency of the wasp were examined by behavioural field observations, ant exclusion experiments in the field, and field censuses of the host population density and the percentage of parasitism. Parasitoids were frequently observed to interrupt their ovipositional behaviour due to interactions with ants attending host aggregations. Ant-exclusion experiments revealed that ant-attendance caused a decrease in the percentage parasitism and consequently an increase in the growth rate of the host population. The results of field censuses showed that, under the natural conditions in which some generalist ant species usually attended the host aggregations, host density remained at a high level or gradually increased over a 5-year period. Inverse density dependence was detected in the parasitism, which was expected from the density-biased defensive effects of ant-attendance. Overall, these results indicate that ant-attendance on C. rubens restricts the ovipositional ability of the parasitoid and thus reduces the effectiveness of the parasitoid as a control agent of C. rubens.

Behavioral strategies of aphid hyperparasitoids to escape aggression by honeydew-collecting ants

Abstract: We analyzed the behavioral interactions between two species of honeydew-collecting ants (Lasius niger, Myrmica laevinodis) and foraging females of four species of aphid hyperparasitoids (Aphidencyrtus aphidivorus, Dendrocerus carpenteri, Pachyneuron aphidis, Asaphes vulgaris) usingAphis fabae ssp.cirsiiacanthoidis andLysiphlebus cardui on thistles as aphid and primary parasitoid, respectively. The observed interaction patterns and foraging parameters varied within hyperparasitoid species and revealed different strategies based upon behavioral and morphological constraints.D. carpenteri generally tried to avoid ant encounters. This avoidance strategy was successful in interactions withM. laevinodis but failed when encountering the more aggressiveL. niger, which caused about 26% adult mortality. In contrast,A. aphidivorus, P. aphidis, andA. vulgaris possess jumping ability and were hardly exposed to mortality risks. The escape reaction “jump off” was used as soon as ants made physical contact with foraging females. While the flight strategy ofP. aphidis is connected with cryptic movement patterns without avoidance behavior,A. aphidivorus first avoided ants and jumped off only as a last resort. Similar patterns, but less expressive, are displayed byA. vulgaris. We suggest that these different strategies are responsible for different foraging success in ant-attended resources in field.

Chemical and tactile communication between the root aphid parasitoid Paralipsis enervis and trophobiotic ants : consequences for parasitoid survival

Abstract: Females of the aphid parasitoidParalipsis enervis received liquid food by regurgitation (trophallaxis) from workers of the ant speciesLasius niger, but were not fed by workers ofMyrmica laevinodis andTetramorium caespitum. WhileP. enervis was not treated aggressively by workers of any of these species,Lasius flavus workers killed the parasitoid. This different ant behaviour resulted in a different parasitoid longevity. WhileP. enervis survived for only 10 min in the presence ofL. flavus (due to ant aggression) or for approximately one day in the presence ofT. caespitum andM. laevinodis (due to lack of trophallaxis), survival increased significantly to more than five days in the presence ofL. niger, which provided food regularly to the parasitoids. Our study suggests thatP. enervis mimics behavioural signals ofL. niger, as well as odor cues of its host aphidAnoecia corni, to avoid aggression byL. niger.

Prey composition of three Dipoena species(Araneae: Theridiidae)specializing on ants.

Abstract: We examined species and size compositions of prey in the three Dipoena spiders specializing on ants. Dipoena punctisparsa fed exclusively on small ants, Lasius. In this spider, the number of prey fed at a time increased with the spider body size. Dipoena castrata mainly captured Componotus and Lasius, and most spiders fed on a single prey. The body size of prey fed upon by this species increased with the spider size. Dipoena mustelina captured a variety of ant species, ranging from very small to large ones.

A test method for field studies of insecticidal bait formulations against the ant lasius niger (hymenoptera: formicidae)

Abstract: In the early spring Lasius niger may be a nuisance indoors. These ants often originate from nests right next to the foundation, below the house or sometimes even directly under the flo.or. The ants raise the humidity, which may result in severe damage to the woodwork, due to rot. The same applies to an even greater extent to other species: L. umbratus and L. juliginosus. The present method was developed for the evaluation of insecticidal bait formulations in the field. Special emphasis was put on maintaining the colony members' ability to communicate mutually. The study evaluated the response of L. niger to seven bait formulations, five containing azamethiphos, one containing chlorpyrifos, and a reference with no insecticide. The primary interest of the experiment was to develop a method where the palatability of the bait formulations, the ability of the baits to attract L. niger, and the ants' acceptance of the baits could be investigated. Thirty-four ant nests were used. When the number of ants on a jam bait indicated high activity, the test was initiated. A new jam bait was put into position for fifteen minutes and then replaced by the test bait for fifteen minutes. This was repeated three times. The number of ants visiting each bait was counted, and a small portion was collected by a sucking device when leaving the bait. The latter was observed for up to 24 hours to estimate the mortality. The results with the reference bait showed that the ants were only slightly affected by the method, while the palatability of the test baits ranged from as good as the controls to complete repellence. This result was confirmed by the percentage of ants killed. And both results indicate that the method could be used to establish comparable data for the efficacy of ant baits.