We investigated the ability of females of the aphidophagous chrysopids Chrysopa oculata and Chrysopa perla to distinguish clean substrates from substrates with tracks of chrysopid first instars after ablation of various sensory organs potentially involved in the detection of oviposition-deterring semiochemicals (ODSCs). Also studied were effects of storage time on the degree of oviposition deterrence of substrates contaminated by larvae and by extracts of ODSC in intact females. C. oculata and C. perla laid significantly fewer eggs on substrates with conspecific larval tracks than on simultaneously provided clean substrates. Females of both chrysopids could perceive ODSCs solely through sense organs on the head. The oviposition of each species was significantly lower on contaminated than on clean substrates when any kind of sense organ on the head was completely removed, i.e. antennae, maxillary palpi, or labial palpi. C. oculata could still effectively differentiate substrates after ablation of both maxillary and labial palpi, indicating possible detection of volatiles via the antennae during flight. Only if all three pairs of sensory appendages were removed did females lay similar numbers of eggs on both substrates. In contrast, C. perla laid similar numbers of eggs on clean substrates and substrates with either conspecific or C. oculata larval tracks when maxillary and labial palpi were removed. Substrates with tracks of first instars of C. perla deterred C. oculata from oviposition after one year and conspecific females after 1.5 years from contamination. Both species laid significantly fewer eggs on substrates with tracks of C. oculata first instars than on clean substrates even after three years. Tracks of C. oculata third instars did not deter conspecific females more than tracks of first instars. ODSCs from tracks were easily extracted with water. Thus, precipitation is likely to reduce deterrent effects of contaminated plants. Chloroform extract from C. oculata first instars strongly deterred conspecific females from oviposition. Even after 725 days of storage, we found no statistically significant decline in the effect. The extract could be used to redirect egg laying from constructional parts of rearing cages to exchangeable oviposition substrates in mass rearing of chrysopids used for biological control. The hexane extract of third instars was inactive.
Larvae of Aphidoletes aphidimyza (Rondani) (Diptera: Cecidomyiidae) secrete an oviposition-deterring pheromone (ODP). In choice tests, females of A. aphidimyza laid significantly fewer eggs on Vicia faba L. plants infested with Aphis fabae Scopoli (Homoptera: Aphidoidea) that were previously exposed to conspecific third-instar larvae or a water extract of their ODP.
A. aphidimyza females also laid fewer eggs on aphid-infested plants that were previously exposed to unfed first-instar larvae of Chrysopa oculata Say, Chrysopa perla (L.) or Chrysoperla carnea (Stephens) (Neuroptera: Chrysopidae), or second-instar larvae of Coccinella septempunctata L. (Coleoptera: Coccinellidae). However, the response to traces of C. carnea larvae was very weak.
Females of species predatory as adults, Chrysopa commata Kis & Ujhelyi, C. oculata Say and C. perla (L.), and also species not predatory as adults, Chrysoperla carnea (Stephens), laid more eggs on clean substrates, than on those exposed previously to conspecific or heterospecific first-instar larvae. Substrates contaminated with oviposition-deterring allomones (ODAs) deterred females of C. oculata most. On the average the deterrent effects of substrates contaminated by larvae of C. oculata or C. perla were greater than those contaminated by C. carnea or C. commata. Results indicate that both intra-and interspecific responses to ODA occur in chrysopids and may enable them to distribute their larvae more uniformly between prey patches.
The effects of oviposition-deterring larval tracks of four aphidophagous coccinellids and two chrysopids were investigated on females of four coccinellid species in choice tests. Aphidophagous coccinellids Cycloneda limbifer Casey, Semiadalia undecimnotata (Schneider) and Coccinella septempunctata L. laid significantly fewer eggs on sites with tracks of unfed conspecific first instar larvae than on clean sites, but Leis dimidiata (F.) laid similar numbers of eggs on both sites.
In some but not all species, tracks of heterospecific predators also deterred coccinellid females. Interspecific effects were stronger between some allopatric species than between the sympatric coccinellids C. septempunctata and S. undecimnotata. C. limbifer laid relatively few eggs on sites previously exposed to larvae of S. undecimnotata and L. dimidiata. S. undecimnotata avoided sites with tracks of L. dimidiata larvae. The two smaller species, C. limbifer and S. undecimnotata, laid considerably fewer eggs per batch than the larger coccinellids, C. septempunctata and L. dimidiata. C. limbifer and S. undecimnotata oviposited similar numbers of eggs on clean sites and sites with tracks of chrysopid larvae of the species Chrysopa oculata and Chrysopa perla. Females of C. septempunctata laid fewer eggs on sites previously exposed to larvae of C. oculata but not C. perla.
Densities of faecal spots of coccinellid females on clean substrates and substrates with tracks of predatory larvae differed significantly in only one choice test (C. limbifer females exposed to tracks of S. undecimnotata larvae). This indicates that the presence of larval tracks affects where females lay eggs more than where they search.
The persistence of oviposition-deterring effects of coccinellid and chrysopid larval tracks on females of three aphidophagous coccinellid species was compared. One month old tracks of first instars of the coccinellid Cycloneda limbifer Casey deterred conspecific females from oviposition in choice tests with clean and contaminated substrates. Intraspecific effect of larval tracks in Semiadalia undecimnotata Schneider was statistically significant after 10 days. Although fresh tracks of conspecific first instars effectively deterred females in both tested populations of Coccinella septempunctata L., deterrent effects disappeared when tracks of larvae were only one day old. However, females of C. septempunctata laid fewer eggs on sites with 10 days old tracks of Chrysopa oculata Say or sites with one month old tracks of Chrysopa perla (L.) first instars than on clean sites. In contrast to females of C. septempunctata and S. undecimnotata, C. limbifer females left significantly more faecal spots on clean sites than on sites with 5-30 days old tracks of conspecific first instars. This indicates that sites with tracks of larvae can also effectively repel conspecific females of some coccinellid species from searching.
Choice tests showed that tracks left by coccinellid larvae have generally little effect on oviposition site selection by chrysopid females. Fresh tracks of first instar larvae of the coccinellid species Coccinella septempunctata, Cycloneda limbifer, Leis dimidiata and Semiadalia undecimnotata, did not deter females of the chrysopid Chrysopa oculata from laying eggs. Females of Chrysopa perla avoided ovipositing only on substrates with tracks of L. dimidiata larvae.