Henrik F. Brødsgaard

The predatory mite Hypoaspis miles: biological and demographic characteristics on two prey species, the mushroom sciarid fly, Lycoriella solani, and the mould mite, Tyrophagus putrescentiae

The biology of Hypoaspis miles Berlese (Acarina: Hypoaspidae) fed on mushroom sciarid larvae (Lycoriella solani Winnertz) (Diptera: Lycoriidae) and mould mites (Tyrophagus putrescentiae Schrank) (Acari: Acaridae), was investigated by laboratory experiments at 20 °C, 75% r.h. and LD16:D8 hours. H. miles had a significantly shorter development time and a significantly lower juvenile mortality when fed on sciarid larvae than on mould mites, the development time being 14.5 days and the mortality 3.5% on the former prey. The preoviposition and postoviposition periods of H. miles were not uninfluenced by the prey species and were 5–9 and 32–37 days, respectively. Oviposition periods of 53.2 and 68.5 days and female longevities of 82 and 109.6 days were observed on diets of sciarid larvae and mould mites, respectively. Male longevity (168–219 days) was uninfluenced by the prey species. The egg production of H. miles on sciarid larvae was estimated to be 44.4 ± 4.33 eggs per female, as compared to 22.43 ± 1.79 eggs per female on mould mites. The sex‐ratio of the offspring was significantly influenced by the prey species, the ratios (♀/(♀+♂)) being 0.66 on sciarid larvae and 0.54 on mould mites. The net reproductive rate (R0) for H. miles fed on sciarid larvae was approximately 27 which was three times higher than for mites feeding on mould mites. The innate capacity of increase (rm) was highest (0.0747 day−1) when sciarid larvae served as food, giving a doubling time of 9.3 days as compared to 12.8 days on mould mites. The generation times were 44.28 on sciarid larvae and 40.67 days on mould mites. The daily food consumption rate of juvenile and adult H. miles was 0.24 and 0.86 sciarid larvae and 10.8 and 21.7 mould mites, respectively. In terms of weight consumed, however, the consumption of sciarid larvae was 2–3.5 times the weight of mould mites. The ratio of females to males influenced the oviposition period and egg production of H. miles, with virgin females laying fewer eggs over a longer period of time as compared with females with access to males. The egg production in relation to the sex‐ratio was described by models predicting a maximum number of eggs per female of 22.3 to be attained at a sex ratio of 0.69 (♀/(♀+♂)) and a maximum daily number of eggs per female of 0.33 to be attained at a sex ratio of 0.37 (♀/(♀+♂)).

Life table characteristics of Macrolophus caliginosus preying upon Tetranychus urticae

The life table characteristics of the polyphagous mirid Macrolophus caliginosus Wagner (Heteroptera: Miridae) preying on various stages of Tetranychus urticae Koch (Acari: Tetranychidae) with tomato as host plant were described at 22 °C. The following average parameters were obtained: Female longevity: 28.7 days; fecundity: 0.7 eggs/female/day; egg mortality: 2.6%; pre‐oviposition period: 5.5 days; oviposition period: 18.1 days; post‐oviposition period: 3.2 days; juvenile development time: 26.8 days; juvenile mortality: 34.9%; and sex ratio (♀/(♀+♂)) 0.46. Life table parameters were estimated as net reproduction rate (R0): 6.15; intrinsic rate of increase (rm): 0.031 day−1; finite rate of increase (≤): 1.032; mean generation time (Tc): 58.17 days; and doubling time (T2) 22.2 days. The parameters obtained were in accordance with those reported for M. caliginosus fed on another mite species (T. turkestani Ugarov & Nikolski (Acari: Tetranychidae)). However, compared to the performance of M. caliginosus fed on common glasshouse insect pests, a diet consisting of only mites appeared to be inferior. However, being a voracious predator, M. caliginosus may be a valuable addition to existing methods of mite control.

Macrolophus caliginosus: Functional response to whiteflies and preference and switching capacity between whiteflies and spider mites

Laboratory experiments were performed with adult female Macrolophus caliginosus Wagner (Heteroptera: Miridae) at 22°C on bean plants to determine the functional response towards whiteflies, as well as the preference and switching capacity between the two prey species: whiteflies and spider mites. Predation of females presented with first instars of Trialeurodes vaporariorum Westwood (Homoptera: Aleyrodidae) was of a Type III functional response. The observed maximum predation was approximately 75 first instars at high prey densities within a 24‐h period. The preference of M. caliginosus females between eggs of T. vaporariorum and Tetranychus urticae Koch (Acarina: Tetranychidae) changed with the ratio of offered prey. The preference for T. vaporariorum eggs increased non‐linearly with increasing proportions of this prey type. The average maximum predation of whitefly and spider mite eggs were approximately 166 and 111 eggs per day, respectively, at the highest ratio of the two preys. The proportion of M. caliginosus females found on the test plants at the end of the experiment increased with prey density suggesting that this mirid spends more time in areas with high prey density. Macrolophus caliginosus females are voracious predators of eggs and first instars of T. vaporariorum as well as of spider mite eggs and may thus be a valuable addition to existing methods of biological control of T. vaporariorum and T. urticae.

Host plant effects on the functional response of Neoseiulus cucumeris to onion thrips larvae

Abstract:  The performance of herbivores, natural enemies and their interactions may be affected directly or indirectly by host plant traits, e.g. the physical plant characteristics may influence the search pattern and the functional response of predators. We studied the functional response of adult females of the predatory mite Neoseiulus cucumeris to first instar larvae of Thrips tabaci on three host plants (sweet pepper, eggplant and cucumber). The 24‐h leaf disc experiments conducted at 25 ± 1°C, 60 ± 10% relative humidity and 16 : 8 h (light : dark) showed that N. cucumeris exhibited a type II functional response on all host plants. The following search rates and handling times were estimated from fitting the data to the disc equation 0.043/h and 1.798 h (cucumber); 0.048/h and 1.030 h (sweet pepper) and 0.0441/h and 2.294 h (eggplant) giving an estimated maximum predation of 13.35, 23.31 and 10.46 larvae per day respectively. The data from sweet pepper could also be described by the random predator equation (a′: 0.051/h; Th: 0.472 h). The host plant species interacted significantly with prey density on the functional response of N. cucumeris with the relative differences in the number of thrips eaten on each host plant increasing with density. It is suggested that it is mainly the difference in trichome density between the three host plants that is responsible for the observed differences in the functional response of N. cucumeris. These results emphasize the importance of the host plant characteristics on the performance of natural enemies and for optimizing their use in biological control of pests.

Two Anthocoris bugs as predators of glasshouse aphids – voracity and prey preference

Voracity and prey preference were evaluated for adult females of the predatory bugs Anthocoris nemorum (L.) and Anthocoris nemoralis (Fabricius) (Heteroptera: Anthocoridae) preying upon five species of aphids (Homoptera: Aphididae), of which Myzus persicae Sulzer, Aulacorthum solani (Kaltenbach), Macrosiphum euphorbiae (Thomas), and Aphis gossypii Glover are common pests in Danish glasshouse crops. Aphis fabae Scopoli was included to determine the influence of food quality on the preference of the predators, since A. fabae has proved to be of poor nutritional value to Anthocoris spp. The experiments were carried out over 24 h in climate cabinets at 20 °C, 60–70% r.h., L18:D6. The aphids were offered in equal amounts in combinations of two species in instars of comparable size. Myzus persicae served as a reference species in all combinations. Both predators accepted all five species of aphids as prey. The numbers of aphids killed per 24 h period varied between 3.7 and 18.0 for A. nemorum and between 3.6 and 12.7 for A. nemoralis. Field collected A. nemorum females, presumably in a state of reproductive diapause, killed in three of four prey combinations significantly more aphids than did ovipositing A. nemoralis females which originated from a commercial rearing. When A. nemorum females had terminated their reproductive diapause and commenced oviposition, voracity increased approximately threefold. When prey preferences were evaluated as a total number of killed prey, no difference in preference was found between the two Anthocoris species. Both predatory bugs preferred M. persicae to the other species, the most accepted alternative prey were A. gossypii, A. fabae, A. solani, and M. euphorbiae, in descending order. However, evaluating preference by number of aphids consumed, A. nemoralis showed a more pronounced preference for M. persicae, especially when combined with A. fabae. In nearly every case, A. nemoralis rejected A. fabae as a food item after killing the aphid. Thus, A. nemoralis exhibited a more specific food choice than A. nemorum. By killing and consuming different aphid species found in glasshouse crops – particularly M. persicae– both A. nemorum and A. nemoralis showed preliminary qualities as agents for the biological control of aphids.

Odour-mediated responses of a predatory mirid bug and its prey, the two-spotted spider mite

It has been shown that many natural enemies of herbivorous arthropods use herbivore induced plant volatiles (HIPVs) to locate their prey. Herbivores can also exploit cues emitted by plants infested with heterospecifics or conspecifics. A study was conducted to test whether green bean HIPVs as well as odours emitted directly by spider mites influenced the orientation behaviour of the predatory mirid bug, Macrolophus caliginosus and its prey, Tetranychus urticae in a Y-tube olfactometer. Our results show that both spider mites and M. caliginosus preferred spider mite infested green bean plants to uninfested plants. For M. caliginosus this response was mediated by HIPVs whereas for T. urticae it was mediated through a composite response to both HIPVs and odours emitted directly by the conspecifics (and their associated products). The results may be of use in practical biocontrol situations, through e.g., plant breeding for improved HIPV production, conditioning of mass-reared predators to appropriate cues, and employment of “push–pull-strategies” by using HIPVs.

Males of the predatory mirid bug Macrolophus caliginosus exploit plant volatiles induced by conspecifics as a sexual synomone

The olfactory responses of male and female Macrolophus caliginosus Wagner (Heteroptera: Miridae) adults towards volatiles from green bean plants previously exposed to feeding by conspecifics and to direct odours from conspecifics were tested in a Y‐tube olfactometer. Female M. caliginosus did not respond to volatiles from plants exposed to mirid feeding or to odours emitted directly by adult mirids. In contrast, male mirid bugs were attracted both to volatiles from plants previously exposed to feeding by conspecific females and to odours emitted by conspecifics only with a marginally significant preference for the former. The gas chromatography‐mass spectrometry analysis showed that mirid feeding induced the release of 11 additional compounds as compared to the volatiles emitted from clean plants. Three of these substances (5‐ethyl‐2(5H)‐furanone, Z‐3‐hexenyl tiglate, and E,E‐α‐farnesene) were released only after feeding by females. Furthermore, 21 compounds were identified in volatiles emitted directly by mirids, 12 of which were unique to the mirids (i.e., not present in clean plants or plants previously exposed to mirid feeding). The results suggest that female‐specific herbivore‐induced plant volatiles play a role as mate‐finding cues by the male mirids. The ecological implications of the findings are discussed, and the term ‘sexual synomone’ is introduced.

Interactions Between Two Polyphagous Predators, Orius majusculus (Hemiptera: Anthocoridae) and Macrolophus caliginosus (Heteroptera: Miridae)

The mutual predation between two polyphagous predators, Orius majusculus (Reuter) (Hemiptera, Anthocoridae) and Macrolophus caliginosus Wagner (Heteroptera: Miridae), was examined in laboratory experiments with and without presence of Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae). Adults of O. majusculus preyed upon M. caliginosus in the absence and in some circumstances also in the presence of F. occidentalis, whereas neither nymphs nor adults of M. caliginosus preyed upon O. majusculus. Orius majusculus nymphs did not prey upon M. caliginosus. The predation of O. majusculus on F. occidentalis was unaffected by the presence of M. caliginosus suggesting that the presence of this mirid will not hamper biological control of F. occidentalis.

Intraguild predation by Anthocoris nemorum (Heteroptera: Anthocoridae) on the aphid parasitoid Aphidius colemani (Hhymenoptera: Braconidae)

The magnitude of intraguild predation by adult females of the predator Anthocoris nemorum on immature larvae of the aphid parasitoid Aphidius colemani inside mummies of peach-potato aphids Myzus persicae was investigated under laboratory conditions in a preference experiment. Each predator consumed a mean (95% confidence limits) of 2.8 (2.1; 3.8) immature parasitoids within mummies and 3.6 (2.7; 4.6) unparasitised aphid nymphs. Thereby A. nemorum engaged in intraguild predation with A. colemani and did not exhibit prey preference between mummies and unparasitised aphids.

Odour‐mediated preference and prey preference of Macrolophus caliginosus between spider mites and green peach aphids

Abstract  A comparative study between direct prey preference and odour‐mediated preference of the predatory mirid bug, Macrolophus caliginosus, was conducted. We used a Y‐tube olfactometer to determine the attraction of the predator to herbivore‐induced volatiles from Myzus persicae or Tetranychus urticae‐infested sweet pepper plants over clean plants and to direct prey odours over clean air. The mirid bugs showed a stronger response to odours from infested plants than to odours from clean plants. The mirids did, however, not seem to exploit odours emitted directly from the prey themselves. Our results further demonstrated that M. caliginosus prefers M. persicae to T. urticae in a direct two‐choice consumption test. This preference was, however, not reflected in a similar odour‐mediated preference between plant volatiles induced by either of the two preys. Two hypotheses are suggested for this neutral response of the mirids to herbivore‐induced volatiles from a preference prey or a non‐preference prey.