The influence of light and moisture gradients on the attack rate of parasitoids foraging for hosts in a laboratory arena (Hymenoptera: Pteromalidae)

Microhabitat preferences of four parasitoids (Hymenoptera: Pteromalidae) of house fly pupae were measured in a two-dimensional arena containing perpendicular light and moisture gradients. Parasitism by Muscidifurax raptorand Nasonia vitripenniswas greatest in dry substrates, with the latter preferring bright illumination and the former tending to prefer dark. Urolepis rufipesselected bright illumination and moist substrates, attacking the most hosts at bright-moist and dim-moist microhabitats. Spalangia cameroniexhibited no main-effect preference for light intensity or moisture, although parasitism was highest at dim-moist, dark-wet, and dark-moist microhabitats. These results demonstrate that simple abiotic attributes, such as light intensity and substrate moisture concentration, are important in defining some dimensions of the niches of these parasitoids.     

Life history traits and foraging behaviour of Cotesia nonagriae (Olliff) (Hymenoptera: Braconidae), a newly recognised member of the Cotesia flavipes complex of stemborer parasitoids

Cotesia nonagriae (Olliff) from Australia, a parasitoid of the incidental native pest of sugarcane, Bathytricha truncata (Walker) (Lepidoptera: Noctuidae), was previously thought to be a synonym of Cotesia flavipes Cameron. However, recent studies using DNA sequences, morphology and preliminary biological information show that this parasitoid is clearly a different species than C. flavipes and other members of the species complex. Here we further examine differences in the biology of these species by undertaking a detailed study of the life history traits of C. nonagriae , including adult longevity and the potential and realised fecundity of females. In addition, the influence of learning on microhabitat location and foraging behaviour were investigated. Duration of the larval stages and adult longevity of C. nonagriae were longer than previously recorded for other members of the species complex. The potential fecundity of females was similar to C. flavipes (∼200 eggs); however, C. nonagriae oviposited a average of over 100 eggs into each host, almost three times more than for other species in the C. flavipes complex (30–40). The propensity of C. nonagriae to allocate a large number of eggs to each host may be an evolutionary strategy due to the high mortality rate (50–57%) of ovipositing adult wasps. During microhabitat location, both naïve and experienced females demonstrated a strong response towards the plant host complex, with experienced wasps benefiting by having a more rapid response time to host-induced volatiles and cues.     

Life-history and oviposition behaviour of Amitus bennetti, a parasitoid of Bemisia argentifolii

Amitus bennetti Viggiani & Evans (Hymenoptera: Platygasteridae) is a recently described parasitoid of the silverleaf whitefly, Bemisia argentifolii Bellows & Perring (Homoptera: Aleyrodidae). Behaviour and life history of the parasitoid are described. The first nymphal instar of B. argentifolii is preferred by the parasitoid, but the 1st through 4th instar may be parasitised. Females first investigate hosts with their antennae, then walk over the host, and eventually step with their front legs on the leaf and insert their ovipositor inside the host facing away from the host, while the hind legs are still on the host. The time from encounter to oviposition (=latency to oviposition) is shortest on the 1st instar. Oviposition duration (mean=39 s) comprises 50% of the handling time. Development time from egg to adult decreases from 72 days at 15 °C to 42 days at 20 °C to 28 days at 25 °C. We estimate that 400 degree days is required for development, with a development threshold of 10 °C. Adult longevity in the absence of hosts was 29, 26 and 19 days and with hosts present 8, 8 and 5 days at 15, 20 and 25 °C, respectively. Amitus bennetti is proovigenic and oviposits most eggs shortly after adult emergence. During the first day of their adult lives females laid 1, 31 and 49 eggs at 15, 20 and 25 °C, respectively. Compared with other parasitoid species, the development time of A. bennetti is very long, and the implications of this for management of B. argentifolii are discussed.     

Influence of aerial dispersal on persistence and spread of pesticide-resistant Metaseiulus occidentalis in California almond orchards

Aerial dispersal of the phytoseiid Metaseiulus occidentalis (Nesbitt) was evaluated as a component in managing pesticide-resistant populations established in California almond orchards. Peak dispersal occurred in late July and early August during 1982 and 1983. Most predators (and spider mites) left the orchards on the prevailing winds from the northwest. Within the orchard, the prevailing winds had less influence, and dispersal was usually random. Both spider mites and predators dispersed randomly with regard to height from the almond trees, but data obtained during one 24-h interval suggest they do not disperse randomly throughout the day. Most aerial movements occurred between 16–22 h when relative humidity and wind speeds increased and temperatures decreased. Spider mites and predators were trapped on panels located 200 m from the orchard. A survey of carbaryl resistance levels in M. occidentalis collected from almond orchards surrounding the release sites indicates that carbaryl-resistant M. occidentalis dispersed at least 800 m between 1981–83. However, growers wishing to use the resistant strains should release them in their orchards as natural dispersal appears to be too slow. Migration of native M. occidentalis into the release sites appeared to be sufficiently rare that dilution of carbaryl-resistant populations was minimal during a 2–4 year period.

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Résumé La dispersion aérienne du phytoseïdae, M. occidentalis (Nesbitt), a été estimée comme élément de la lutte contre les populations résistantes aux insecticides établies dans les vergers de Californie. La dispersion maximale s'est produite fin juillet et début a oût en 1982 et 1983. La plupart des prédateurs (et des acariens) quittent les vergers avec les vents dominants du nordouest. Dans le verger, les vents dominants sont moins importants et la dispersion est généralement au hasard. Tant les acariens que les prédateurs se dispersaient au hasard par rapport à la taille des amandiers, mais les relevés sur 24 heures laissent supposer qu'il n'y a pas une distribution aléatoire pendant la journée. La plupart des mouvements aériens se produisirent entre 16 et 22 heures quand HR et vitesse du vent augmentaient et température diminuait. Les acariens et prédateurs ont été piégés sur des panneaux à 200 m du verger.