Ability of predatory native Australian fishes to learn to avoid toxic larvae of the introduced toad Bufo marinus

Of two native Australian fishes naïve to the introduced toad Bufo marinus most barramundi Lates calcarifer rapidly learned to avoid B. marinus tadpoles, while sooty grunter Hephaestus fuliginosus exhibited considerable intraspecific variation in their learning ability. Some sooty grunter learned to avoid tadpoles after only a few attacks, while other individuals continued to attack and reject tadpoles throughout the entire laboratory trials. Individuals of both species recognized and avoided tadpoles 1 day after their previous encounter. None of the fishes died during the trials. The observed variation in behavioural responses of fishes to B. marinus may be due to differences in (1) learning ability, (2) fish hunger levels, and or (3) tadpole palatability and toxicity. The results demonstrate that most barramundi and sooty grunter learn to avoid B. marinus tadpoles with minimal trauma. Consequently, it is anticipated that the toads are unlikely to have a significant negative impact on wild populations of these fishes through direct toxic effects.     

Embryo culture of Medicago scutellata and M. sativa

Resistance to the alfalfa weevil (Hypera postica (Gyllenhal)) and the potato leafhopper (Empoasco fabae (Harris)) is lacking in cultivated alfalfa. However, a closely related annual Medicago, Medicago scutellata, possesses dense glandular stem and leaf hairs which provides a mechanism for resistance. Several attempts have been made at transfering the glandular haired traint from M. scutellata to perennial alfalfa with limited success. Earlier studies have shown that one reason for the lack of success is embryo abortion. Therefore, this study was initiated to observe zygotic embryo-genesis and to develop an embryo rescue technique for M. scutellata and M. sativa. Observations of zygotic embryogenesis showed that the two species are similar in morphology and can be described from youngest to oldest as globular, heart, torpedo, and hook shaped embryos. M. sativa embryos are smaller than M. scutellata embryos and develop three to four days later. Self pollinated M. scutellata (PI 307446) and sib mated M. sativa (Saranac AR) embryos were cultivated on Murashige and (2,4-D), indolacetic acid (IAA), 6-benzylaminopurine (BAP), and kinetic (KIN). Embryos from both species were also cultured on Schenk and Hildebrandt's (SH) basal medium with the addition of L-glutamine and L-proline. The experimental design was a completely randomized factorial for each experiment. Heart and torpedo shaped embryos from M. scutellata grew best (27.5% plantlet recovery) when cultured on MS medium with 0.05 mgl^-1 of both IAA and BAP. After 15 to 30 days on this medium, the embryos had only developed shoots. Therefore, it was necessary to transfer the shoots to MS basal medium without phytohormones for rooting. Rooting occurred in 15 to 30 days and the plantlets could be acclimatized to soil within 2 to 4 weeks. M. sativa embryos grew best (31% plantlet recovery) on SH medium with 50 mM L-glutamine. M. sativa embryos developed both shoots and roots on this medium. This information may now be applied to the development of an embryo culture method for recovering insect resistant hybrids between M. scutellata and M. sativa. Disclaimer statement: Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the USDA, and does not imply its approval to the exclusion of other products that may also be suitable.     

Foraging Efficacy of a Larval Parasitoid in a Cotton Patch: Influence of Chemical Cues and Learning

Plant-herbivore chemical signals and behavioral plasticity may enhance parasitoid host-foraging efficacy in the field; however, no studies have quantified the potential benefits from these factors under field-type conditions. The effect of plant-herbivore signals and learning on the foraging efficacy of Microplitis croceipes was quantified by directly observing and recording total and sequential duration of various foraging behaviors relative to 5 randomly placed herbivore-damaged and host-infested cotton plants and 20 undamaged and non-host-infested plants. Microplitis croceipes spent significantly more time searching (flying and antennation) on host infested versus uninfested plants. Antennation time was significantly and negatively correlated with successive host stings. Contrary to expectations of increased duration, flight time remained constant throughout the foraging bout, which may indicate that there was some learning associated with flight. These results suggest that plant-herbivore chemical signals and learning enhances the foraging efficacy of M. croceipes.     

An automated technique for monitoring carbon dioxide respired by insects*

ABSTRACT. A non-dispersive infrared gas analyser equipped with a Luft-type sonic detector and flow-through reference cell was automated to monitor the total volume of carbon dioxide (CO₂) respired by single insects or groups of insects. The infrared analyser was interfaced with an integrator for quantification, a microprocessor to control intermittent air flow through the insect respiration chambers, and a microcomputer for data storage and reduction. This technique has been used to monitor the CO₂ Output of diapausing and non-diapausing mature fifth instar larvae and of developing pupae of the codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae). The resulting data were accurate, quantitative and reproducible.     

Trichome-borne and artificially applied acylsugars of wild tomato deter feeding and oviposition of the leafminer Liriomyza trifolii

Oviposition and adult feeding of the leafminer Liriomyza trifollii (Burgess) (Diptera, Agromyzidae) on Lycopersicon pennellii (Corr.) D'Arcy and its F₁ hybrid with Lycopersicon esculentum (Mill.) was significantly less than that on the cultivated tomato, L. esculentum. The resistance of L. pennellii and the F₁ was reduced following rinsing of foliage with ethanol. Resistant attributes of L. pennellii were transferred to L. esculentum through appression of L. pennellii foliage to L. esculentum leaflets. Application of purified 2,3,4-tri-O-acylglucoses (the principal component of type IV glandular trichome exudate of L. pennellii) to L. esculentum significantly decreased feeding and oviposition on L. esculentum leaflets by 61–99%. Therefore the principal mechanism of resistance to this leafminer by L. pennellii is the secretion of these acylglucoses. Dose response analysis of acylglucoses applied to L. esculentum shows that dosages as low as 10% those found on L. pennellii provide large reductions (91%) in leaf punctures and mines.     

Altered fatty acid composition in regulatory mutants of Streptomyces cinnamonensis

Abstract cDNA-RNA liquid hybridization analysis was used to compare the RNA sequence homology between two members of the Nudaurelia β virus family, Trichoplusia ni virus ( T.ni V) and Dasychira pudibunda virus ( D.p V). Heterologous hybridization experiments demonstrated that these viruses shared little sequence homology. Using oligo(dT) chromatography and oligo(dT)_12–18 as a primer for cDNA synthesis it was shown that neither T.ni V nor D.p V RNA genomes possess a poly(A) tract at the 3' end.