Alan Gunn

Baculovirus resistance in the noctuid Spodoptera exempta is phenotypically plastic and responds to population density

Parasite resistance mechanisms can be costly to maintain. We would therefore predict that organisms should invest in resistance only when it is likely to be required. Insects that show density–dependent phase polyphenism, developing different phenotypes at high and low population densities, have the opportunity to match their levels of investment in resistance with the likelihood of exposure to pathogens. As high population densities often precipitate disease epidemics, the high–density form should be selected to invest relatively more in resistance. We tested this prediction in larvae of the noctuid Spodoptera exempta. Larvae reared at a high density were found to be considerably more resistant to a nuclear polyhedrosis virus than those reared in isolation. A conspicuous feature of the high–density phase of S. exempta and other phase–polyphenic Lepidoptera is cuticular melanization. As melanization is controlled by the phenoloxidase enzyme system, which is also involved in the immune response, this suggests a possible mechanism for increased resistance at high population densities. We demonstrated that melanized S. exempta larvae were more resistant than non–melanized forms, independent of rearing density. We also found that haemolymph phenoloxidase activity was correlated with cuticular melanization, providing further evidence for a link between melanization and immunity. These results suggest that pathogen resistance in S. exempta is phenotypically plastic, and that the melanized cuticles characteristic of the high–density form may be indicative of a more active immune system.

The determination of larval phase coloration in the African armyworm, Spodoptera exempta and its consequences for thermoregulation and protection from UV light

Spodoptera exempta exhibits a density‐dependent phase polyphenism in which caterpillars reared in isolation (phase solitaria) tend to be green/brown and cryptic while those reared in groups (phase gregaria) are black and highly visible. Differences in coloration between solitaria and gregaria phase larvae become apparent in the third instar and are pronounced by the final instar. Larval rearing densities as low as two larvae per 250 ml container are sufficient to induce gregaria coloration in 61% of the insects and at higher densities this is the only coloration expressed. Larvae transferred from isolated to crowded conditions or vice versa tend to retain or adopt gregaria phase coloration which suggests that this is highly advantageous. Black coloration is also induced in single larvae reared with other species of caterpillar (S. littoralis). Isolated larvae reared at low temperature tend to become melanic while crowded larvae reared at high temperature tend to be less melanised although they do not adopt the solitaria phase coloration. These results suggest that phase coloration is determined by non species‐specific inter‐larval contact, although it can be modulated by temperature. Under laboratory conditions, gregaria phase larvae heat up faster than solitaria; this is partially a consequence of their black coloration but their smaller size is a more important factor. The cuticles of the gregaria larvae absorb significantly more ultraviolet radiation than those of solitaria but this does not confer any protection when larvae are irradiated at 254 nm.

The ability of the blowflies Calliphora vomitoria (Linnaeus), Calliphora vicina (Rob-Desvoidy) and Lucilia sericata (Meigen) (Diptera: Calliphoridae) and the muscid flies Muscina stabulans (Fallén) and Muscina prolapsa (Harris) (Diptera: Muscidae) to colonise buried remains.

The blowflies Calliphora vomitoria (Linnaeus), Calliphora vicina (Rob-Desvoidy) and Lucilia sericata (Meigen) exhibited a limited ability to colonise pig liver baits buried in loose soil. Calliphora vomitoria colonised baits buried at 5 cm but no deeper whilst C. vicina and L. sericata colonised remains at 10 cm but not at 20 cm. The baits were colonised by larvae hatching from eggs laid on the surface of the soil. Both C. vomitoria and L. sericata were able to develop from eggs through to adulthood on baits that were infested before being buried and the larvae developed at similar rates and pupariated at similar depths to larvae developing on baits on the soil surface. The muscid flies Muscina stabulans (Fallén) and Muscina prolapsa (Harris) colonised remains buried in loose soil at a depth of 40 cm and even when presented with baits on the soil surface their larvae tended to remain in the soil beneath the baits. In compacted soil, M. stabulans colonised baits buried at 10 cm but M. prolapsa only colonised those buried at 5 cm. In both muscid species, the adult flies were instantly attracted to feed on fresh blood and laid eggs in the soil above buried baits within 30min of them being introduced into the cages. The adult muscid flies did not attempt to burrow into the soil and their larvae colonised the baits from eggs laid on the soil surface. This information could be useful in determining whether a body was stored above ground before being buried and/or the time since burial occurred.

Inter-host transfer and survival of Varroa jacobsoni under simulated and natural winter conditions

SUMMARYVarroa jacobsoni transferred between living bees and from dead and dying bees on to living bees under both natural and laboratory-simulated winter cluster temperatures. In trials involving 261 bees and 161 mites, 26% of the mites moved from one live host to another within 7 days. When an infested bee was dead or dying, up to 75% of the mites would transfer to a live bee within 24 h. When their host died, mites would remain on the dead bee, provided an alternative bee was not available, for an average of 48 ± 26.5 h before dismounting. During this time they continued to feed and exhibited behaviour which would enhance their chances of transfer to a new host. These results question previous suggestions that V. jacobsoni seldom moves between hosts during overwintering and that the majority of them would inevitably die with their host. This has important consequences for models of varroa population dynamics and implications for the transmission of pathogens between bees by the mites.

Antimicrobial properties of mucus from the brown garden snail Helix aspersa

Abstract Research into naturally occurring antimicrobial substances has yielded effective treatments. One area of interest is peptides and proteins produced by invertebrates as part of their defence system, including the contents of mollusc mucus. Mucus produced by the African giant land snail, Achatina fulica has been reported to contain two proteins with broad-spectrum antibacterial activity. Mucus from the brown garden snail, Helix aspersa, appears to have skin regeneration properties. This study sought to investigate the antimicrobial properties of H. aspersa mucus. Mucus was collected from H. aspersa snails, diluted in phosphate-buffered saline (PBS), with the supernatant tested against a wide range of organisms in a disc-diffusion antimicrobial assay. This was followed with comparative experiments involving A. fulica, including bacteriophage assays. Mucus from both species of snail was passed through a series of protein size separation columns in order to determine the approximate size of the antimicrobial substance. Electrophoresis was also carried out on the H. aspersa mucus. Results indicated that H. aspersa mucus had a strong antibacterial effect against several strains of Pseudomonas aeruginosa and a weak effect against Staphylococcus aureus. Mucus from A. fulica also inhibited the growth of S. aureus, but the broad spectrum of activity reported by other workers was not observed. Antimicrobial activity was not caused by bacteriophage. Size separation experiments indicated that the antimicrobial substance(s) in H. aspersa were between 30 and 100 kDa. Electrophoresis revealed two proteins in this region (30–40 kDa and 50–60 kDa). These do not correspond with antimicrobial proteins previously reported in A. fulica. This study found one or more novel antimicrobial agents in H. aspersa mucus, with a strong effect against P. aeruginosa.

The effectiveness of computer-based teaching packages in supporting student learning of parasitology

Abstract The usefulness of providing students with information via electronic notes, a website and a self-assessment quiz was assessed in three ways. Students’ perceptions of each package were gauged through questionnaires; their patterns of use of the electronic support was monitored via the computer system and the effect of provision of these materials on performance was measured by marks in the end of module examination. The results clearly showed that computer-assisted learning packages are at least as effective in imparting information as traditional lectures and that students value the opportunity to reinforce their learning through interactive lecture notes and self-assessment quizzes. However, students definitely expressed the opinion that they would not like to have too much of their lecture time replaced by computer packages and they seemed to require the option of ‘downloading’ the information onto a piece of paper for individual use. Therefore, it seems that the teachers who are seeking new ways to teach students must avoid overuse of computer-based packages and use other forms of student-directed learning, such as problem-based tutorials, as well. Also, they should include at least as much contact time with students as in a formal lecture programme if they are to support learning effectively.

The value of computer based formative assessment in undergraduate biological science teaching

Abstract The impact of introducing computer-based self-assessment quizzes on examination performance was monitored in 5 modules delivered to undergraduate students in the first, second, and final years at university over a 2–3 year period. The patterns of usage were also monitored to determine the extent to which the quizzes were used and whether there were differences between the students at different stages of their education. Overall, all groups used the CBA package in broadly similar ways, although year 1 students were least likely to access their quiz. Most students used the quizzes during normal ‘office hours’ between Monday and Friday, but up to 22% of use occurred in the evenings and 3–20% at weekends. Most log-on events were recorded in the weeks immediately prior to an examination. There was a positive relationship between the introduction of the quizzes and mean examination mark; in particular, increases in the proportion of students obtaining good (>60%) marks were observed. The results suggest that the provision of computer-based self-assessment quizzes is helpful to students and that the opportunity to access them at any time is appreciated. At present, it appears that the more motivated individuals are assisted most by the quizzes. Integration of formative CBA into a programme of learning appears to be beneficial, particularly when used in conjunction with other forms of formative assessment.

The colonisation of remains by the muscid flies Muscina stabulans (Fallén) and Muscina prolapsa (Harris) (Diptera: Muscidae).

In the field, the muscid flies Muscina stabulans (Fallén) and Muscina prolapsa (Harris) only colonised buried baits in June, July and August. The two-species co-occurred on baits buried at 5cm but only M. prolapsa colonised baits buried at 10cm. Other species of insect were seldom recovered from buried baits regardless of the presence or absence of Muscina larvae. In the laboratory, both M. stabulans and M. prolapsa preferentially colonised liver baits on the soil surface compared to those buried at 5cm. Baits buried in dry soil were not colonised by either species whilst waterlogged soil severely reduced colonisation but did not prevent it entirely. Dry liver presented on the soil surface was colonised and supported growth to adulthood but if there was no surrounding medium in which the larvae could burrow then they died within 24h. M. stabulans showed a consistent preference for ovipositing on decaying liver rather than fresh liver, even when it had decayed for 41 days. The results for M. prolapsa were more variable but it was also capable of developing on both fresh and very decayed remains. Blood-soaked soil and dead slugs and snails stimulated egg-laying by both species and supported larval growth to adulthood. Mushrooms, melon, and bananas also stimulated egg-laying although to a much lesser extent and very few larvae survived to adulthood. Horse faeces stimulated extensive egg-laying but the larvae invariably died during the first or second instar and none survived to pupariation. This information could be useful when determining the forensic significance of Muscina larvae recovered from dead bodies.

Moniezia expansa : the interproglottidal glands and their Secretions

Acetylcholinesterase (EC 3:1:1:7) and alkaline phosphatase (EC 3:1:3:1) were detected in secretions of Moniezia expansa maintained in vitro. Ultrastructural cytochemical studies demonstrated acetylcholinesterase activity on the surface of the microtriches at the base of the interproglittidal glands and in the gland lumen but not in the distal tegument or the gland cells. Alkaline phosphatase activity was demonstrated in the cytoplasm of the gland cells and especially in their protoplasmic connections with the distal tegument. Activity was also found in the distal tegument and the microtriches. It is suggested that the acetylcholinesterase secreted by M. expansa performs a metabolic role at the worms surface.

The exploitation of fresh remains by Dermestes maculatus De Geer (Coleoptera, Dermestidae) and their ability to cause a localised and prolonged increase in temperature above ambient

This article discusses the ability of adults of the coleopteran beetle Dermestes maculatus (De Geer) to colonise fresh remains. It also considers whether colonisation results in localised thermogenesis in a similar manner to that induced by blowfly larvae. In the laboratory, adult D. maculatus instantly colonised fresh killed rats and mice. The adults entered the oral cavity within 1-2 h and the eyes and ears were among the first parts of the body consumed. Egg laying occurred on the torso and head within an hour of death and eggs hatched within 3-4 days. The larvae remained on the body whilst the adults (>70%) rested in the surrounding wood chippings when not feeding or laying eggs. Larvae grew rapidly on the dead bodies and some were starting to pupate within 28 days. The dermestids consumed the corpses predominantly from the head downwards and weight loss correlated with the number of larvae produced. In both rats and mice, colonisation of the abdominal region was associated with an increase in temperature. The maximum abdominal temperature and the length of time the temperature remained 1 °C or more above ambient correlated with the number of larvae produced. This rise in temperature would probably be sufficient to increase the rate of development of dermestid larvae and that of any other invertebrate or microbe in the region. In the absence of dermestids, the internal temperature rarely rose 1 °C above ambient. Although there are previously published accounts of dermestid beetles consuming fresh corpses, they are reputed to favour older desiccated remains. This paper confirms that D. maculatus rapidly consumes and reproduces on fresh remains. The fact that dermestid beetles are seldom found on fresh remains under field conditions is therefore probably a result of inter-specific competition among decomposing insects rather than food preference. This information could be useful when determining the forensic significance of D. maculatus recovered from dead bodies.