The interaction of the rat tapeworm, Hymenolepis diminuta, with its intermediate beetle host, Tribolium confusum, is a well-studied model system. However, there is so much variation in the methods and designs of the studies that it is difficult to draw comparisons. This study simultaneously compared several aspects of the infection protocol including beetle age, sex, density and mating status; parasite egg condition, infection environment humidity and the times for the three steps of infection: starvation, feeding and post-feeding development. Although statistically limited by low prevalence and intensity levels, we were able to detect the relative effects of the variables. The effects of these variables on prevalence (percent infection) and intensity (mean number of cysticercoids) do not necessarily correlate with each other. Egg condition, reduced starvation times, higher beetle density and longer development times reduced prevalence. However, differences in intensity were only detected with older beetles. When coupled with survivorship data, our study found that our current infection protocol is optimal for infection success. However, the results suggest extending the study to other intermediate hosts and the inclusion of additional variables.

Hosts face mortality from parasitic and environmental stressors, but interactions of parasitism with other stressors are not well understood, particularly for long-lived hosts. We monitored survival of flour beetles (Tribolium confusum) in a longitudinal design incorporating cestode (Hymenolepis diminuta) infection, starvation and exposure to the pesticide diatomaceous earth (DE). We found that cestode cysticercoids exhibit increasing morphological damage and decreasing ability to excyst over time, but were never eliminated from the host. In the presence of even mild environmental stressors, host lifespan was reduced sufficiently that extensive degradation of cysticercoids was never realized. Median host lifespan was 200 days in the absence of stressors, and 3–197 days with parasitism, starvation and/or DE. Early survival of parasitized hosts was higher relative to controls in the presence of intermediate concentrations of DE, but reduced under all other conditions tested. Parasitism increased host mortality in the presence of other stressors at times when parasitism alone did not cause mortality, consistent with an interpretation of synergy. Environmental stressors modified the parasite numbers needed to reveal intensity-dependent host mortality, but only rarely masked intensity dependence. The longitudinal approach produced observations that would have been overlooked or misinterpreted if survival had only been monitored at a single time point.

We studied the ‘crowding effect’ in Tribolium confusum infected with Hymenolepis diminuta. Manipulations included age and number of parasites, and diet, sex, age and number of exposures of hosts. Volume per parasite was unaffected until an intensity of at least 5–10 parasites per host, then declined approximately inversely as intensities increased. Parasite size was affected by host sex but not age or reproductive status. Host diet affected parasite size and the impact of crowding. Daily gain in parasite volume peaked partway through the developmental period and preceded the first evidence of a crowding effect. Parasites that established during a second exposure had a transient developmental delay but eventually grew as large or larger than parasites from a single exposure with the same total intensity. Parasites responded to crowding by differential allocation of resources. Cercomer volume decreased even with slight crowding, the capsule surrounding the scolex was not reduced until crowding became more severe, and scolex width was reduced only in the most extreme conditions. The data support the hypothesis that the crowding effect in this system is driven primarily by nutrient, rather than space limitations.

Four synthetic juvenile hormone analogues (JHAs) with high morphogenetic activity on a variety of insects prevented embryonic development of Tribolium confusum to varying degrees when applied to freshly laid eggs. At 1 ppm (v/v) of the JHAs a few eggs hatched; however, some of the larvae died within a day of hatching. Older eggs were totally insensitive to JHA treatment even at higher concentrations. Larvae that hatched from these eggs appeared to be perfectly normal and continued to develop into apparently normal larvae.

Laboratory experiments were carried out to study the effect of irradiating T. confusum pupae on the susceptibility of their adults to four insecticides. Results indicate that gamma irradiation significantly decreased the tolerance of adults from pupae irradiated 1 and 2 days before eclosion to Duradin. On the contrary, malathion and formothion, belonging to the same chemical group, i.e. organophosphate, were similar in their toxicity to adults, showing that irradiation of pupae afforded some protection to adults from death. However, s. fenvalerate exhibited the same trend noticed for malathion and formothion where irradiation of pupae reduced its effectiveness to adults. In general, adults from pupae irradiated 1 and 2 days before eclosion were less tolerant to tested insecticides than those from pupae irradiated 3 days before eclosion. Studying of tolerance ratio of various insecticides revealed that at 24 hr post-treatment, the most obvious trend is that adults from irradiated pupae, 3 days before eclosion, showed a moderate level of tolerance to formothion (3.29-fold) and s. fenvalerate (3.62-fold), and high level of tolerance to malathion (16.30-fold). While all adults from irradiated pupae elucidated different levels of tolerance to malathion, formothion and s. fenvalerate, the effectiveness of Duradin on those adults was significantly enhanced. This means that the application of Duradin in combination with gamma radiation is more effective than their separate applications. The dissimilarity of adult responses to the insecticides may be attributed to the enzyme alterations, either quantitative or qualitative and are the key to these irradiation effects on toxicity of insecticides to insects.

Juvenile hormone analogues (JHAs), JHA I (6,7′-epoxy-3′,7′-dimethyl-dec-2′-enyl 6-ethyl-3-pyridyl ether), JHA II (3′,7′-dimethyl-undec-2,6′-dinyl 6-ethyl-3-pyridyl ether), MV-678 (2-methoxy-9-[4-isopropyl phenyl]-2, 6-dimethylnonane), and R-20458 (4-ethylphenyl-6, 7′-epoxy-geranyl ether) in acetone solution were applied to insect diets at 10ppm (v/v), and their effects on four species of stored products beetles observed. The larvae of the flour beetles, Tribolium confusum Jacquelin duVal, and Tribolium castaneum (Herbst), reared in media treated with JHAs I and II failed to pupate. At the end of the 6-week observation period, these larvae had not yet pupated. MV-678 and R-20458 produced ecdysial failures, lethal morphological abnormalities and larval/pupal and pupal/adult intermediates. Only a few apparently normal adult flour beetles emerged from these treatments. The lesser borer grain beetle, Rhizopertha dominica (Fabricus), completely failed to reproduce in a medium treated with JHA I. JHA II, MV-678 and R-20458 affected the reproduction of the two grain beetles, R. dominica and Sitophilus oryzae (L.), to varying extent, with MV-678 being the least potent JHA.

A laboratory study was carried out in Egypt to determine the effect of combining treatments of gamma radiation and methyl bromide fumigation applied to adults of Tribolium confusum (Duv.). An interaction between irradiation and insecticidal treatment was obvious, with additive effects noted at most combination treatments. When the irradiation treatments were applied first and fumigation were accomplished within 24 hr., the intermediate dosage of irradiation (6 krad) afforded the insects some protection against marginally effective dosages of methyl bromide after 14 days. On the contrary, it is evident that a possible synergistic effect of irradiation pretreatment followed by chemical exposure, after 21 days, where all of irradiation dosages used (2-10 krad) enhanced the fumigant effectiveness. On the other hand, when the irradiation dosages were increased from 5-50 krad and followed by fumigant treatments after 7 days, the trend did continue where all combination treatments killed more insects than did either treatment applied alone. Conversely, when fumigation preceded treatment with irradiation the sublethal methyl bromide fumigation also apparently leaves the surviving insects in a debilitated state and became more radiosensitive.

In general, the effects from combination of irradiation and fumigation were more effective than were the effects of either treatment given singly, whether irradiation preceded insecticidal treatment or vice versa.

The insect growth regulator, 6′,7′-epoxy-3′-ethyl-7′-methyl-dec-2′-enyl 6-ethyl-3-pyridyl ether, at 10 ppm applied to rearing media, did not prevent oviposition or hatchability of the eggs of Tribolium confusum. The insect growth regulator (IGR) apparently had no effects on the development of younger larvae, and no morphological abnormalities were observed in these instars. However, the IGR prevented metamorphosis of the last larval instar. These larvae continued to moult several times, became larger than larvae in untreated food, but failed to pupate; as a result, no adults emerged from the treatments.

Nutritional efficiency of four dehydrated and powdered tapioca puddings for Tribolium confusum (duVal) was assayed by studying growth, survival and fecundity of the confused flour beetle on these diets.

The common pudding inflicted about 50% mortality and caused over three-fold growth retardation in the larvae. The longevity and fecundity of the adults also were significantly reduced (P < 0.01). On the other three test puddings which contained less vitamins and more fat or carbohydrate than the common pudding, growth was even more severely retarded, and only 9% of the larvae became adults of doubtful reproductive ability. Results obtained from puddings supplemented with vitamins, or made with synthetic milk in which vitamin and fat levels were manipulated, suggest that the nutritional inadequacy of the four test puddings was mainly due to low vitamin and high fat contents.

The results demonstrate the practicality of inducing ‘self-protection’ against insect pests in certain types of food products without seriously affecting their acceptability by man.

Neyman, Park and Scott (1956) describe an experiment which they performed to determine the spatial distribution of Tribolium confusum developing within a closed container. To explain the concentration of beetles at the boundary a birth–death–migration model is developed in which the beetles may migrate over a set of lattice points, and this is shown to produce a distribution of the required shape. Not only is this distribution independent of the number of lattice points, but it is also indistinguishable from the associated diffusion process.