Inequalities in body size among mermithid nematodes parasitizing earwigs.

Variation among body sizes of adult parasitic worms determines the relative genetic contribution of individuals to the next generation as it affects the effective parasite population size. Here, we investigate inequalities in body size and how they are affected by intensity of infection in Mermis nigrescens (Mermithidae: Nematoda) parasitizing the European earwig Forficula auricularia in New Zealand. Among a population of pre-adult worms prior to their emergence from the host, we observed only modest inequalities in body length; however, among worms sharing the same individual host, inequalities in body sizes decreased with increasing intensity of infection. Thus, the more worms occurred in a host, the more the second-longest, third-longest and even fourth-longest worms approached the longest worm in body length. This pattern, also known from another mermithid species, suggests that worms sharing the same host may have infected it roughly simultaneously, when the host encountered a clump of eggs in the environment. Thus, the life history and mode of infection of the parasite may explain the modest inequalities in the sizes achieved by pre-adult worms, which are lower than those reported for endoparasitic helminths of vertebrates.

Efficacy of a mermithid nematode Romanomermis iyengari (Welch) (Nematoda: Mermithidae) in controlling tree hole-breeding mosquito Aedes albopictus (Skuse) (Diptera: Culicidae) in a rubber plantation area of Kerala, India.

In rubber plantations, tree holes are one of the major types of breeding habitats of Aedes mosquitoes which transmit dengue and chikungunya. A mermithid nematode, Romanomermis iyengari, was evaluated in tree holes for its efficacy in controlling Aedes albopictus. Infection of mosquito larvae by the nematode was determined through microscopic examination on the next day of application, and evaluation of immature density of mosquito was done on the seventh day. After application of the infective stage of the nematode in a host-parasite ratio of 1:3 or 1:4, the infection rates on the different larval instars of mosquito were similar, 85.7-95.8 % in first to third instars and 79.3 % in fourth instar larvae or 100 and 92.9 %, respectively. Parasite burden varied from 1.1 to 2.4, respectively, among first and third instar larvae applied at 1:3. At 1:4, the parasite burden was between 1.6 (fourth instar) and 4 (second instar). The increase in parasite burden due to parasite density was significant in all the larval instars (P < 0.05). High parasite burden is detrimental to parasite recycling as it can cause premature mortality of the host. Hence, the dosage of 1:3 could be considered as suitable for rubber tree hole habitats. In the nematode-applied tree holes, there was a significant level (P < 0.05) of reduction in the immature density of A. albopictus, especially late instars and pupae, confirming the efficacy of R. iyengari in infecting the mosquito and controlling pupal emergence.

Effects of insect growth regulators on the mosquito-parasitic nematode Romanomermis iyengari.

Pyriproxyfen, a juvenile hormone analogue, diflubenzuron, a chitin synthesis inhibitor, and azadirachtin, an ecdysone agonist, are three insect growth regulators (IGRs) considered as selective and effective insecticides for mosquitoes. Romanomermis iyengari (Welch) is a mosquito-parasitic mermithid that can provide biological control against many medically important mosquito species. The compatibility of these two control tactics was tested by evaluating the sublethal effects of exposure to IGR on nematode developmental stages (preparasitic, parasitic, and preparasitic + parasitic) using Culex pipiens larvae as the host. Sublethal concentrations of IGRs were 90 % emergence inhibition of host mosquito. Preparasitic exposure to pyriproxyfen, azadirachtin, and diflurbenzuron had no effect on infectivity, parasite load, sex ratio, or male size but reduced nematode female length and increased male sex ratio at one parasite/larva. When IGRs treatments were made against the parasitic and preparasitic + parasitic stages, pyriproxyfen and azadirachtin reduced R. iyengari infectivity, parasite load, and male nematode length, whereas pyriproxyfen exposure increased male sex ratio and reduced the female R. iyengari length. Thus, IGRs have significant negative impacts on different stages of mosquito mermithid that can destabilize the balance of host-parasite population interaction. Therefore, IGRs should be used with caution in mosquito habitats where these parasites have established.

Mermithid nematode infection in a colony of blue-winged grasshoppers (Tropidacris collaris).

A die-off occurred in a captive colony of blue-winged grasshoppers (Tropidacris collaris) at the Toronto Zoo. One fourth of the colony died within a year due to infection with worms initially mistaken for nematomorphs but later identified as nematodes belonging to the Mermithidae, genus Mermis. Mortality persisted and the grasshopper population dwindled over the following years. Mermithid larvae developed in the hemocoel of the insects until they eventually emerged from a hollowed-out exoskeleton. Circumstantial evidence suggests that the parasites were introduced with raspberry browse that was grown on site and contaminated with mermithid eggs.

Unique two-photoreceptor scanning eye of the nematode Mermis nigrescens.

A single eye is present in females of the nematode Mermis nigrescens. A pigment cup occupies the entire cross section near the anterior tip of the worm, and the curved cuticle at the tip becomes a cornea. The shading pigment is hemoglobin instead of melanin. The eye has been shown to provide a positive phototaxis utilizing a scanning mechanism; however, the eye's structure has not been sufficiently described. Here, we provide a reconstruction of the eye on the basis of light and electron microscopy of serial sections. Hemoglobin crystals are densely packed in the cytoplasm of expanded hypodermal cells, forming the cylindrical shadowing structure. The two putative photoreceptors are found laterally within the transparent conical center of this structure where they would be exposed to light from different anterior fields of view. Each consists of a multilamellar sensory process formed by one of the dendrites in each of the two amphidial sensory nerve bundles that pass through the center. Multilamellar processes are also found in the same location in immature adult females and fourth stage juvenile females, which lack the shadowing pigment and exhibit a weak negative phototaxis. The unique structure of the pigment cup eye is discussed in terms of optical function, phototaxis mechanism, eye nomenclature, and evolution.

Parasitoid-induced behavioral alterations of Aedes aegypti mosquito larvae infected with mermithid nematodes (Nematoda: Mermithidae).

A wide range of parasites are known to cause behavioral changes in their hosts and parasitized insects are especially amenable to the study of such changes. The majority of studies addressing parasite-induced behavioral alterations have focused on parasites with complex life cycles and the adaptive nature of such changes. Behavioral changes caused by parasitoids, single-host parasites that kill their host upon emergence, have been studied less and the adaptive nature of these changes is likely to be different than those in complex life cycles. I investigated behavioral alterations in Aedes aegypti mosquito larvae infected with parasitoid nematodes (family Mermithidae). I conducted several experiments in which I tested the following hypotheses: 1) Mermithid nematodes induce behavioral changes in mosquito larvae and the changes are density dependent. 2) Different species of mermithid nematodes induce similar changes in mosquito larvae behavior. 3) Behavioral alterations vary with mermithid developmental stage. 4) Mosquito larvae infected with mermithid nematodes behave similarly to uninfected food-deprived mosquito larvae. I found that 4th instar Ae. aegypti infected with Romanomermis culicivorax or Strelkovimermis spiculatus exhibited resting behaviors significantly more often than uninfected controls but that intensity of infection did not affect activity levels. In earlier instars, infected mosquito larvae were more active than uninfected control larvae in some behaviors associated with feeding. There was no significant difference between infected and uninfected food-deprived mosquitoes in nine of the ten behaviors observed. The decrease in activity of late instar Ae. aegypti larvae infected with mermithids may be a parasitoid adaptation that reduces the risk of predation and thus increases host and parasitoid survival. The increase in feeding activity in earlier instars as well as the similarity between uninfected food-deprived and infected Ae. aegypti behavior may indicate that these behaviors are adaptive for the parasitoid, increasing nutritional acquisition for successful parasitoid development.

Improved rearing methods for Heleidomermis magnapapula (Nematoda: Mermithidae), a larval parasite of Culicoides variipennis sonorensis (Diptera: Ceratopogonidae).

Improvements in rearing techniques have decreased maintenance needs and have increased the parasitism rate of larval Culicoides variipennis sonorensis Wirth & Jones by the mermithid nematode, Heleidomermis magnapapula Poinar & Mullens. In colony pans with 2,500-3,000 larval C. v. sonorensis, H. magnapapula adults emerged from 22.5% of hosts, with an average yield of 159 female H. magnapapula per pan. H. magnapapula females refrigerated for 1 wk showed no decline in preparasite infectivity compared with nonrefrigerated females. Female insemination did not differ with various mating combinations of 1 or 2 females with 1 or 2 males; 37-47% of these pairs failed to produce fertilized eggs. In 9-cm petri dishes, the optimal preparasite/host ratio was 900 infective preparasites (1 female's entire clutch) to 650-700 C. v. sonorensis larvae. Overall, parasite production was more time- and labor-efficient when larvae were parasitized in regular colony pans compared with petri dishes.

Experimental transmission of the nematode Echinomermella matsi to the sea urchin Strongylocentrotus droebachiensis in the laboratory.

Three experiments were conducted to investigate the possibility of maintaining the Echinomermella matsi-Strongylocentrotus droebachiensis system in the laboratory. The experiments were performed by injecting E. matsi larvae taken directly from gravid female nematodes into the mouths of sea urchins. In all experiments, this treatment resulted in a higher infection in treated animals than in unmanipulated controls. The successful establishment of larvae indicates that E. matsi has a monoxenous life cycle. The growth of larvae in experimentally infected hosts was slow, indicating that the generation time of the parasite is of the same magnitude as the life expectancy of the host, 1-2 yr. This slow growth rate suggests that considerable resources will be needed to maintain the system in the laboratory.

[Certain tasks in the studies of Mermithoidea for biological control of moths]. / Nekotorye zadachi issledovaniia mermitid dlia tselei biologicheskoi bor'by s moshkami

The method of "flooding" with mermitids, which was successfully used against mosquitoes, is unreal for biological control of black flies because of difficulties and unprofitableness of their laboratory maintenance and reproduction. A more probable way of solving the problem is the untroduction of effective forms of parasites. In perspective the cultivation of the adipose tissue of the host and biochemical overcoming of its protective reactions are necessary.

[The mass rearing of the mermithid nematode Romanomermis culicivorax]. / Massovoe razvedenie nematod-mermitid Romanomermis culicivorax.

The procedure of mass laboratory rearing of mermithid nematode Romanomermis culicivorax, a parasite of mosquito larvae, is described. Culex pipiens molestus larvae are used as a host for cultivation at the host: preparasites ratios of 1:4-1:6, enabling to obtain the greatest mass of nematodes (over 500 mg per 1 thousand of infested mosquito larvae) when the male female ratio in culture was 1:1. This rearing technique allows to obtain on average 350 thousand invasive mermithid preparasites per 1 g of adult mermithids. The above-proposed method is compared to the procedure rearing described earlier by Petersen, Willis (1972).

[Mass breeding of Romanomermis culicivorax (Nematoda: Mermithidae) in the tropical conditions of Cuba]. / Cría masiva de Romanomermis culicivorax (Nematoda: Mermithidae) en las condiciones tropicales de Cuba.

To develop the process of mass production on a large scale of the parasite nematode Romanomermis culicivorax Ross and Smith, 1976, under the control tropical conditions of Cuba, it was taken into consideration the standardization of a certain number of variables, such as: utilization of eggs in the process of infectation, dosage, types of water, types of substrate, temperature, culture methods, and storage methods of culture batches. High performances in nematoda and approximately the same amount of females and males were obtained when mosquito larvae of the species Culex quinquefasciatus Say, 1823, were exposed to parasite's infective larvae.

Effect of temperature on different stages of Romanomermis iyengari, a mermithid nematode parasite of mosquitoes.

The effect of temperature (20 degrees-35 degrees C) on different stages of Romanomermis iyengari was studied. In embryonic development, the single-cell stage eggs developed into mature eggs in 4.5-6.5 days at 25-35 degrees C but, required 9.5 days at 20 degrees C. Complete hatching occurred in 7 and 9 days after egg-laying at 35 and 30 degrees C, respectively. At 25 and 20 degrees C, 85-96% of the eggs did not hatch even by 30th day. Loss of infectivity and death of the preparasites occurred faster at higher temperatures. The 50% survival durations of preparasites at 20 and 35 degrees C were 105.8 and 10.6 hr respectively. They retained 50% infectivity up to 69.7 and 30.3 hr. The duration of the parasitic phase increased as temperature decreased. Low temperature favoured production of a higher proportion of females which were also larger in size. The maximum time taken for the juveniles to become adults was 14 days at 20 degrees C and the minimum was 9 days at 35 degrees C. Oviposition began earlier at higher temperature than at lower temperature. However, its fecundic period was shorter at 20 degrees C than at 35 degrees C indicating enhanced rate of oviposition at 20 degrees C. Fecundity was adversely affected at 20 degrees C and 35 degrees C. It is shown that the temperature range of 25 degrees-30 degrees C favours optimum development of R. iyengari.

[Fecundity and embryonal development of Romanomermis culicivorax]. / Fecundidad y desarrollo embrionario de Romanomermis culicivorax.

Romanomermis culicivorax (Ross and Smith, 1976) eggs completed the late preparasite curling phase of their embryo development in an average time of 11 days and at a temperature of 25 +/- 2 degrees C. It was also observed that female R culicivorax specimens laid 312 eggs in 13 days, when male and female specimens were placed in a substrate of distilled water with a pH = 4.5.