Instar Bugs Research Articles

Potential of Blaptostethus pallescens Poppius (Hemiptera: Anthocoridae) on Tetranychus truncatus Ehara (Prostigmata: Tetranychidae)


 Efficiency, functional and numerical responses of anthocorid bug Blaptostethus pallescens Poppius on the spider mite, Tetranychus truncatus Ehara were examined under laboratory conditions. Nymphs of B. pallescens exhibited a Hollings type II functional response when females of spider mite were offered at densities of 10, 20, 30, 40, 50, 60 and 70 mites/bug. Individual fifth instar bugs consumed up to 45.3 adult females of T. truncatus in 24 h at prey mite densities of 60 mites/ bug. Studies on numerical response revealed that the nymphs of the anthocorid bug failed to complete development when the food was restricted to mite alone. Numerical response studies on adult bugs, when offered T. truncatus at densities of 10, 20, 30, 40 and 50 females showed no significant differences in the average fecundity of the female bug. Results indicate that the anthocorid predator, B. pallescens has a very high predatory potential though with a weak numerical response.

Keeping cool: Kissing bugs avoid cannibalism by thermoregulating

Kissing bugs possess a highly developed thermal sense and when starved, they attempt to bite any object which temperature is close to that of a warm-blooded host. At each feeding event, these insects take massive meals in just a few minutes. One could then expect fed-bugs being heated-up by the ingested warm blood and so becoming attractive to starved conspecifics. This is not however the case, arising the question about why cannibalism is very rare among these insects. Recently, the ability of thermoregulating during feeding has been demonstrated in Rhodnius prolixus. These bugs possess a countercurrent heat-exchanger that cools down the ingested blood, before it reaches the abdomen. We hypothesise that avoiding thermal stress is not the only adaptive advantages of this mechanism, but could also help avoiding cannibalism. We tested this hypothesis by quantifying cannibalism by never-fed first-instar larvae on: (1) just-fed 5th instar bugs, (2) artificially heated just-fed bugs, (3) heated or (4) non-heated objects of the same size. In line with our hypothesis, non-heated just-fed bugs were not attacked by the 1st instar larvae, whereas heated bugs and object triggered biting behaviour in starved bugs, which performed either cleptohaematophagy or haemolymphagy on heated bugs. We conclude that cannibalism triggered by thermal stimuli has been one of the selection pressures that gave origin to thermoregulation during feeding on kissing bugs.

Seasonal dynamics in the numbers of parasitic bugs (Heteroptera, Cimicidae): a possible cause of roost switching in bats (Chiroptera, Vespertilionidae)

The objective of the present paper is to extend the knowledge of roosting strategies of bats and the interaction of bats with their roost ectoparasites, the bat bugs Cimex pipistrelli. The project was focussed on the potential causality of bat movements and the variation in bug numbers. For 2 years, three model bat boxes with breeding female Pipistrellus pygmaeus were monitored inside floodplain forest. After the arrival of bats in May, adults and first instars of bugs were observed in the boxes. During the lactation period in June, when the bats did not occupy the roosts, the first instar bugs died out followed by the adults. The decrease in bug numbers began only several days after the bats had left the boxes. After a month of the bats' absence, the abundance of adult bugs decreased by half of their number. Only the eggs survived the period when the roosts were unoccupied in summer. In mid-July, after the arrival of lactating females, an increase in the number of bugs was observed. At the beginning of August, however, no new eggs were found. Although adult C. pipistrelli are able to survive the winter period in the boxes, the bats, by shifting the roosts within the vegetation season, prevent the massive reproduction of these parasites.

No change in one biological parameter for Dipetalogaster maximus after 20 years of laboratory colonisation.

The value of Dipetalogaster maximus as a xenodiagnostic agent has been reviewed2. We have always worried that the due to inbreeding in our laboratory colony our off-spring would suck less blood. An opportunity to test this risk arrived with 60 eggs retrieved from a wild caught female of the Baja California Peninsula. Instars from these eggs were weighed before and after each meal. A control group of same instar bugs from the Brasilia colony which has been in existence twenty years was investigated at the same time. All bugs were maintained at 26°C and 70% humidity and fed on chicken blood. They were weighed individually on a balance sensitive to 0.5 milligram. Thirty individuals of each juvenile instar were used and ten of .both sex adults for the two colonies 1973 and 1993. The results are shown in the Tables. The statistical analysis is that of Levine1 for comparing samples of different size. Table 1 shows the summarised data of blood meal weight in the two colonies 1973 and 1993. Table 2 records the T values (actual and expected) and the degree of freedom related to this data. Only two instars were significantly different in the two colonies. The second instar fed significantly more in the 1993 group and adult females the reverse (a stage of more relevance to our colony needs). Possibly if the groups had been larger these differences would also disappear. The data suggest that after twenty years in colony blood ingestion of the different instars of D. maximus has not changed.

Resistance of unfed first instar Dipetalogaster maximus to different environmental conditions.

We have already determined the favourable temperature and humidity conditions for rearing D ipeta logaster maximus1. In each of the two experiments described here two newly hatched lots of 40 first instar bugs were studied. One group was maintained in our insectary at a mean temperature o f280 C (range 27-30) and a mean humidity of 50 % (range 47-50 %). The second group was maintained in the laboratory during the period October to March when conditions were colder (22°C, range 1034) and drier (40 % range 10-90). Time to death of these unfed bugs was recorded for all experimental insects. The results are expressed in Figure 1. They show that first instar bugs kept in drier, colder conditions live significantly longer (mean 145 days, range 94-178) than those kept under our insectary conditions (mean 89 days, range69-103) (x2=0.582, p = 0.4555). While our insectary is favourable for rapid rearing of fed bugs1, it shortens the life of unfed first instars. These data are compatible with field observations2. First instars survived in the cold nocturnal conditions of the Baja California Peninsula to run over sunlit stony ground from 9 a.m. in search of the rare blood meal. Their resistance to starvation is a biological adaptation to an inhospitable ecology.

The isolation of acid phosphatase isoenzymes of Oncopeltus fasciatus, (Dallas) (Hemiptera: Lygaeidae)

1. 1. Acid phosphatase isoenzymes of selected ages of fourth, fifth, and adult stage milkweed bugs were isolated by CM-cellulose and DEAE-cellulose chromatography and gel electrophoresis. 2. 2. Acid phosphatase-I (AP-I) and acid phosphatase-II (AP-II) were isolated by CM-cellulose chromatography and were found in all examined bugs. 3. 3. Day 14 adult females gave a third isoenzyme, AP-III, from the CM-cellulose column. When acid phosphatase-III (AP-III) was applied to the DEAE-cellulose column, three additional isoenzymes, acid phosphatase-III-1 (AP-III-1), acid phosphatase-III-2 (AP-III-2), and acid phosphatase-III-3 (AP-III-3), were isolated. 4. 4. Gel electrophoresis separated acid phosphatase-I (AP-I) into two isoenzymes, AP-I-1 and AP-I-2, in samples from all groups except the Day 14 adult male which had only AP-I-1 on gels run at pH 8.3. 5. 5. Acid phosphatase-II (AP-II) was a single diffuse band in all groups on gels run at pH 4.5. 6. 6. Acid phosphatase-III-1 (AP-III-1), acid phosphatase-III-2 (AP-III-2), and acid phosphatase-III-3 (AP-III-3) from Day 14 adult females gave each a single diffuse band on gels run at pH 4.5. 7. 7. Juvenile hormone application to the fifth instar bugs had no effect on acid phosphatase activity, total protein, or the electrophoretic separation of acid phosphatase isoenzymes of the fifth instar bugs when compared to the acetone controls.

Studies on Trypanosoma rangeli Tejera, 1920. IX. Course of infection in different stages of Rhodnius prolixus.

Frequent individual observations od different stages of Rhodnius prolixus exposed to Trypanosoma rangeli, revealed a higher susceptibility to infection in the bugs exposed during the two first instars. The mortality rate in infected bugs was significantly higher than in controls, indicating that the parasite was responsible for the majority of deaths. An analysis of the mortality distribution, per instar, is presented. Statistical analysis of deaths among the different infected instars, showed that T. rangeli produces its pathological effect in any stage of R. prolixus independently of its susceptibility to the parasite. The survival to adult decreased in all the infected instar bugs. A significant longer time to reach the adult stage was observed in the infected bugs when compared with controls, excepting for specimens exposed in the third instar. The epidemiological significance of the present results is discussed.

An outbreak of acute Chagas's disease in the São Francisco Valley region of Bahia, Brazil: triatomine vectors and animal reservoirs of Trypanosoma cruzi

Following reports of an unusually high incidence of acute Chagas's disease and the appearance of large numbers of Triatoma infestans in the southwestern region of the State of Bahia, triatomine bugs (Hemiptera: Reduviidae) and domestic animals in one of the affected communities were surveyed and examined for infection with Trypanosoma cruzi. Triatoma infestans was prevalent in houses and was also found in peridomestic habitats. T. sordida and T. pseudomaculata occupied peridomestic and sylvatic habitats and T. brasiliensis was found only among rocks far from houses. Panstrongylus megistus, formerly present in the region, was not found. Trypanosoma cruzi was detected in 19·5% of Triatoma infestans, 11·5% of T. sordida, 19% of dogs, 29% of cats and 100% of rats examined. A disproportionate number of early instar bugs were infected with Trypanosoma cruzi, suggesting that a rapid increase in the rate of transmission had recently occurred. The history of the domestic triatomine fauna of the region since 1912 is reviewed, and it is proposed that the relatively recent arrival of Triatoma infestans initiated a domestic cycle linked to peridomestic and sylvatic cycles of Trypanosoma cruzi transmission. Increased human mobility, the use of DDT for malaria control, and drought conditions are considered as factors which might have contributed to the outbreak of human infection.

The cuticle as a template for growth in Rhodnius prolixus

The variation in size that occurs in Rhodnius has been examined and it is found that while the size of the head in any instar is almost constant, the dimensions of the abdomen vary as weight 3 . The meal that is taken is 5·7 times the unfed weight, suggesting that the abdomen stretches by a standard ratio regardless of size. In the adult the size of the abdomen is neither constant nor varies as weight 3 and the size is difficult to predict from the size of the fifth instar larva. Experiments with dilute meals and constraints on the size of the cuticle showed that the size of the larval abdomen is affected by the size of the cuticle in the previous instar; the effect of nutrition on the size of the head, however, is far less great. Experiments with fifth instar bugs showed that the size of the abdomen of the adult was directly related to the size of the larval abdomen at about the time of the deposition of the epicuticle. A model has been suggested to describe the growth of Rhodnius which proposes that the size in the next instar is the product of the existing size and a local growth factor. The local growth factor may change at metamorphosis and is probably expressed at the cellular level in terms of cell density and the area of epicuticle deposited per cell.