Infection With The Pinworm Blatticola Blattae And Survival of Starving German Cockroaches, Blattella Germanica

The German cockroach, Blattella germanica, is often infected with the pinworm, Blatticola blattae. To investigate the effect of pinworm infection on cockroach survival, we articially manipulated the pinworm infection status of two lines of German cockroaches kept in the laboratory and compared survival rates in starvation. Of the two lines of German cockroaches WATn and NIIDp bred in the laboratory, the WATn line was not infected with pinworm, and the NIIDp line was naturally infected with pinworm B. blattae. The WATp line was created by articially infecting the pinworm B. blattae with this WATn line. The NIIDn line was created by treating the NIIDp line with anthelmintic drugs. The 50% survival days of uninfected WATn line of starving cockroaches was 8 days, and infected WATp line of starving cockroaches was 13 days. The 50% survival days of naturally infected NIIDp line of starving cockroaches was 6 days, and that of anthelmintic-treated NIIDn line of cockroaches was 4 days. The survival days were signicantly longer in pinworm-infected cockroaches than uninfected or anthelmintic-treated cockroaches. These results suggest that pinworm infection enhances the survival of cockroaches under starving conditions.


Introduction
The German cockroach, Blattella germanica, is frequently infected with the pinworm, Blatticola blattae (Kobayashi et al. 2021).Although pinworm infection is common among cockroaches worldwide, few reports have described the effects of parasite infection on the insect host.In order to investigate the effects of nematode infection in cockroaches, it is necessary to control the pinworm infection.Kobayashi et al. (2021) reported that German cockroaches can be easily infected with B. blattae via contact with feces from pinworm-infected cockroaches.Anthelmintics of pyrantel pamoate and pyrvinium pamoate were reported to be effective for deworming B. blattae in the German cockroaches, without causing mortality for the host (Kobayashi et al. 2020).Based on these reports, we established a line of German cockroaches that originated from a pinworm-free line and arti cially infected the cockroaches with pinworms.We also established an anthelmintic-treated line of German cockroaches that originated from a line naturally infected with pinworms.
The purpose of this study was to investigate the effect of B. blattae infection on the survival of German cockroaches under starvation conditions.We compared the number of days until the cockroach survival rate reached 50% for cockroaches that arti cially changed the pinworm infection status.

German cockroach
Four lines of German cockroach (WATn, WATp, NIIDn, and NIIDp) were used in the study.WATn is originally a pinworm-uninfected WATARIDA strain, and is abbreviated as WATn by adding "n" which means pinworm-negative.WATp is a cockroach strain that arti cially infected the WATARIDA strain with B. blattae, and is designated as WATp by adding "p", which means pinworm-positive.WATn cockroaches were arti cially infected with B. blattae by exposing them to feces of infected cockroaches for 6 months in the breeding environment.The prevalence of B. blattae infection was 0% (0/40) in the WATn line and 83% (20/24) in the WATp line.
NIIDp is naturally pinworm-infected NIID strain, with "p" meaning pinworm-positive.The NIIDn strain was arti cially generated by treating pinworm-infected NIIDp line with an anthelmintic (2000 ppm pyruvinium pamoate solution) for 16 days, and the negative meaning "n" was added to make NIIDn.The prevalence of B. blattae was 93% (40/43) for the NIIDp line and 6.7% (1/15) for the NIIDn line.
Adult German cockroaches 3 to 30 days old for the WATp and WATn lines and 24 to 50 days old for the NIIDp and NIIDn lines were used in the study.

Cockroach breeding environment
A total of 10 to 15 adult German cockroaches were bred in a plastic cage (size: 175 × 140 × 105 mm) with a porous cover to allow air entry.Escape of cockroaches was prevented by applying a 50-mm wide layer of Vaseline (manufactured by Kanto Chemical Co., Inc.) to the upper surface of the inner wall of the container.A piece of folded paper (approx.70 × 70 mm in size) was placed in the cage to provide a hiding place.Water and food (control area only) were also provided, and the cages were kept in a constant temperature environment (25 ± 1°C).

Comparison of survival rate
Pinworm-infected cockroaches (WATp & NIIDp), uninfected cockroaches (WATn), and anthelmintic-treated cockroaches (NIIDn) were bred separately in two groups, a normal feeding group and a non-feeding group.The number of surviving cockroaches was recorded at the end of each day.Feces excreted by the cockroaches during the test period were not removed until the end of the experiment.

Statistical analysis
each group, the 50% survival days (the number of days until the survival rate reached 50%) was determined from the survival rate in the elapsed days.The 50% survival days was calculated according to the Kaplan-Meier method and the log-rank test was used to examine the signi cance of the differences.
The analysis was performed in a high-level test using Statcel4 software (OMS Publishing, Tokyo, Japan) and a P value of ≤0.05 was considered signi cant.

Results
Table 1 summarizes the results of a comparison of the number of surviving cockroaches between the pinworm-infected lines (WATp and NIIDp) and uninfected line (WATn) or anthelmintic-treated line (NIIDn).
WAT line was used in Experiment 1 and NIID line was used in Experiment 2. When fed a normal diet, 100% of the cockroaches in both experiments survived to the end of the study period.In the absence of food, survival of WATn cockroaches reached 50% after 8 days, whereas 13 days were required for survival of WATp cockroaches to reach 50%.In Exp. 2, survival of anthelmintic-treated NIIDn cockroaches declined to zero in 6 days, but NIIDp cockroaches continued to survive even after 10 days.2) The prevalence of B. blattae in the WATp and WATn lines was 83% (20/24) and 0% (0/40), respectively.WATp cockroaches were experimentally infected with pinworms via exposure to feces from pinworm-infected cockroaches in the breeding environment.The prevalence of B. blattae in the NIIDp and NIIDn lines was 93% (40/43) and 6.7% (1/15), respectively.The NIIDn group is a line in which the infection rate was reduced by treatment of pinworm-infected NIIDp roaches with an anthelmintic agent (pyrvinium pamoate 2000 ppm solution) for 16 days.

Figures Figure 1
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Table 1 .
Comparison of the number of surviving German cockroaches, Blattella germanica, between pinworm (Blatticola blattae)-infected lines and un-infected or anthelmintic-treated lines.