Thomas M. Perring

Background: Wolbachia bacteria are estimated to occur in more than half of all insect species. In Hymenoptera, Wolbachia often manipulates its host’s reproduction to its own advantage. Wolbachia is likely the reason that males are rare in the uniparental Ooencyrtus mirus Triapitsyn & Power (Hymenoptera: Encyrtidae). The likelihood of producing male offspring can be increased by giving mothers a continuous supply of Bagrada hilaris (Burmeister) (Heteroptera: Pentatomidae) host eggs to parasitize for 2–3 weeks, by feeding the parents antibiotics, or by rearing parent wasps at high temperatures; all variables that have been shown to correlate with depleting Wolbachia titers in other organisms. The purpose of the current study was to determine whether thelytoky in O. mirus is due to Wolbachia, and if so, at what time in development the sex change occurs. We also wished to determine if Wolbachia removal results in the production of intersexes, as in some other hymenopterans. Finally, mating behavior was observed to see if and where it breaks down as a result of the species becoming thelytokous. Methods: Females were collected from parental lines of O. mirus reared at 26, 30, 31, 32, 33, 34, and 36 °C. The offspring of these females were reared at 26 °C, and their sex-ratio was determined. In a subsequent experiment, the parental generation was switched between 26 °C and 36 °C during development to narrow down the critical period at which changes occurred that subsequently affected the sex-ratio of their offspring. Results: The sex ratio was male biased in the offspring of O. mirus parents reared at 34 °C and 36 °C (high temperatures), even if the offspring themselves were reared at 26 °C. The constant temperature at which the percentage of males started to increase after two generations was 31 °C (10% males), rising to 39% males at 33 °C, and 100% males at 34 °C and 36 °C. Lasting more than 2 days, the critical period for the change toward a male biased sex ratio was during the second half of the parent’s development. Molecular diagnostic assays confirmed that O. mirus females contain Wolbachia and males do not. Examination of preserved males and male-female pairs under a dissecting microscope showed no signs of intersex characters. Observation of the mating behavior of live O. mirus showed that males initiate courtship by drumming their antennae on a female’s antennae, but after a few seconds, the females typically turn and walk away. However, a few instances of possible copulation were noted. Conclusions: As hypothesized, the results indicated that thelytoky in O. mirus is likely mediated by Wolbachia bacteria. To maximize the population growth rate without generating males, the best temperature for mass rearing this species is 30 °C.

The developmental time of pink hibiscus mealybug, Maconellicoccus hirsutus (Green), immatures was investigated on the host plant Cucurbita moschata Duchesne ex Poiret variety ‘Black Futsu.’ Because host plant species influences developmental rates of M. hirsutus, understanding the life history of this specific host plant has implications for the mass rearing protocols of its natural enemy, Anagyrus callidus Triapitsyn, Andreason and Perring, currently being released in California, United States. Fruit from ‘Black Futsu’ squash were infested with first instar pink hibiscus mealybug and kept at 26.6 ± 2°C, 50 ± 10% RH, and 0:24 (L:D) h photoperiod for the duration of the experiment. Every 24 h the life stages of pink hibiscus mealybug individuals on the squash were recorded. After adult eclosion, observations of adult females continued until the first eggs hatched, which revealed an average pre-oviposition period of 7.2 ± 0.1 d and an average length of the egg stage of 7.0 ± 0.0 d. The average developmental times for both sexes were similar from the egg stage through the second instar. Third instar females took nearly twice as long (7.2 d) to develop into adults as did third instar males. However, females have just three immature instars while males have four. The males spent an average of 4.5 ± 0.3 d as third instars and 4.8 ± 0.4 d as fourth instars before developing into winged adults. On average, female immature developmental time was 27.8 ± 0.2 d from egg to adult and male developmental time was 29.4 ± 0.2 d from egg to adult. The implications of these results on rearing A. callidus are discussed.

Girault (1917) very briefly described and diagnosed the encyrtid wasp species Ooencyrtus californicus Girault (Hymenoptera: Encyrtidae) with the following limited data (p. 22): “Sacramento, California, from bug eggs on Pinus sabiniana, September”. The first author examined its two syntypes, poorly mounted on a slide, of which only parts of the four antennae and a slightly damaged fore wing remain (Triapitsyn et al. 2020). They concluded that this species was better considered a nomen dubium until fresh specimens could be collected from the same host plant in or near the type locality. In July 2019, an effort was made to re-collect O. californicus from foothill (or gray) pine, Pinus sabiniana (Pinaceae), in the Oakhurst area of Madera County, California, USA, where this pine is abundant, but no specimens were captured. At the same time, a very similar insect was collected from sentinel eggs of the invasive stink bug Bagrada hilaris (Burmeister) in Riverside, California. This insect was cultured in the laboratory as part of a B. hilaris biological control program. Due to the poor preservation of the type specimens and in the absence of genetic evidence, it was impossible to positively and properly attribute specimens of this newly collected parasitoid to O. californicus. Therefore, to provide a much needed scientific name for this native egg parasitoid, it was described as Ooencyrtus lucidus Triapitsyn & Ganjisaffar in Triapitsyn et al. (2020). The two nominal species were separated based on minor differences in the proportions of the scape, pedicel, and first funicular segment of the female antenna (Triapitsyn et al. 2020). John S. Noyes, world expert on Encyrtidae and one of the reviewers of Triapitsyn et al. (2020), disagreed with the erection of O. lucidus as a new taxon based on the morphological similarities of the female antenna with that of O. californicus, so the description was published with the understanding that the two might be conspecific. But to settle this one way or another new specimens of O. californicus had to be collected to allow morphological and molecular analyses.

The invasive stink bug, Bagrada hilaris (Burmeister) (Hemiptera: Pentatomidae), is a serious pest of cole crops. Studies are underway to assess the potential of an exotic egg parasitoid from Pakistan, Ooencyrtus mirus Triapitsyn & Power (Hymenoptera: Encyrtidae), as a biological control agent for this pest. In the present study, the ovipositional preference of O. mirus reared for multiple generations on B. hilaris, Thyanta pallidovirens (Stal), or Nezara viridula (Linnaeus) (Hemiptera: Pentatomidae) for eggs of these three stink bug species was evaluated. The first host accepted for oviposition, the number of parasitoid eggs (as indicated by pedicels) laid on each host egg at different time intervals, and the number of wasps that emerged from parasitized eggs were recorded. Results show that O. mirus prefers eggs of its primary host, B. hilaris, for oviposition over the alternate hosts tested regardless of whether the parasitoids were reared on the primary or alternate hosts. The percent parasitism in the first 2 h of exposure also was higher on B. hilaris eggs although it was not significantly different from T. pallidovirens eggs for parasitoids reared on B. hilaris and N. viridula eggs. For all parasitoid populations, the mean number of emerged wasps per host egg ranged from 0.9 to 1.1 with no significant differences. Bagrada hilaris eggs were significantly smaller than T. pallidovirens and N. viridula eggs and female wasps that emerged from B. hilaris eggs had significantly shorter body length and head width than those that emerged from T. pallidovirens and N. viridula eggs.

Bagrada hilaris (Burmeister) is a serious pest on brassica crops in many regions throughout the world. As part of our efforts to enhance biological control, we have been studying an egg parasitoid that was collected from B. hilaris eggs found on brassica plant debris in Pakistan. This species has recently been described as Ooencyrtus mirus Triapitsyn & Power. A major component of rearing biological control agents is understanding the relationship among host egg age, parasitoid age, and reproductive success. To this end, we used a factorial design to evaluate all combinations of host egg ages 0–5 d and parasitoid ages 0–11 d. The results showed that the best combinations are 0- to 1-d-old host eggs with 3- to 10-d-old parasitoids. A further study using frozen host eggs showed that O. mirus can reproduce as successfully on frozen B. hilaris eggs as on fresh ones.

Anagyrus callidus Triapitsyn, Andreason & Perring (Hymenoptera: Encyrtidae), recently described from southern California, USA and Mexico, is a primary parasitoid of the pink hibiscus mealybug, Maconellicoccus hirsutus (Green) (Hemiptera: Pseudococcidae). This wasp species previously was misidentified as Anagyrus kamali Moursi, which was introduced and released as such in the United States (California and Florida) and Mexico. In this paper, the origin of A. callidus is shown to be from Taiwan, based on differences in the morphology and molecular sequences of voucher specimens of an earlier colony of the misidentified A. kamali from Puerto Rico (released in August 2002 in southern Florida), and specimens that originated in southern Taiwan.

A new species of the encyrtid wasp genus Anagyrus Howard (Hymenoptera: Encyrtidae), Anagyrus trabutinae Triapitsyn & Andreason, is described and illustrated. Its type series was reared from the mealybug Trabutina serpentina (Green) (Hemiptera: Pseudococcidae) on tamarisk, Tamarix spp. (Tamaricaceae), on the Dead Sea shore at an elevation of 402 m below sea level. Using a combination of morphological methods and genetic analyses, the new taxon is separated from the other species comprising the Anagyrus pseudococci species complex. Its relationship to the complex is discussed. http://www.zoobank.org/urn:lsid:zoobank.org:pub:1830EE7F-C358-40CD-93E1-FFA19CA0D9DF

The pink hibiscus mealybug, Maconellicoccus hirsutus (Green) (Hemiptera: Pseudococcidae) is a pest of many plants, and a new problem on dates in California. The effects of seven insecticides and water on different life stages of this mealybug were studied to identify the best material for control. Water did not have any significant effect on mealybugs, but the insecticide treatments significantly affected all life stages tested. The egg hatch rate ranged from 28.5% to 17.2% for spirotetramat, bifenthrin, flupyradifurone, fenpropathrin, and buprofezin treatments, and was lower for sulfoxaflor (2.8%) and acetamiprid (0.1%). Despite high survival of neonate crawlers in the non-treated control and water treatments, 53.1% and 34.6% survived in the spirotetramat and buprofezin treatments, respectively; survival was zero in the other treatments. Spirotetramat and buprofezin caused very low mortality of nymphs in the first day post-treatment, but mortality significantly increased over time and reached 42.8% and 50.6% by day 6, respectively. The other treatments were highly toxic to the nymphs (79.4–99.4% on day 6). Insecticides also had a significant effect on the feeding ability of nymphs. By day 6 after treatment, 73.9% to 100% of nymphs treated with different insecticides stopped feeding although they were still alive. Insecticides showed no effect on the mortality of adult females, but the percentages of ovipositing females were significantly reduced (51.1% to 10.6%) in all insecticide treatments, except buprofezin, which was not statistically different from water and the non-treated control. In the process of our studies, we identified abnormalities in the appearance of eggs from females treated with various insecticides, and these aberrant eggs are described.