Pest management of postharvest potatoes: lethal, sublethal and transgenerational effects of the ectoparasitic mite Pyemotes zhonghuajia on the potato worm Phthorimaea operculella

BACKGROUND

Potato, Solanum tuberosum, is one of the most important food crops in the world, playing a significant role in global food security. However, many potato industries and farms may suffer losses of tuber yield and quality in storage due to lepidopteran pests. Here, we evaluated the effectiveness of an ectoparasitic idiobiont mite Pyemotes zhonghuajia in the biological control of the potato tuber moth (PTM) Phthorimaea operculella by determining the lethal, sublethal (nonconsumptive) and transgenerational effects of P. zhonghuajia of various population densities and exposure durations on PTM survival, development and reproduction.

RESULTS

Pyemotes zhonghuajia females were capable of killing all instar stages of PTM, while resistance to mite parasitism increased with the development of PTM life stage. The mortality of mature larvae (i.e., fourth instar) and pupae increased with increasing mite density and exposure duration. P. zhonghuajia imposed significant negative sublethal impacts on PTM pupation rate, female fecundity and adult longevity but not on immature development. The sublethal stress was transgenerational, resulting in lower reproduction in the offspring generation.

CONCLUSION

P. zhonghuajia induces lethal, sublethal and transgenerational effects and significantly decreases PTM survival and reproductive out, demonstrating its high efficiency in the biological control of PTM. Our study provides insight into the mechanisms underlying the nonconsumptive effects of parasitism in an ectoparasite-host system and delivers critical information for the design and implementation of augmentative releases of P. zhonghuajia in the biological control of PTM in potato storage. © 2023 Society of Chemical Industry.

Parasitism of Locally Recruited Egg Parasitoids of the Fall Armyworm in Africa

The fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), is an insect native to the tropical and subtropical Americas that has recently spread to Africa, where it predominately attacks maize, sorghum and other plant species. Biological control is an environmentally friendly way of combatting the pest and contributes to an integrated pest management approach. In Africa, several trichogrammatid parasitoids and Telenomus remus Nixon (Hymenoptera: Platygastridae) have been found parasitizing eggs of the FAW. In Niger, the egg parasitoids encountered include Trichogrammatoidea sp. (Hymenoptera: Trichogrammatidae) and Telenomus remus Nixon. Parasitism of the FAW eggs by the two egg parasitoids was assessed in the laboratory, followed by field testing on sentinel eggs. In the laboratory, T. remus parasitized on average 78% of FAW eggs, compared to 25% for Trichogrammatoidea sp. Telenomus remus was able to parasitize egg masses that were fully covered with scales, while Trichogrammatoidea sp. parasitized only uncovered egg masses. On-farm releases of T. remus in sorghum fields caused up to 64% of FAW egg parasitism. Parasitized eggs yielded viable progeny, which can contribute to FAW egg parasitism build-up during the cropping season. Our findings lay the groundwork for the use of T. remus in augmentative releases against FAW in Africa.

Insight into the success of whitefly biological control using parasitoids: evidence from the Eretmocerus warrae-Trialeurodes vaporariorum system

BACKGROUND

Mechanisms behind the success and failure of whitefly biological control using parasitoids are largely unknown. Here we use the Eretmocerus warrae-greenhouse whitefly system to investigate how the fluctuating density of the parasitoid and its host affects three key parasitoid fitness parameters, host searching, host feeding and parasitization, providing critical knowledge for evaluation and development of whitefly biological control programmes. This is the first such study in a parasitoid-whitefly system.

RESULTS

Models used and developed here show that (1) both host feeding and parasitism fit a type II functional response; (2) overall parasitoid-caused whitefly mortality significantly increases with growing density of both organisms and the parasitoid density has a significantly more positive effect; (3) with a pro-synovigenic nature, E. warrae allocate significantly more resources to parasitization than to host feeding activity in low whitefly density and high parasitoid density; and (4) low mutual interference among searching parasitoids encourages parasitoid aggregation on host patches of high density.

CONCLUSION

Regardless of greenhouse whitefly density, the pest can be effectively controlled by release of E. warrae. Our study provides insight into the success of whitefly biological control programmes using the parasitoid augmentation approach. Models used and developed here can also be employed to evaluate biological control programmes for other parasitoid-whitefly systems. © 2017 Society of Chemical Industry.

Effective Biological Control Depends on Life History Strategies of Both Parasitoid and Its Host: Evidence from Aphidius colemani-Myzus persicae System

Mechanisms behind the success and failure of aphid biological control using parasitoids are largely unknown, probably because of the lack of knowledge of life history strategies of the insects involved. Here, we measured and compared life history strategies of Myzus persicae (Sulzer) (Hemiptera: Aphididae) and its parasitoid Aphidius colemani (Viereck) (Hymenoptera: Aphidiidae), providing essential information for evaluation of the potential of A. colemani to control M. persicae. Our results show that one A. colemani female parasitized ≈220 aphids within 1 wk regardless of the aphid age. Almost all aphids parasitized at <4th instar died before reaching adulthood, and those parasitized at ≥4th instar produced very few offspring, contributing little to population growth. Although having 21% lower intrinsic rate of increase and 33% longer life cycle than the aphid, the parasitoid possessed reproductive output and net population growth rate twice as high as the aphid, and reached maximum lifetime reproductive potential 1 wk earlier than the aphid. The life history strategies reported here imply that A. colemani is potentially a good biological control agent of M. persicae. On the basis of this study, we hypothesize that immediately after the onset of M. persicae, a release rate of ≈1:220 (female parasitoid:aphids) at a weekly interval during the first 3 wk could effectively control the pest. We suggest that the success of biological control of aphids using parasitoids largely depends on life history strategies of both insects involved and time of the season when they meet.

Comparative studies of the influence of relative humidity and temperature on the longevity and fecundity of the parasitoid, Cotesia flavipes

The parasitoid, Cotesia flavipes (Cameron) (Hymenoptera: Braconidae), was introduced for biological control of the stemborer, Chilo partellus (Swinhoe) (Lepidoptera: Crambidae), in eastern and southern African countries. The parasitoid became firmly established in Ethiopia, with varying density and distribution in various regions of the country indicating that there are factors regulating the success of the parasitoid. From previous studies, it was known that the population of the parasitoid released, the type of host, and temperature highly affect some of the biological parameters of the parasitoid. The current studies were undertaken to understand the individual and interactive effect of temperature and relative humidity on the longevity and fecundity of C. flavipes. The study was conducted on C. flavipes collected from the Melkassa Agricultural Research Center Experimental Field, Ethiopia. C. flavipes was reared in the laboratory on C. partellus feeding on pieces of sorghum stem. The longevity experiment was conducted at 10, 20, 30 and 40 degrees C, while the fecundity experiment was conducted at 20, 25, 28 and 30 degrees C. For both experiments 40-50%, 60-70% and 80-90% relative humidity regimes were used. The results obtained indicate that the interactive effect of temperature and relative humidity significantly affected the longevity, the number of oocytes, and fecundity of C. flavipes implying that the two factors play an important role in the success of the parasitoid as a biocontrol agent against C. partellus. The results obtained suggests the importance of the selection of target release sites for maximum efficiency of the parasitoid, which can have a positive impact on the on-going augmentative release of C. flavipes in Ethiopia.