Diversity of Predators Associated with the Mealybug Complex in Cassava Growing Districts of Tamil Nadu, India

An extensive survey was carried to study the diversity of predators associated with the mealybug complex in the cassava growing districts viz., Salem, Namakkal, Erode, Tiruppur and Coimbatore of Tamil Nadu, India from January to September, 2021. The survey revealed the dominance of Phenacoccus manihoti Matile-Ferrero 1977 (Hemiptera: Pseudococcidae) than other mealybug species in all the surveyed districts. The incidence of P. manihoti ranged from 12 to 90 per cent while Paracoccus marginatus Williams and Granara de Willink 1992 (Hemiptera: Pseudococcidae) incidence was found to be between 8 and 54 per cent. The incidence of Ferrisia virgata Cockerell 1893 (Hemiptera: Pseudococcidae) was found to be very low (8-16%) compared to other mealybug species. Association of total predators with P. manihoti were found to be maximum (30.87%) followed by the total predators with P. marginatus (6.49%) whereas 0.53 per cent of total predators associated with F. virgata. The fourteen different predators viz., Cryptolaemus montrouzieri Mulsant 1853 (Coleoptera: Coccinellidae), Menocheilus sexmaculatus Fabricius 1781 (Coleoptera: Coccinellidae), Anegleis cardoni Weise 1892 (Coleoptera: Coccinellidae), Hyperaspis maindroni Sicard 1929 (Coleoptera: Coccinellidae), Brumoides suturalis Fabricius 1798 (Coleoptera: Coccinellidae), Scymnus spp. (Coleoptera: Coccinellidae), Chrysoperla spp. (Neuroptera: Chrysopidae), Mallada spp. (Neuroptera: Chrysopidae), Spalgis epeus Westwood 1851 (Lepidoptera: Lycaenidae), Geocoris spp. (Hemiptera: Geocoridae), Cardiastethus spp. (Hemiptera: Anthocoridae), Diadiplosis spp. (Diptera: Cecidomyiidae), Oxyopes spp. (Araneae: Oxyopidae) and Argiope spp. (Araneae: Araneidae) were found to associated with the mealybug species viz.,P. manihoti, P. marginatus and F. virgata. Among the predators of the mealybug complex, the most relative abundant species were H. maindroni (11.74%) associated with P. manihoti and C. montrouzieri (6.49%) associated with P. marginatus followed by S. epeus (0.67%) associated with F. virgata. The diversity of predators assessed through Simpson’s Index of Diversity, Shannon-Wiener, Pielou’s Evenness and Margalef indices revealed highest species diversity, species richness and species evenness in Namakkal district.

COMPARATIVE BIOLOGY AND PREDATORY POTENTIAL OF Cryptolaemus montrouzieri ON MEALYBUGS

Comparative biology of Cryptolaemus montrouzieri on Maconellicoccus hirsutus and Pseudococcus citri revealed that it had completed its life cycle successfully on both species. The mean total developmental period (egg to pupa) was 18.1 days, when reared on P. citri and it was 20.9 days in M. hirsutus. The adults developed on P. citri had high fecundity 284.2 eggs / female and longevity 47.0 days than those developed on M. hirsutus. Analysis on the growth indices of C. montrouzieri showed more preference on P. citri with high suitability index of 2.51 than M. hirsutus (1.78). Among two life stages, adults of C. montrouzieri was more voracious and each adult consumed an average 258.7, 352.1 and 217.3 numbers on M. hirsutus while, it was 323.8, 715.6 and 328.6 number of eggs, nymphs and adults for P. citri, respectively. The grubs required 221.1, 55.1 and 36.6 numbers of M. hirsutus and 1079.0, 341.3 and 41.0 number of eggs, nymphs and adults of P. citri, respectively to complete life stages. Out of different instars of C. montrouzieri, third and fourth instars required around 92.1, 78.5 and 85.9 per cent and 88.9, 93.5 and 79.0 per cent of total eggs, nymphs and adults of P. citri and M. hirsutus consumed, respectively.

EVALUATION OF CHRYSOPERLA CARNEA COMPLEX AND COCCINELLID PREDATORS AS BIOCONTROL AGENTS OF RICANIA SPECULUM (WALKER, 1851) (HEMIPTERA RICANIIDAE)

Ricania speculum is an alien insect feeding on several host plants belonging to several families, including important vegetables, crops, ornamental plants, wild plants as well as trees. For the first time, recently, Chrysoperla sp. and coccinellid beetles have been observed preying on this species in the field on Citrus sp. and Laurus nobilis plants. The main purposes of this work were to evaluate the possible predation capability of these groups of insects and determine their prey preference in laboratory trials. In the choice trials, R. speculum nymphs were paired in a confined space and exposed for 24h to single predators: Ch. carnea complex and to the coccinellids Cryptolaemus montrouzieri, Adalia bipunctata, Coccinella septempunctata, and Propylea quatuordecimpunctata. Specimens of Aphis rumicis, an aphid frequently found on her baceous plants, were used as a control prey. In the cage trials, a single Ch. carnea complex second-instar larva was placed into a jar containing a tomato plant with ten R. speculum nymphs. In the choice trials, a high mortality percentage of both preys was observed with the Ch. carnea complex, while in those with Coccinellids only high A. rumicis mortality was reported. In the cage trials, 13% mortality of R. speculm was recorded after 24h while after 72h and 168h prey mortalities reached 18% and 25%, respectively. The results of the study showed that larvae of the Ch. carnea complex could be potential predators of R. speculum, while coccinellids do not seem promising predators of this alien species.

Intraguild Interactions between the Mealybug Predators Cryptolaemus montrouzieri and Chrysoperla carnea

The ladybird Cryptolaemus montrouzieri and the green lacewing Chrysoperla carnea have shown potential for use in augmentative biological control of mealybug pests in greenhouse crops. In the context of combining these predators within an integrated pest management system, the risk of negative intraguild interactions between both predators was evaluated in a laboratory setting. Different life stages of either predator were confronted in petri dish arenas containing a Ficus benjamina leaf, and after 24 h the incidence and direction of intraguild predation (IGP) was recorded for each combination. The effect of adding Planococcus citri nymphs or Ephestia kuehniella eggs as extraguild prey on the level of IGP was also studied. IGP was frequently observed between the two predator species and was asymmetrical in favour of C. carnea in most cases. The presence of extraguild prey reduced the number of IGP events between the predators to a similar extent. The relevance of the observed intraguild interactions for the combined use of these predators in protected cultivation is discussed.

Potential displacement of the native Tenuisvalvae notata by the invasive Cryptolaemus montrouzieri in South America suggested by differences in climate suitability

Tenuisvalvae notata (Mulsant) (Coccinellidae) is a predatory ladybird beetle native to South America. It specializes in mealybugs prey (Pseudococcidae), but relatively little is known about its ecology. In contrast, the ladybird beetle Cryptolaemus montrouzieri Mulsant (Coccinellidae) is indigenous to Australia and has been introduced to many countries worldwide including Brazil for biological control of mealybugs. The potential impacts of these introductions to native coccinellids have rarely been considered. The software CLIMEX estimated the climate suitability for both species as reflected in the Ecoclimatic Index (EI). Much of South America, Africa, and Australia can be considered climatically suitable for both species, but in most cases, the climate is considerably more favorable for C. montrouzieri than T. notata, especially in South America. The CLIMEX model also suggests seasonal differences in growth conditions (e.g. rainfall and temperature) that could affect the phenology of both species. These models suggest that few locations in South America would be expected to provide T. notata climatic refugia from C. montrouzieri. Although other ecological factors will also be important, such as prey availability, this analysis suggests a strong potential for displacement of a native coccinellid throughout most of its range as a consequence of the invasion by an alien competitor.

Use of Sugar Dispensers to Disrupt Ant Attendance and Improve Biological Control of Mealybugs in Vineyard

Planococcus ficus (Signoret) and Pseudococcus comstocki (Kuwana) (Hemiptera: Pseudococcidae) are economically important pests occurring in vineyards, causing severe economic losses for growers and compromising bunch production. The partial effectiveness of insecticides used in controlling mealybug infestations as well as their high impact on the environment and on human health have led to the research of alternative and sustainable control methods, including biological control. Several natural enemies are reported to be effective against mealybugs, but their activity may be hindered by tending ants. These social insects are known to exhibit a mutualistic relationship with mealybugs, resulting in extremely aggressive behavior against beneficial insects. Consequently, this study explored a method to mitigate ant attendance by means of sugar dispensers in order to improve ecosystem services, as well as decrease mealybug infestation in vineyards. Field trials were carried out in four commercial vineyards of Northern Italy infested by mealybugs, in which Anagyrus vladimiri Triapitsyn (Hymenoptera: Encyrtidae) and Cryptolaemus montrouzieri Mulsant (Coleoptera: Coccinellidae) were released as biological control agents. Our results showed that sugar dispensers reduced ant activity and mealybug infestation, leading to a significant enhancement of ecosystem services. The technique showed a great potential in boosting biological control against mealybugs in field conditions, though the field application seemed to be labour intensive and needs to be replicated for a multi-year evaluation.

Genomic insight into diet adaptation in the biological control agent Cryptolaemus montrouzieri

Background The ladybird beetle Cryptolaemus montrouzieri Mulsant, 1853 (Coleoptera, Coccinellidae) is used worldwide as a biological control agent. It is a predator of various mealybug pests, but it also feeds on alternative prey and can be reared on artificial diets. Relatively little is known about the underlying genetic adaptations of its feeding habits. Results We report the first high-quality genome sequence for C. montrouzieri. We found that the gene families encoding chemosensors and digestive and detoxifying enzymes among others were significantly expanded or contracted in C. montrouzieri in comparison to published genomes of other beetles. Comparisons of diet-specific larval development, survival and transcriptome profiling demonstrated that differentially expressed genes on unnatural diets as compared to natural prey were enriched in pathways of nutrient metabolism, indicating that the lower performance on the tested diets was caused by nutritional deficiencies. Remarkably, the C. montrouzieri genome also showed a significant expansion in an immune effector gene family. Some of the immune effector genes were dramatically downregulated when larvae were fed unnatural diets. Conclusion We suggest that the evolution of genes related to chemosensing, digestion, and detoxification but also immunity might be associated with diet adaptation of an insect predator. These findings help explain why this predatory ladybird has become a successful biological control agent and will enable the optimization of its mass rearing and use in biological control programs.